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the Creative Commons Attribution 4.0 License.
| 22 Sep 2021
The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China
Abstract. Glaciers continuously affected by climate change are of great concern; their supply and runoff variation tendency under the pressure of increasing populations, especially in dryland areas, should be studied. Due to the difficulty of observing glacier runoff, little attention has been given to establishing high-resolution and long-term series datasets established for glacial runoff. Using the latest dataset using digital elevation models (DEMs) to obtain regional individual glacier mass balance, simulating the spatiotemporal regime of glacier runoff in oases that support almost the entire income in the dryland areas of China (DAC) could be possible. The simulations quantitatively assess glacier runoff, including meltwater runoff and delayed runoff, in each basin of the DAC at a spatial resolution of 100 m from 1961 to 2015, classify glaciers according to the potential climatic risks based on the prediction results. The total glacier runoff in the DAC is (98.52 ± 67.37) × 108 m3, in which the meltwater runoff is (63.43 ± 42.17) × 108 m3, accounting for 64.38 %. Most basins had continuously increasing tendencies of different magnitudes from 1961 to 2015, except for the Shiyang River basin, which reached its peak in approximately 2000. Glacier runoff nurtured nearly 143,939.24 km2 of oasis agricultural areas (OAA) until 2015, while 19 regions with a total population of 14 million were built alongside the oases, where glacier runoff occupies an important place in agricultural, industrial and municipal water consumption. Therefore, providing a long time series of glacier runoff for different river basins is of great significance to the sustainable development of the oasis economy in the arid zones.
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RC1: 'Comment on hess-2021-377', Anonymous Referee #1, 25 Oct 2021
Review HESS The spatiotemporal regime of glacier runoff in oases indicates the potential climatic risk in dryland areas of China
This manuscript calculates timeseries of glacier runoff for the dryland areas of China for the period 1961 until 2015 using the APHRODITE gridded precipitation and temperature products. These estimates of glacier runoff are used to indicate the amount of glacier meltwater that comes from the imbalance and balance component of glacier runoff (referred to as meltwater runoff and delayed runoff, respectively, in the manuscript) and to analyze trends. In the discussion section the amount of glacier runoff is compared with some estimates of the agricultural, industrial and municipal water consumption. All of the analyses are done for 22 basins in the northwestern part of China.
Although the title of this study sounds interesting and could potentially be of interest for HESS, I found this first impression not reflected in the content of the rest of the manuscript. First of all, the poor writing and unfinished or wrong sentence structures make it at many places impossible to understand what actually has been done. Regardless of the writing, the methods are described in a very unsystematic way and many details are missing. Furthermore, I had troubles identifying the added value of this study. The study uses several different existing datasets to calculate annual glacier runoff, which is according to the study a novelty compared to the multi-year mean geodetic mass balances. However, it does not become clear which question(s) can be answered with these annual glacier runoff estimates. A clear link to other terms in the water balance of these oases regions is missing, or a discussion how water from the glaciers reaches the agricultural areas. I even doubt the usefulness of calculating trends if changes in glacier extent are not considered. Overall, I cannot recommend publication of this study. Please find below a few more comments.
P2: ‘Under current climatic conditions, warming causes glaciers to melt and sea level to rise, creating a negative feedback between the two’ -- what is the negative feedback here?
P3: ‘Semi-distributed hydrological models semi-quantitively calculated the proportion of meltwater runoff to total runoff without time series’ -- what is meant with ‘without time series’?
P4: ‘Dataset of spatial distribution of degree day factors for glaciers’ -- since this dataset is so central for the calculations in this study, just giving a link to this data is not acceptable
P5: The table shows the area of the oases in each watershed. Apart from expecting here instead the relative area of OAA and glacier cover, the amount of rain in mm does not give a lot of information on the importance of glacier runoff. Why is glacier runoff not calculated as mm/y?
P7-15 Methods:
A whole page is used to describe different studies and data sources of geodetic mass balances, first describing that two datasets will be compared (Brun and Shean), to later read only the ‘Shean estimation’ is used.
The resolution is 100 m. What does this mean? How does the DDF vary in space? Are the PDD or PDDm calculated for each glacier, for each 100 m, for each basin?
How was the maximum rainfall height determined?
From the description in the manuscript it is also unclear how the precipitation gradient was optimized. Was the ablation calculated based on the same period as the Shean mass balance estimation? And what is ‘H’, the mean elevation of the glacier? In the current formula (equation 4), the elevation between Hmax and Hmap are taken twice into account? Or did I understood something wrong? Should it not be (- delta H)? Why were the vertical gradients interpolated if they are already calculated for each individual glacier?
Like in other parts of the paper, also here discussion parts are mixed up with the methods part and it is confusing to read again about the precipitation gradients in section 2.3.2.
Regarding the uncertainty analyses, what is meant with ‘the PG of each single glacier around the DAC was obtained with geographical simulation’? In a few paragraphs before I read that PG was obtained by fitting the accumulation to the geodetic mass balance and estimated ablation? And why is only the uncertainty in the Shean mass balance estimation considered? What is the uncertainty in the DDF? These can have a large effect also on the accumulation estimates.
For the calculation of glacier runoff and consequently the trend analyses, I do not understand what is meant with the 100 m resolution of this study and how changing glacier area is considered. Are precipitation and temperature calculated for fixed grid cells containing the glacier? Which of the parameters are changing over time to calculate a trend in the glacier runoff? Changes in P and T can affect the total glacier runoff and the partitioning between balanced and imbalanced contributions, but also the changes in glacier extent play a role for the amount of glacier runoff.
P15: ‘The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components (glacier runoff) coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin. What is meant here?
Why is 3.2 a results section? It rather discusses the results? the 3.2 on P18, there is also a 3.2 on P23.
What is the point that the study tries to make in Section 4.1 and 4.2? From the methods section the calculation of the precipitation gradient was already unclear, but the discussion section does not clarify any of these concerns. Hmap and Href are the same? Could the ‘believing’ in one or two maximum rainfall heights not be demonstrated here?
Section 4.3 does in my point of view not add anything to the study.
Regarding section 4.4, it is described that oases in the DAC rely most on glacier runoff and that it maintains soil moisture, vegetation growth and groundwater replenishment. However, without comparing glacier runoff to other sources of water and without describing the pathways of glacier runoff (how does glacier melt become soil moisture?), such conclusions cannot be drawn.
P33: ‘For example, due to increased temperature and reduced glacier runoff, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds’ -- I think such a statement requires a reference. Moreover, a lack of precipitation and snowmelt and increased evaporation caused a severe drought, rather than the small ‘reduced glacier runoff’ contribution.
P33: ‘In the future, glacier runoff will reach its peak when glacier tourism disappears’ -- What is the connection between these two processes?
P34: The linear regression is only introduced in the conclusion (I could not find it elsewhere in the manuscript). Apart from that, how does the study deal with the non-linear change in glacier runoff (peakwater)?
P34: Nothing that is mentioned at point three in the conclusion I can find in the results section. Where do these conclusions come from?
Citation: https://doi.org/10.5194/hess-2021-377-RC1 -
AC1: 'Reply on RC1', Xuejing LENG, 03 Nov 2021
Thank you very much for providing the insightful comments for our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). First of all, we realize that there were many unclear expressions and wrong marks of parameters in the manuscript which confused you. Following your comments, we have modified the corresponding sentence in responding to each specific comment. We will ask a well-established expert to polish our paper in the revised manuscript. According to your all comments, we think the main corrections in the paper are as follows:
- Correct the wrong variable expression in Method (such as ), and put discussion about precipitation dataset and mass balance dataset into supplementary materials and present it in figures or charts.
- For the socio-economic results of glacier runoff, a specific analysis of the impacts of glacier runoff on oases (e.g. using hydrological models) can be supplemented to increase the persuasiveness of this paper.
As for the method part, we think that adjusting the overall narrative structure is useful to express our method more systematically and explain each variable clearly. The revised method part will be 1. Reconciling High-altitude 2. Glacier Runoff and 3. Uncertainty analysis. There are indeed some confusing parts in the method part, such as the comparison of mass balance datasets (lines 124-144). We may change this section into a figure in the supplementary materials attached to the manuscript. However, as precipitation is the most basic link in the water cycle and the most basic element in the whole calculation process, we believe that the reasons for selecting precipitation data need to be further explained and verified. Therefore, we only embellished the language in this part but did not delete the two paragraphs (lines 195-224). The confusing concluding paragraph (lines 251-254) should be deleted, and the methods section should now be clear and not short of details. Thank you again for your guidance.
As pointed in the introduction part (lines 61-68), energy balance models which commonly used in calculating glacier runoff are with low resolution and other physical models perform weak on regional scales. Most studies focus on single glacierized catchments or glacier, or develop corresponding glacier runoff modules in areas where terrestrial observations are abundant. In this paper, a high-resolution calculation method of glacier runoff is developed on a regional scale and be applied in oasis regions in drylands of China to answer the hydrological consequences of glacier runoff, for example, the proportion of water withdrawn in oases due to glacier runoff including delayed runoff and meltwater runoff, in these vital basins in arid areas. Because of our unreasonable words’ allocation in the introduction and application, you may not understand the meaning of this research. Highlight the gap that poor research about high-resolution glacier runoff calculating on regional scales may improve readers’ recognition of this research.
For the doubt “missing a discussion how water from the glaciers reaches the agricultural areas”, we obtained the catchment regions as shapefiles from the RESDC (Resource and Environment Science and Data Center of the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences) on public (lines 89-91). Basins with oases in our article are all originated from glaciers so glacier runoff is bound to affect those oases. While our article focuses on high-resolution glacier runoff calculating on regional scales but not the hydrological distribution model, the accurate value arrived at the oases (how water reached) is not our goal in this paper. We think that the changing proportion of water withdrawals due to glacier runoff under clime change is sufficient to illustrate the threat of glacier runoff to oases. However, following your comment, we think adding a case in one glacier basin to explain the socio-economic consequence caused by glacier runoff will make this paper more persuasive.
The suspicion “the usefulness of calculating trends if changes in glacier extent are not considered” appeared is because the scarce introduction of the glacier extent datasets (lines 87-88, Information about glacier outlines, elevations, and areas was derived from the Randolph Glacier Inventory (version 6.0, https://www.glims.org/RGI/rgi60_dl.html)). Randolph Glacier Inventory, a multisource glacier inventory (lines 145-148), was obtained by overlaying outlines on modern satellite imagery and aggregating the World Glacier Inventory. All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time. Two methods are to use widely to identify changes in glacier extent. One is used the MOD10A1 Snow Cover Daily Global 500m product based on a snow mapping algorithm employing the NDSI (Normalized Difference Snow Index) to obtain the changing of glacier extents (Hall et al., 2016; Muhammad and Thapa, 2021). However, we think that glacier extents changes over the past 55 years cannot be accurately expressed by a 500m product. The other is using satellite imageries in a resolution of 30 m and also the NDSI (Wang et al., 2020; Tak and Keshari, 2020). But the extent is not be as of accurate as the glacier inventory like RGI because of the difficulties to select the least-cloudy scenes. So, we chose the multisource glacier inventory RGI for our research. In addition, we verified our glacier runoff in section 3.2 Glacier Runoff validation testifying our trends over Aksu River Basin (1961-1986, lines 402-405) and Ebinur Lake Drainage Systems (the 1980s, lines 406-407) to be usable even if before 1990. Based on the former uncertainties about obtaining changing glacier extents, we think RGI is the most appropriate while the calculation results are proved to be consistent even in the time before the inventory was constructed (1961-1990), so trends can also be used to indicate changes in local glacier runoff.
Overall, thank you for your doubts and suggestions on our language, method structure, and some narrative details, which make great progress on our research. We still insist that the research is valuable. As oases’ special impacts supporting agriculture, industry, and municipality in arid areas, how much relative stable water is provided by glaciers is a vital problem to be solved. This paper can fill in the gap of glacier runoff calculation on regional scales lack of local terrestrial observations. However, a case of how much glacier runoff arrived oases is needed to add to the discussion section.
Through the above explanation, I hope you can understand the purpose and hope to dispel your doubts.
A detailed point-by-point response to each comment is shown followed and we think the article will be more persuasive after our discussion.
[Reviewer #1 Specific Comment 1] P2: ‘Under current climatic conditions, warming causes glaciers to melt and sea level to rise, creating negative feedback between the two’ -- what is the negative feedback here?
[Response] Following this comment, we apologize for our unclear expression. What we want to point is that warming expedites glaciers to melt and then speeds up raising sea levels under current climatic conditions. The increase in meltwater can alleviate drought in the river basins originated from glaciers like the drylands of China, but sea level rise poses risks to coastal areas, meaning that the meltwater of glaciers is not only a result of climate change but also contributing to the consequences of climate change such as rising sea levels. So, we think we could change the sentence as follows:
“Under current climatic conditions, warming expedites glaciers to melt and meltwater speeds rising sea levels, which is why glaciers are both the result of and contributor to climate change.”
[Reviewer #1 Specific Comment 2] P3: ‘Semi-distributed hydrological models semi-quantitively calculated the proportion of meltwater runoff to total runoff without time series’ -- what is meant with ‘without time series’?
[Response] The semi-distributed hydrological models used in the previous study only semi-quantitatively calculated the proportion of meltwater runoff to the total runoff. For example, Wang et al. (2019) calculated that glacier runoff accounted for 24.4% of the total runoff in combination with the hydrological data of the outlet in the Ebinur Lake Drainage System. Gao et al. (2008) calculated that glacier runoff in the Kai-Kong River Basin accounted for 21.1% in the 1980s and 22.1% in 2000 or the total runoff, respectively. What these researches showed are ratios over time and but not illustrating complete glacier runoff time series, so we say they are ‘without time series’. Perhaps the expression in the original text is not clear enough, we think adding some examples at the end of this sentence for further modification to explain can solve the problem. The corrected sentence is as follows:
“Semi-distributed hydrological models semi-quantitively calculated the mean proportion of glacier runoff to total runoff rather than a time series, such as 21.1% in the Kai-Kong River Basin in the 1980s (Gao et al., 2008) and 24.4% in the Ebinur Drainage System (Wang et al., 2019).”
[Reviewer #1 Specific Comment 3] P4: ‘Dataset of spatial distribution of degree day factors for glaciers’ -- since this dataset is so central for the calculations in this study, just giving a link to this data is not acceptable
[Response] Following this comment, we think that the explanation of this dataset is not obvious enough that we just describe how the dataset is established in our manuscript (Lines 153-155, ‘This paper used the spatial distribution of snowmelt data with a resolution of 0.5° based on a formula built by investigations and observations of 40 different glaciers in the HMA, and the dataset verified the accuracy (Zhang et al., 2006).’). We will correct the unclear sentence and add validation about this dataset in the corrected manuscript as follows:
“This paper used the spatial distribution of degree-day factors (DDFs) for glaciers with a resolution of 0.5° based on a formula built by investigations and observations of 40 different glaciers in the HMA. Map of isolines for the DDFs shows the factors increase gradually from northwest to southeast in western China which is consistent with the varied climatic environment from cold-dry to warm-wet (Zhang et al., 2006).”
[Reviewer #1 Specific Comment 4] P5: The table shows the area of the oases in each watershed. Apart from expecting here instead the relative area of OAA and glacier cover, the amount of rain in mm does not give a lot of information on the importance of glacier runoff. Why is glacier runoff not calculated as mm/y?
[Response] The average annual precipitation (mm/y) for each basin of dryland areas of China is listed in Table 1 to show the spatial precipitation heterogeneity between basins. The intention is to illustrate the scarcity and instability of precipitation in the arid zone and to highlight the importance of glacier runoff providing a relatively stable water amount. The table only provides the average annual precipitation as mm/y, but following this comment, we think we should add the coefficients of variation of precipitation to indicate different water conditions in the study area. Explaining the heterogeneity then readers could understand the effects of glacial runoff on mitigation of water scarcity in arid areas. We used mm/y as the unit of precipitation under the description of precipitation in previous studies, while m3 is used as the unit of glacier runoff to highlight the amount of glacier runoff and facilitate numerical comparison with the amount of agricultural, industrial, and municipal water consumption. According to AQUASTAT (FAO's Global Information System on Water and Agriculture, https://www.fao.org/aquastat/en/), the unit of water withdrawal by sector in different countries is m3. However, we apologize for the lack of pointing out the water withdrawal source. We will add the part as follows:
“The data used in our manuscript is from AQUASTAT (https://www.fao.org/aquastat/en/), The agricultural water consumption at the watershed scale was obtained by averaging the agricultural water consumption statistical data to the land use types of agricultural land and then ranged regional statistics, which was the same with industrial and municipal water consumption.”
[Reviewer #1 Specific Comment 5] P7-15 Methods: Methods:
A whole page is used to describe different studies and data sources of geodetic mass balances, first describing those two datasets will be compared (Brun and Shean), to later read only the ‘Shean estimation’ is used.
[Response] In section 2.3.1 Reconciling High-altitude Precipitation, we first compare the calculation results of mass balance by Brun et al. and Shean et al. using ASTER DEMs and by IceSat-1 (Ice, Cloud, and land Elevation Satellite) in High-mountain Asia. The comparisons are shown in Lines 126 to 131. Since the IceSat-1 datasets were used to calculate the elevation changes of glaciers larger than 5 km2 not reflecting smaller glaciers and ended proving data in 2009, we choose not to use this dataset in our research (Lines 131-134). Excluding IceSat-1 dataset, this paper focused on comparing the Shean Estimation and Brun Estimation to handle a more appropriate dataset. We compare these two datasets in each region of glaciers in dryland areas of China, and point out the main estimates between the two datasets were relatively consistent, but there was a big difference between the uncertainties (Lines 137-145). This is because the Brun Estimation was a mass balance raster dataset with a spatial resolution of 30 m while Shean Estimation calculated the mass balance of each glacier in the RGI (Randolph Glacier Inventory) and for the above reasons, we select Shean Estimation (Lines 145-148). Since the glacier mass balance dataset is a key dataset for this paper's input data, we thought it should take a whole page to explain why we chose this dataset (Shean Estimation) over others (IceSat-1 or Brun Estimation). We apologize for the confusion in this paragraph and for not giving the reader a clear understanding of why we chose Shean Estimation. To explain more clearly why we choose Shean Estimate, we can change this part into a graphic description in the supplementary materials attached to the manuscript, and simplify the description of the mass balance dataset comparisons.
[Reviewer #1 Specific Comment 6] P7-15 Methods: Methods:
The resolution is 100 m. What does this mean? How does the DDF vary in space? Are the PDD or PDDm calculated for each glacier, for each 100 m, for each basin?
[Response] We apologize for the unclear sentence “Considering that the spatial resolution of this paper was 100 m, monthly positive-degree days ( ) were chosen instead of absolute (Braithwaite & Olesen, 1993), and they were the summed positive daily average temperatures.” (Lines 155-157). Map of isolines for the DDFs shows the factors increase gradually from northwest to southeast in western China which is consistent with the varied climatic environment from cold-dry to warm-wet ((http://www.sciencedb.cn/dataSet/handle/747). The spatial pattern of DDF in High-mountain Asia will be added later (see the response for Specific Comment 3). The PDD is calculated at a spatial resolution consistent with other variables on the 100 m grid scale. The temperature of PDD is calculated according to the APHRODITE data corrected by DEM data, that is, the temperature decreases by 0.65 degrees for every 100 m rise. So, the corrected sentence reads as:
“Monthly positive-degree days ( ) were chosen instead of absolute (Braithwaite & Olesen, 1993) while the calculation method was still summing positive daily average temperatures, on the 100 m grid scale. The temperature was obtained according to the APHRODITE data corrected by DEM data, that is, the temperature decreases by 0.65 degrees for every 100 m rise.”
[Reviewer #1 Specific Comment 7] P7-15 Methods: Methods:
How was the maximum rainfall height determined?
[Response] As the name suggests, the height where rainfall is the largest in the whole section is generally called the maximum rainfall height. A detailed discussion of the maximum rainfall height is presented in section 4.1 Precipitation Correction at High-altitudes (lines 495-543). In the part, we compare the debate between glaciologists and meteorologists about the maximum rainfall height. There has always been controversy over whether there are one or two maximum altitudes in the mountains. Even in the same region, there are different results due to the limitations of the discipline, purpose, method, time, or initial conditions of the study. About this controversy, we have introduced it in detail in the discussion section (lines 495-543).
[Reviewer #1 Specific Comment 8] P7-15 Methods: Methods:
From the description in the manuscript, it is also unclear how the precipitation gradient was optimized. Was the ablation calculated based on the same period as the Shean mass balance estimation?
[Response] The ablation was calculated by the product of and as shown in lines 157-158. The original sentence reads as:
“The monthly spatial distribution of ablation, (m), was calculated by the product of and when the sum of the twelve months was the yearly spatial distribution of ablation, it is (m).”
[Reviewer #1 Specific Comment 9] P7-15 Methods: Methods:
And what is ‘H’, the mean elevation of the glacier?
[Response] The variable ‘H’ is the terrain elevation for each glacier described in line 169 meaning the mean terrain elevation calculated by DEM for each glacier.
[Reviewer #1 Specific Comment 10] P7-15 Methods: Methods:
In the current formula (equation 4), the elevation between and are taken twice into account? Or did I understand something wrong? Should it not be (- delta H)？
[Response] We must apologize for the mistakes in Equation (3) and Equation (4). The correct equations are:
∆H=H-Hrmd (3)
P(cor,d)=P(rmd,d)∙{1+[∆H+(H-Hmap)]} (4)
△H was calculated by the mean terrain elevation from DEM minus DEM aggregated into the same scales as the APHRODITE dataset, Hrmd (m), for each glacier affecting the DAC. And the corrected precipitation, P(cor,d) (m), was calculated as a function of original precipitation data from APHRODIE_MA_v1101_EXR1, P(rmd,d) (m), the vertical precipitation gradient, PG (% m-1), at a daily time step with the maximum rainfall height, Hmap (m) and mean terrain elevation from DEM, H (m), for each glacier.
[Reviewer #1 Specific Comment 11] P7-15 Methods: Methods:
Why were the vertical gradients interpolated if they are already calculated for each individual glacier?
[Response] As the spatial resolution of temperature and precipitation dataset from APHRODITE is 0.25°, which is quite different from the area of glaciers, the vertical precipitation gradient between nearby glaciers may be quite different. Interpolating each glacier’s precipitation gradient could smooth the errors caused by the boundary of the raster data.
[Reviewer #1 Specific Comment 12] P7-15 Methods: Methods:
Like in other parts of the paper, also here discussion parts are mixed up with the methods part and it is confusing to read again about the precipitation gradients in section 2.3.2.
[Response] In section 2.3.1 Reconciling High-altitude Precipitation, we introduce how to calibrate precipitation data through glacier mass balance dataset. We compare the IceSat-1, Brun Estimation, and Shean Estimation to select a more appropriate dataset for our paper (lines 124-148). The degree-day model is used to calculate glacier ablation (lines 150-158). The way to calculate glacier accumulation (corrected precipitation in this paper) is shown in Equation (2) on each glacier is calculated according to the corrected temperature data based on altitude. Then put the result of Equation (2) in Equation (3) and Equation (4), the vertical rainfall gradient could be calculated. And interpolate precipitation gradient to reduce the error caused by grid edge mutation.
[Reviewer #1 Specific Comment 13] P7-15 Methods: Methods:
Regarding the uncertainty analyses, what is meant with ‘the PG of each single glacier around the DAC was obtained with geographical simulation’? In a few paragraphs before I read that PG was obtained by fitting the accumulation to the geodetic mass balance and estimated ablation?
[Response] As mentioned before, we use interpolation to reduce the uncertainty caused by data mutation at a spatial resolution of 0.25 degrees. So, the geographical simulation here refers to the interpolation method. We apologize for our unclear statement. The sentence needs to be corrected as follows:
“The PG of every glacier around the DAC was obtained by combining the accumulation of mass balance and ablation calculated by degree-day factor model, and geographical simulation was used to reduce the impact of data mutations.”
[Reviewer #1 Specific Comment 14] P7-15 Methods: Methods:
And why is only the uncertainty in the Shean mass balance estimation considered? What is the uncertainty in the DDF? These can have a large effect also on the accumulation estimates.
[Response] According to the individual glacier uncertainty (including random error and systematic error) calculated in the Shean Estimation, we calculated the uncertainty of mass balance. We agree that the uncertainty in the DDF can also bring a large effect on the results. However, previous studies used degree-day factors as a constant value, which means, degree-day factor for glaciers was (2±2) (mm ◦C−1 d−1). The DDF we used in this paper is from the map of degree-day factors for glaciers in High-mountain Asia which was built by investigations and observations of 40 different glaciers. This distribution of DDF has improved the accuracy when DDF is just a constant value (2±2) (mm ◦C−1 d−1), so the uncertainty of DDF is not considered as a calculation in this paper.
[Reviewer #1 Specific Comment 15] P7-15 Methods: Methods:
For the calculation of glacier runoff and consequently the trend analyses, I do not understand what is meant with the 100 m resolution of this study and how changing glacier area is considered. Are precipitation and temperature calculated for fixed grid cells containing the glacier?
[Response] The spatial resolution with 100 m was chosen because of the spatial resolution of DEM (version4.1, http://srtm.csi.cgiar.org). We uniformly resampled the precipitation, temperature, and DDF to the spatial resolution of 100 m using the nearest neighbor method before all the calculations in this paper.
[Reviewer #1 Specific Comment 16] P7-15 Methods: Methods:
Which of the parameters are changing over time to calculate a trend in the glacier runoff? Changes in P and T can affect the total glacier runoff and the partitioning between balanced and imbalanced contributions, but also the changes in glacier extent play a role for the amount of glacier runoff.
[Response] The variables needed to calculate glacier runoff include altitude, precipitation, degree-day factor, and temperature, and of which precipitation and temperature are two major variables over time. The altitude is from DEM and the DDF is from the map of degree-factor in HMA which was built by 40 observations rather than a constant value. Randolph Glacier Inventory, a multisource glacier inventory (lines 145-148), was obtained by overlaying outlines on modern satellite imagery and aggregating the World Glacier Inventory. All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time. Two methods are to use widely to identify changes in glacier extent. One is used the MOD10A1 Snow Cover Daily Global 500m product based on a snow mapping algorithm employing the NDSI (Normalized Difference Snow Index) to obtain the changing of glacier extents (Hall et al., 2016; Muhammad and Thapa, 2021). However, we think that glacier extents changes over the past 55 years cannot be accurately expressed by a 500m product. The other is using satellite imageries in a resolution of 30 m and also the NDSI (Wang et al., 2020; Tak and Keshari, 2020). But the extent is not as accurate as of the glacier inventory like RGI because of the difficulties to select the least-cloudy scenes. So, we chose the multisource glacier inventory RGI for our research. In addition, we verified our glacier runoff in section 3.2 Glacier Runoff validation testifying our trends over Aksu River Basin (1961-1986, lines 402-405) and Ebinur Lake Drainage Systems (the 1980s, lines 406-407) to be usable even if before 1990. Based on the former uncertainties about obtaining changing glacier extents, we think RGI is the most appropriate while the calculation results are proved to be consistent even in the time before the inventory was constructed (1961-1990), so trends can also be used to indicate changes in local glacier runoff.
[Reviewer #1 Specific Comment 17] P15: ‘The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components (glacier runoff) coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin. What is meant here?
[Response] The composition of glacier runoff in the Kriya Rivers basin is special compared with other river basins where 93.67% of glacier runoff comes from delayed runoff. Delayed runoff is the part runoff stored in glacial areas during cold seasons and then is released in the warm season. It could be said that delayed runoff is basically determined by rainfall and temperature, which is distinguished from meltwater runoff. Therefore, when extreme precipitation climate occurs, it is easy to cause geologic hazards such as flash floods which should be paid more attention to (Kaltenborn et al., 2010; Shen et al., 2007).
[Reviewer #1 Specific Comment 18] Why is 3.2 a results section? It rather discusses the results? the 3.2 on P18, there is also a 3.2 on P23.
[Response] We apologize for the wrong subheadings in Section 3 Results. The correct subheadings are 3.1 Glacier Runoff during 1961-2015 on P15, 3.2 Glacier Runoff validation on P18, 3.3 Glacier Classification Based on Potential Climatic Risks on P23, and 3.4 The Spatiotemporal Change in Glacier Runoff on P24. We first show the calculated glacier runoff values in the Results, and then verify the calculated glacier runoff. As the data are reliable, we explain the climate risk and the temporal and spatial characteristics of glacier runoff including delayed runoff and meltwater runoff. The discussion section includes some detailed discussions of calculating methods and supplements of the socio-economic impact of glacial runoff on oases.
[Reviewer #1 Specific Comment 19] What is the point that the study tries to make in Section 4.1 and 4.2? From the methods section the calculation of the precipitation gradient was already unclear, but the discussion section does not clarify any of these concerns. Hmap and Href are the same? Could the ‘believing’ in one or two maximum rainfall heights not be demonstrated here?
[Response] Our intention in section 4.1 is to discuss the concept of maximum rainfall height and the different maximum rainfall heights for each region, as well as the debate among meteorologists (lines 507-513) and glaciologists (lines 496-503) about maximum rainfall height. And because of different data or observing methods used, the maximum rainfall height would be different even in the same district (lines 515-529). After these descriptions, Table 2 shows the maximum rainfall height for each region used in this paper. In 4.2 of the discussion section, we want to illustrate the calculated distribution of precipitation gradient (PG) in seven glacier regions (Eastern Tien Shan, Western Tien Shan, Eastern Kunlun, Western Kunlun, Pamir, Qilian Shan, and Karakoram) and the statistical results of PG at different elevation ranges (△H+(H-Hmap), where △H=H-Hrmd). We apologize for the misrepresentation of Equation (3) and Equation (4) again. As a result of this error, the abscissa heading on the left-hand chart in Figure 8 is also incorrect. There is no Href variable in the paper, only maximum rainfall height, Hmap.
As for the debate about whether there are one or two rainfall heights, this paper cannot demonstrate. Equation (3) and Equation (4) in this paper are based on the hypothesis that there is only one maximum rainfall height in a mountain. Corrected high-altitude precipitation decreases with a certain precipitation gradient (PG) corresponding to the height above the only maximum rainfall height. While we have chosen "one rainfall height" as the calculation basis, we think the basis cannot be verified by the conclusions generated on this basis.
[Reviewer #1 Specific Comment 20] Section 4.3 does in my point of view not add anything to the study.
[Response] Our intention in section 4.3 is to explain the rationality of selecting precipitation and temperature as input variables for the calculation of glacier runoff as mentioned in lines 570-572. While glaciers in High-mountain Asia are all continental glaciers, precipitation and temperature are the two major factors of glacier runoff change. Frontal ablation is not considered because glaciers regions in this paper are all continental glaciers. Section 4.3 also shows that, compared with precipitation, the temperature is a more dominant influencing factor in the glacier regions studied in this paper (Azam & Srivastava, 2020; Ban et al., 2020; Huai, 2020; Noël et al., 2020).
[Reviewer #1 Specific Comment 21] Regarding section 4.4, it is described that oases in the DAC rely most on glacier runoff and that it maintains soil moisture, vegetation growth and groundwater replenishment. However, without comparing glacier runoff to other sources of water and without describing the pathways of glacier runoff (how does glacier melt become soil moisture?), such conclusions cannot be drawn.
[Response] The text in the article is that “OAA in the DAC relied most on glacier delayed runoff and meltwater runoff to irrigate and maintain agriculture as well as to maintain soil moisture, vegetation growth, and groundwater replenishment to maintain food security” in lines 579-581. The conclusion that oases are most dependent on glacier runoff was concluded from previous research (Bury et al., 2013; Clouse et al., 2016; Rasul & Molden, 2019). In this part, we compare meltwater runoff and delayed runoff, two components of glacier runoff, with the domestic, industrial, and irrigation consumption water in oases of DAC, in order to show the relative importance of glacier runoff. So hydrological processes are not taken into account in the original text. However, following your comments, we also think that adding a one-year description of the whole hydrological process of glacier runoff to the oases would make our study more convincing. We hope that we can have the opportunity to add an example to illustrate it later.
[Reviewer #1 Specific Comment 22] P33: ‘For example, due to increased temperature and reduced glacier runoff, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds’ -- I think such a statement requires a reference. Moreover, a lack of precipitation and snowmelt and increased evaporation caused a severe drought, rather than the small ‘reduced glacier runoff’ contribution.
[Response] We apologize for missing reference to this sentence “For example, due to increased temperature and reduced glacier runoff, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds”. Based on your comment and the references, we will revise the sentence as follows:
“For example, due to increased temperature and reduced snowmelt or precipitation, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds due to declining runoff, including glacier runoff (Gonzalez et al., 2018; Rasul & Molden, 2019).”
[Reviewer #1 Specific Comment 23] P33: ‘In the future, glacier runoff will reach its peak when glacier tourism disappears’ -- What is the connection between these two processes?
[Response] We apologize for the unclear statement. The sentence should be corrected as follows:
“Under climate change, the reliability of the natural snow on the traditional glaciers has decreased and the ski season has shortened, posing a certain risk to the ski tourism industry (Falk, 2016; Rasul & Molden, 2019). For example, the ski season in Ontario and Quebec was shortened between 2000 and 2010, and the recent record warm winter resulted in a 10-15% drop in visitors (Scott et al., 2012a). At the same time, considering the human influence could accelerate the melting of the glaciers, some glacier tourism has been canceled, such as Tien Shan in Xinjiang of China. Appropriate human activities in glacial areas, especially on the surface of glaciers, such as hiking, skiing, etc., will not be the main cause of glacier loss, these activities can be carried out. However, authorities in Xinjiang have stopped glacier tourism in Tien Shan, arguing that the loss of glaciers will be far greater than glacier tourism. In the past decade, glacier tourism revenue in Xinjiang was less than 1 billion yuan, but the loss caused by glacier collapse or melting was incalculable (Liu, 2016). Similarly, at Yulong Snow Mountain, the local government is considering stopping glacier tourism as the glacier is also shrinking at an accelerating rate. So, as glacier runoff increases, glacier tourism in many regions may stop for balance melting purposes.”
[Reviewer #1 Specific Comment 24] P34: The linear regression is only introduced in the conclusion (I could not find it elsewhere in the manuscript). Apart from that, how does the study deal with the non-linear change in glacier runoff (peakwater)?
[Response] The linear regression was introduced in line 441. We used the function FORECAST.LINEAR in Microsoft Excel to predict glacier runoff in the next decade simply as the annual data of glacier runoff obtained are non-stationary series. The results of prediction are compared with the previous 55 years of calculated glacier runoff data to determine whether the glacier is “Increase continuously”, “Decrease continuously” or is “Reach the peak soon”. The changing slope can be calculated using the mean value of each decade. If the slope is larger than 0.005%, it means increasing continuously, while decreasing continuously happens when the slope is smaller than -0.005%. If the slope is in the range of ±0.005%, it is considered to be reaching the peak of glacier runoff soon (except Karakoram). We apologize for missing the description of this part and will add it to the paper.
[Reviewer #1 Specific Comment 25] P34: Nothing that is mentioned at point three in the conclusion I can find in the results section. Where do these conclusions come from?
[Response] The first sentence in the third conclusion “as a continental glacier, the glacier runoff studied in this paper was mainly regulated by hydrothermal regulation, in which temperature was the dominant factor, followed by precipitation” was from lines 575-577 in section 4.3 Impact factors. We apologize for the wrong number in the second sentence “since the water source of the oases in the DAC was mostly glaciers and the total GDP of the OAAs accounted for 76.92% of that of the northwestern DAC, glacier runoff had a greater impact on local agriculture, animal husbandry, and economy” from lines 584-585, the correct proportion is 79.86%. And the third sentence “in the future, it is necessary to quantify the impact of each change in the cryosphere on social production factors more precisely” is a summary statement based on the impact factors of glacier runoff and its socio-economic consequences.
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AC4: 'Supplementary Reply on RC1 (Methods, Glacier Area Change, and Oases)', Xuejing LENG, 22 Nov 2021
Nov 22, 2021
Thanks again for your helpful and valuable comments on our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). After studying your comments carefully, we have made some corrections which we hope to meet with approval.
- First of all, we rewrite the Methods and annotate parameters correctly. As for some details we have discussed too much, such as the reasons for choosing Shean Estimation and APHRODITE, we use charts and figures to illustrate them in supplementary materials. We also add the methods to calculate the glacier area change. The revised Methods with supplementary materials are attached in the supplementary materials.
- We add the analysis of changes in glacier areas. Glacier outlines were extracted from Landsat TM scenes in the two periods (Region1985-1995 and Region1995-2005) in each basin at the end of ablation seasons (September to November), respectively, in Google Earth EngineTM (hereafter, GEE) based on band ratio segmentation method (Guo et al., 2015; Paul et al., 2009; Racoviteau et al., 2009). We also add an analysis of changes in glacier area in Results.
- We think your suggestion "missing a discussion how water from the glaciers reaches the agricultural areas " should be further discussed. While our article focuses on high-resolution glacier runoff calculating on regional scales but not the hydrological distribution model, the accurate value arrived at the oases (how water reached) is not our goal in this paper. As rivers in DAC are nourished to a high degree by glacier meltwater and also the glacier meltwater is the main artery for the oases in the DAC (Kaser et al., 2010, Wang et al., 2013). Changes in glacier runoff could alter the runoff in the whole river basin. However, the contribution of glacier runoff to oases is fuzzy and hard to quantify (Tino et al., 2013). Most studies also show that glacier runoff is crucial to oases, but there is no quantitative study on how it affects oases (Chen et al., 2019; Fang et al., 2018; Ma et al., 2015; Patrick et al., 2015; Su, 2002; Wang et al., 2012; Yang et al., 2015; Zhang et al., 2021). So, we think that the changing proportion of water withdrawals due to glacier runoff under clime change is sufficient to illustrate the threat of glacier runoff to oases.
Hope the revised sections meet your requirements.
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AC1: 'Reply on RC1', Xuejing LENG, 03 Nov 2021
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RC2: 'Comment on hess-2021-377', Anonymous Referee #2, 04 Nov 2021
Review of “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” by Leng et al. (2021)
The manuscript of Leng et al. derives timeseries of glacier runoff for the dryland areas of China for the period 1961 until 2015 using previously published geodetic mass balance estimates and APHRODITE gridded precipitation and temperature products. Their estimates of glacier runoff are used to indicate the amount of glacier meltwater that comes from the imbalance and balance component of glacier runoff (referred to as meltwater runoff and delayed runoff, respectively, in the manuscript) and to analyze trends. Their analyses are done for 22 basins in northwestern China.
While I find the topic of this paper both an interesting and valuable one for HESS and the dryland areas of China in general, this study is disjointed and left me confused as to the methods and validity of the results. The paper is not well organized, with some topics discussed in far too much detail, often without clearly informing the reader as to a particular method or result. Other topics are either not fully explained, or introduced in different parts of the manuscript, with sometimes conflicting descriptions. The writing and language of this paper requires major improvement if it is to be considered for publication, a careful reading is not sufficient to understand the methods and results – the reader is left to guess how many particular methods were conducted. The sloppy nature of this paper causes confusion with frequent occurrences fragmented explanations and changing or vague terminology and units. Like the Reviewer 1, I cannot recommend this manuscript for publication. However, because I see potential value in the work and great value in this topic, I have included more detailed comments below.
Major comments:
1. Many methods are not well explained: I don’t understand how you get precipitation. You use the 0.25° spatial resolution daily precipitation datasets from the Asian Precipitation – Highly Resolved Observational Data Integration Towards Evaluation Of Water Resources (APHRODITE). But then you state that you “Used the Shean estimation to optimize the precipitation gradient per glacier”. Shean provides annual mass balance – not precipitation, and does not use any precipitation data, so how specifically are you using his method or data? Equations 2, 3 and 4 only use elevation data and APHRODITE precip and temperature data.. not glacier mass balance data.
a. In the next line you state that you are using a precipitation gradient to correct the original APHRODITE data. You then use this gradient “PG” in equations but then never state how you get the gradients until L253-254: “PG in this paper was obtained by interpolation using the mass balance algorithm and geostatistics method”. This is an important point and should be introduced together and fully described, currently this line doesn’t tell us how you get the PG. (Also, is PG a widely used abbreviation for precipitation gradient? I haven’t seen this used).
b. L214, “The precipitation was corrected by the Shean estimation for high-altitude precipitation gradients…”, again, what is this correction, I can’t find any precipitation gradient work in Shean et al. (2020). You have annual mass balance from Shean et al. (2020), precipitation data from APHRODITE, and then estimate ablation with a PDD model. How you use these three datasets in conjunction is not clear.2. L153-156 The PDD values must be stated, what is the range of values? Perhaps show a map of them as a supplemental figure. Further, the uncertainty around these values should be quantified.
3. The terms monthly delayed runoff and meltwater runoff are poorly defined. Is monthly delayed runoff a mix of seasonal snow melt runoff and rainfall over the glacier? In lines 184-186 is Ta meant to be T1? In lines 290-292 you better clarify the terms, which should not be occurring in the results, and still leave the reader confused: “Glacier runoff included delayed runoff that was stored rainfall in the cold seasons and released rainfall in the ablation seasons, while meltwater runoff was caused by glacier mass balance, which was also called excessive meltwater runoff or the imbalanced part of glacial runoff”. Do you mean stored snowpack in the cold season? Or both stored seasonal snowpack and stored rainfall in the cold season? Released rainfall in the ablation seasons?
4. Many other terms are undefined, e.g.: L347 What is “glacier runoff recharge”?
5. Some references are inappropriate.
a. E.g. in your submission you do not cite the information stated in L597-598 about California, then in your response to Reviewer 1 you state: “For example, due to increased temperature and reduced snowmelt or precipitation, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds due to declining runoff, including glacier runoff (Gonzalez et al., 2018; Rasul & Molden, 2019).” --- Rasul and Molden (2019) merely reference the Gonzalez work, and do not offer any data on this so is not suitable to be referenced here. The Gonzalez work can be found here: https://nca2018.globalchange.gov/downloads/NCA4_Ch25_Southwest_Full.pdf, and does not ever mention glaciers.
b. An additional example is in L341 Barnett et al. (2005) is a review paper and did not “simulate glacial runoff” as you claim.6. Using RGI glacier outlines for 1961-2018 is not appropriate for a 100m resolution study. At least an error analysis on the effect of not incorporating glacier area change should be added.
a. In response to Reviewer 1 you state that the RGI polygons were “All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time.” This is close to the case, but as pointed out by Shean et al. (2020)
b. source image timestamps used for RGI polygon digitization (~1998–2014) and the DEM timestamps. This means that the polygons were digitize ANY time between those dates, and contain information about the date.
c. So using a single polygon of 1998-2014 origin is either not appropriate, or requires an uncertainty analysis (which should be included regardless).
d. Also, as detailed by Guo et al. (2017) the first Chinese Glacier inventory was finished in 2002 and covered CGI-1 was compiled based on topographic maps and aerial photographs acquired during the 1950s–80s – so would be a potentially suitable starting outline for you study, then updating to the CGI-2 dating to 2006-2010, compiled by Guo et al. (2017): https://www.cambridge.org/core/journals/journal-of-glaciology/article/second-chinese-glacier-inventory-data-methods-and-results/386DAB512F4869D3335E2DE24B0F43EBSpecific comments:
Any use of numbers should spell out the number if below 10, e.g. 7 regions --> seven regions.
Please use significant digits e.g. L107-108
L15 Is this total annual glacier runoff? Specify time in the sentence or units.
L29 Add “Glaciers and ice sheets are the….”
L35 This is not a feedback, it is a one-way relationship, glaciers melt, producing runoff, increasing sea level. These citations do not fit your point.
L51-57 The problem is not clearly stated here. You state that “Continuous yearly mass balance data for long time series could not be calculated effectively due to the time consumption and high energy consumption of field observations (Brun et al., 2017; Shean et al., 2020).” This is poorly worded and incorrect. Long time series cannot be calculated because the data don’t exist, which in turn is because field observations are logistically and financially difficult.
L62 Two problems here, one, this is an incomplete sentence, and further, why is the resolution so low? Perhaps because the data are not sufficient to use at finer resolutions? “…while the energy balance model could be applied in 62 large regions but with low resolution (such as 0.25 degrees (Sakai et al., 2015))”.
L99 erased the range?
L102 7 glaciers? Or 7 glacier regions?
Figure 1 Font is too small in axes and legend (commonly in many figures)L122-123 Doesn’t make sense. You are implying that you did the work of Shean et al. (2020).
L126-148 Way too long of a description of these studies, if you want to show the comparison in lines 136-145, use a table, this is hard to read.
L267 Blocks represent modules (add the s)
L289-290 “and we overcame the difficulty of large-scale geodetic mass balance assessment” What? Brun et al. (2017) and Shean et al. (2020) did this.
L300-301 “The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin”, wouldn’t the opposite be true? Delayed runoff is not directly from glacier wastage (stored seasonal precip), so is more sustainable than ice wastage.
Figure 3 Units on runoff?? The legend just says “5.6”. How useful are raw runoff numbers versus percent contributions of total river discharge?
L323-338 Replace most this paragraph with a table and reference that table with a few lines.
L324 Glaciers should be lowercase.
Citation: https://doi.org/10.5194/hess-2021-377-RC2 -
AC2: 'Reply on RC2', Xuejing LENG, 14 Nov 2021
Nov 14, 2021
Thank you very much for your helpful and valuable comments on our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). After studying your comments carefully, we have made some corrections which we hope to meet with approval. First of all, we realize that there were many unclear expressions and wrong marks of parameters in the manuscript which confused you. Following your comments, we have modified the corresponding sentence in responding to each specific comment. We will ask a well-established expert to polish our paper in the revised manuscript. According to your all comments, we think the main corrections in the paper are as follows:
1. Rewrite the Methods. We annotate parameters correctly, explain the meanings of parameters clearly, and supplement the calculations of ablation and positive-degree days. As for some details we have discussed too much, such as the reasons for choosing Shean Estimation and APHRODITE, we use charts and figures to illustrate them in supplementary materials.
2. Check references to make sure they are referred to correctly. Adjust texts, legends, and parameters in each figure make them accurate and easy to read.
3. Add the uncertainty analysis of glacier area change. We decided to use Landsat TM/ETIM+ scenes on GEE to obtain the changes of glacier area during each period of dryland areas of China from 1985 to 1995 and 1995 to 2005. Following your comment, glacier areas during 2005-2015 were represented by the second Chinese Glacier Inventory (CGI-2). We compare glacier areas from remote sensing imageries with RGI in each period to analyze uncertainties brought by glacier area change. If some input scenes are masked after the cloud algorithm, we use RGI instead in these regions. The codes for calculating glacier areas are attached at the end of the response.
4. For the socio-economic results of glacier runoff, a specific analysis of the impacts of glacier runoff on oases (e.g. using hydrological models) can be supplemented to increase the persuasiveness of this paper.
A detailed point-by-point response to your comment and suggestion is as follows:
[Reviewer #2 Major Comment 1] Many methods are not well explained: I don’t understand how you get precipitation. You use the 0.25° spatial resolution daily precipitation datasets from the Asian Precipitation – Highly Resolved Observational Data Integration Towards Evaluation Of Water Resources (APHRODITE). But then you state that you “Used the Shean estimation to optimize the precipitation gradient per glacier”. Shean provides annual mass balance – not precipitation, and does not use any precipitation data, so how specifically are you using his method or data? Equations 2, 3, and 4 only use elevation data and APHRODITE precip and temperature data.. not glacier mass balance data.
[Response] We are sorry for our disordered structure in Methods which confused you so much. Since there were some mistakes in Equations 3 and 4 and omitting an Equation about calculating ablation on a glacier, correct and complete Equations on reconciling high-altitude precipitation are as follows:
“By=Ab,y+Ac,y=∫(Ab+Ac)dt (1)
Ab,y=DDF×PDDy (2)
Ac,d={(Pcor,d,Ta≤0@(1-Ta/T1 ) Pcor,d,0<Ta≤4@0,Ta>4)} (3)
∆H=H-Hrmd (4)
Pcor,d=Prmd,d∙{1+[∆H+(H-Hmap)]∙PG∙0.01} (5)”
Eq.1 shows the mass balance (By) is the sum of accumulation (Ac,y) and ablation (Ab,y) at a yearly time step of each glacier. Eq.2 shows the yearly ablation is the product of the degree-day factor (DDF) and positive-degree days (PDDy) of each glacier obtained in the daily temperature dataset. While precipitation is separated into solid and liquid by temperature, only solid precipitation, snow, count as atmospheric mass accumulation. Eq.3 indicates the calculation about daily accumulation by corrected high-altitude temperature (Ta), which decreases 0.65 degrees per 100 m rise corrected by DEM data. Eq.4 and Eq.5 show the reconciled high-altitude precipitation (Pcor,d) was calculated as a function of original precipitation data from APHRODITE (Prmd,d), the vertical precipitation gradient (PG), the mean terrain elevation from DEM (H), the aggregated elevation at a spatial resolution with 0.25 degrees consistent with APHRODITE (Hrmd), and maximum rainfall height (Hmap) at a daily time step for each glacier.1. We use the Shean Estimation of the mass balance and their uncertainties as annual mass balance (B_y) while Shean Estimation showed the average mass balance from 2000 to 2018 for each glacier.
2. Using the product of the distribution map of DDF and PDDy to obtain the yearly ablation (Ab,y) at a grid scale with a spatial resolution of 100 m. For each glacier, yearly ablation (Ab,y) was calculated on values within the zones of RGI shapefiles.
3. The annual accumulation (Ac,y) on each glacier was calculated based on 1 and 2.
4. The annual accumulation (Ac,y) of each glacier calculated in 3 was substituted into Eq. 3-5, the vertical precipitation gradient (PG) of each glacier was obtained by combining elevation data, corrected high-altitude temperature data (Ta), and the maximum rainfall height (Hmap) of each glacier region.
5. As the spatial resolution of the temperature and precipitation dataset from APHRODITE is 0.25°, which is quite different from the area of glaciers, the vertical precipitation gradient between nearby glaciers may be quite different. We interpolated each glacier’s precipitation gradient to smooth the errors caused by the boundary of the raster data.
In Step 5, the map of interpolated vertical precipitation gradient (PG) was obtained. Using original temperature and precipitation (Prmd,d) from APHRODITE according to Eq.3-5 to calculate corrected high-altitude precipitation (P_(cor,d)) and accumulation (A_(c,d)) at a daily step on a grid cell. The daily ablation (Ab,d) on a grid cell could be calculated by Eq. 2, and then the daily mass balance (Bd) on a grid cell could be obtained according to Eq. 1. The grid cell is unified at a spatial resolution with 100 m in this step.
The above six steps are the complete process of the raster dataset of regional glacier mass balance obtained after high-altitude precipitation correction by Shean Estimation in this paper.
[Reviewer #2 Major Comment 1. a] In the next line you state that you are using a precipitation gradient to correct the original APHRODITE data. You then use this gradient “PG” in equations but then never state how you get the gradients until L253-254: “PG in this paper was obtained by interpolation using the mass balance algorithm and geostatistics method”. This is an important point and should be introduced together and fully described, currently this line doesn’t tell us how you get the PG. (Also, is PG a widely used abbreviation for precipitation gradient? I haven’t seen this used).
[Response] We are sorry again for the unclear narrative structure in Methods. Vertical precipitation gradients (PG) were calculated after obtaining accumulation (Ac) (corrected high-altitude precipitation relevant to high-altitude temperature, Pcor) by subtracting mass balance (By) from Shean Estimation to ablation (A_b) for each glacier. The PG is just an abbreviation for precipitation gradients and a parameter in equations in this paper but not a widely used abbreviation. We got a map of interpolated precipitation gradients (PG) to smooth the errors caused by the boundary of the raster data at a spatial resolution of 0.25 degrees. Then, using original temperature and precipitation (Prmd,d) from APHRODITE to calculate corrected high-altitude precipitation (Pcor,d) and accumulation (Ac,d) at a daily step on a grid cell. Daily ablation (Ab,d) on a grid cell could be calculated by Eq.2 and we obtained map of daily mass balance for glacier regions at a spatial resolution of 100 m.[Reviewer #2 Major Comment 1. b] L214, “The precipitation was corrected by the Shean estimation for high-altitude precipitation gradients…”, again, what is this correction, I can’t find any precipitation gradient work in Shean et al. (2020). You have annual mass balance from Shean et al. (2020), precipitation data from APHRODITE, and then estimate ablation with a PDD model. How you use these three datasets in conjunction is not clear.
[Response] Thanks for your comment and we apologize for the unclear paragraphs in Methods. We will rewrite the method section to avoid confusion and make it clearer. As mentioned in the previous responses, mass balance with uncertainties for each glacier from Shean Estimation provided annual mass balance (By). Positive-degree days (PDD) are accumulated by daily temperature from APHRODITE corrected by DEM (0.65℃/100 m). Ablation (Ab,y) is calculated by the product of PDD and map of DDF provided by Zhang et al. After subtracting mass balance to ablation, annual accumulation (Ac,y) from 2000-2018 (Shean et al., 2020) for each glacier could be obtained. According to Eq.3-5, the precipitation gradient for each glacier could be calculated with the help of original precipitation (Prmd,d) from APHRODITE. Substituting the map of interpolated precipitation gradient and precipitation from APHRODITE into Eq.1-5, yearly maps of mass balance for glaciers in dryland areas of China could be obtained.[Reviewer #2 Major Comment 2] L153-156 The PDD values must be stated, what is the range of values? Perhaps show a map of them as a supplemental figure. Further, the uncertainty around these values should be quantified.
[Response] Thanks for your suggestion and following your comment, we add a description of positive-degree days as follows:
“Monthly positive-degree days (PDDm) were chosen instead of absolute PDD (Braithwaite & Olesen, 1993) which were summed positive daily average temperatures. However, as we used temperature from APHRODITE, uncertainties around temperature and PDDm could not be quantified. We could add a map of PDDm as a supplemental figure.[Reviewer #2 Major Comment 3 a] The terms monthly delayed runoff and meltwater runoff are poorly defined. Is monthly delayed runoff a mix of seasonal snowmelt runoff and rainfall over the glacier?
[Response] We are sorry for missing detailed and accurate definitions of delayed runoff and meltwater runoff. Delayed runoff is defined in lines 178-181 as “Based on the definition of glacier runoff, the runoff includes two parts. One is the precipitation on glaciers stored in the non-melting season and released in the melting season, which is called delayed runoff (Kaser et al., 2010; Pritchard, 2019; Shean et al., 2020)”. Actually, glacier runoff in this paper refers to the runoff generated in glacier regions. According to Eq.1, mass balance (By) is the sum of accumulation (Ac,y) and ablation (Ab,y) at a yearly time step of each glacier. While mass balance is a positive value, it means there is accumulation caused by precipitation on the glacier, and the amount greater than 0 forms runoff according to the PDD of each month. So, delayed runoff refers to the amount of precipitation accumulated at high altitudes after offsetting by the ablation and stored in the mountains as snow in the cold seasons and discharged in the warm seasons, not including meltwater runoff.[Reviewer #2 Major Comment 3 b] In lines 184-186 is Ta meant to be T1?
[Response] We are sorry for these mistakes. In lines 184-186, what T_a meant to say is T_1, which is 4 ℃ in this paper. We will replace T_1 in the original text with 4 ℃ used in the actual calculation to avoid confusion.[Reviewer #2 Major Comment 3 c] In lines 290-292 you better clarify the terms, which should not be occurring in the results, and still leave the reader confused: “Glacier runoff included delayed runoff that was stored rainfall in the cold seasons and released rainfall in the ablation seasons, while meltwater runoff was caused by glacier mass balance, which was also called excessive meltwater runoff or the imbalanced part of glacial runoff”. Do you mean stored snowpack in the cold season? Or both stored seasonal snowpack and stored rainfall in the cold season? Released rainfall in the ablation seasons?
[Response] We apologize for the unclear sentence. We divided glacier runoff into two parts in this paper while one is delayed runoff, the other is meltwater runoff. As mentioned in the former response, delayed runoff refers to the amount of precipitation accumulated at high altitudes after offsetting by the ablation and stored in the mountains as snow in the cold seasons and discharged in the warm seasons, not including meltwater runoff. Meltwater runoff, which is also called excessive meltwater runoff or the imbalanced part of glacier runoff, is caused by glacier mass balance. While mass balance is a negative value, glaciers recede during warm seasons. Delayed runoff emphasizes the release of precipitation offsetting ablation stored in cold seasons on glaciers during warm seasons, while meltwater runoff emphasizes the amount of melting of the glacier itself due to its mass balance during warm seasons. The corrected sentence reads as:
“To be precise, glacier runoff in this study is runoff generated in glacier regions, including meltwater runoff and delayed runoff. Delayed runoff was caused by remaining precipitation stored in cold seasons and discharged in warm seasons after offsetting ablation. Meltwater runoff, which was also called excessive meltwater runoff or the imbalanced part of glacier runoff, was caused by mass loss of glaciers when atmospheric accumulation cannot offset ablation on glaciers.”[Reviewer #2 Major Comment 4] Many other terms are undefined, e.g.: L347 What is “glacier runoff recharge”?
[Response] We apologize for the undefined term “glacier runoff recharge” in lines 347-348 “The percentage of glacier runoff recharge calculated by the DDF model was between 5% and 15% based on the first Chinese inventory and monthly precipitation and temperature data from the National Meteorological Centre (Gao et al., 2010)”. Glacier runoff recharge here refers to glacier runoff as a percentage of surface runoff recorded by hydrological stations. The corrected sentence reads as:
“The percentage of glacier runoff calculated by the DDF model was between 5% and 15% based on the first Chinese inventory and monthly hydrothermal data from the National Meteorological Centre (Gao et al., 2010).”
[Reviewer #2 Major Comment 5 a] Some references are inappropriate. E.g. in your submission you do not cite the information stated in L597-598 about California, then in your response to Reviewer 1 you state: “For example, due to increased temperature and reduced snowmelt or precipitation, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds due to declining runoff, including glacier runoff (Gonzalez et al., 2018; Rasul & Molden, 2019).” --- Rasul and Molden (2019) merely reference the Gonzalez work, and do not offer any data on this so is not suitable to be referenced here. The Gonzalez work can be found here: https://nca2018.globalchange.gov/downloads/NCA4_Ch25_Southwest_Full.pdf, and does not ever mention glaciers.
[Response] In the response to Reviewer #1, we only added references neglecting to check the contents of them. Following your comments, we recognize no matter Gonzalez et al. (2018) or Rasul & Molden (2019) are inappropriate referred here. Thanks again for providing the Gonzalez work and your valuable comments. Here we would like to state the impact of glacier shrinkage on hydropower as follows:
“Some countries where the main source of electricity is hydropower, glacier runoff contributed significantly to its origination such as France (Milner et al., 2017) and Norway (Andreassen et al., 2005). 19 hydropower plants in the glacier-fed Rhone River supplied 25% of French hydropower and 15% of hydropower used runoff comes from glacierized basins in Norway.”[Reviewer #2 Major Comment 5 b] Some references are inappropriate. An additional example is in L341 Barnett et al. (2005) is a review paper and did not “simulate glacial runoff” as you claim.
[Response] We apologize for the misquotation of Barnett et al. (2005) which is a review paper not mentioning glacier runoff simulation. Even the contents in Section “Impacts on regional water supplies” were about Himalaya-Hindu Kush region not dryland areas of China. So we delete this reference here and add a new one. The corrected complete sentence with references reads as:
“Some studies (Hussain et al., 2019; Li et al., 2018; Shen et al., 2004; Wang et al., 2015; Wu et al., 2018; Yang et al., 2015; Ye et al., 2017) simulated glacial runoff in the DAC by qualitative or semi-quantitative methods or by using models.”[Reviewer #2 Major Comment 6] Using RGI glacier outlines for 1961-2018 is not appropriate for a 100m resolution study. At least an error analysis on the effect of not incorporating glacier area change should be added.
a. In response to Reviewer 1 you state that the RGI polygons were “All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time.” This is close to the case, but as pointed out by Shean et al. (2020)
b. source image timestamps used for RGI polygon digitization (~1998–2014) and the DEM timestamps. This means that the polygons were digitize ANY time between those dates, and contain information about the date.
c. So using a single polygon of 1998-2014 origin is either not appropriate, or requires an uncertainty analysis (which should be included regardless).
d. Also, as detailed by Guo et al. (2017) the first Chinese Glacier inventory was finished in 2002 and covered CGI-1 was compiled based on topographic maps and aerial photographs acquired during the 1950s–80s – so would be a potentially suitable starting outline for you study, then updating to the CGI-2 dating to 2006-2010, compiled by Guo et al. (2017): https://www.cambridge.org/core/journals/journal-of-glaciology/article/second-chinese-glacier-inventory-data-methods-and-results/386DAB512F4869D3335E2DE24B0F43EB
[Response] We note that both you and Reviewer #1 have put forward opinions on the change of glacier areas. In our response to reviewer 1, we explained that we thought uncertainties brought by areas were smaller than uncertainties brought by glacier mass balance (Shean Estimation) so changes in areas of glaciers were not taken into account in this article. However, following your and Reviewer #1’s comments, we will add error analysis on the effect of neglecting areas change.
Thank you very much for providing the article about the second Chinese Glacier Inventory (CGI-2). We learned the CGI-2 was compiled based on 218 remote sensing imageries during 2006-2010 end of ablation seasons using band ratio segmentation method and corrected by field GPS investigation and outlines delineated from high-resolution Google MapsTM images. The CGI-2 (Guo et al., 2015) was the most accurate glacier inventory in China since the 21st century. Based on it, we think about some strategies for analyzing uncertainties about area change of glaciers. Glacier outlines can be obtained from Landsat TM/ETM+ scenes in the two periods (Region1985-1995 and Region1995-2005) in each basin, respectively, in Google Earth EngineTM (hereafter, GEE) based on band ratio segmentation method same as Guo et al. (2015) If scenes are limited by cloud cover or lack of data, we use RGI instead. Kappa coefficient is used to calculate the accuracy of comparison between Region1985-2005 and Google Earth MapTM for each similar scene time. Uncertainties due to area change during 1961-2015 in different basins brought by RGI can be calculated as following equations:
ERGI,i=(ARGI,i-AGEE,i∙Ki)/ARGI,i ×100%
Where ERGI,i is the glacier area error, ARGI,i is the glacier area provided by RGI, AGEE,i is the glacier area calculated by GEE, Ki is the Kappa coefficient between glacier areas calculated by GEE and outlines from Google Earth MapTM, i indicates different basins. And the total glacier area error can be calculated using:
ERGI=√(∑_(i=1)^n▒〖(ERGI,i)〗^2 )
The code of extracting glacier outline in GEE is attached in the supplementary materials. Hope this strategy can solve the problem of uncertainties analysis caused by area change and thanks again for providing references and suggestions.[Reviewer #2 Specific Comment 1] Any use of numbers should spell out the number if below 10, e.g. 7 regions --> seven regions.
[Response] Thanks for your comments and we will exchange the use of numbers below 10 in the whole paper. The corrected sentences read as:
“two goals in the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) (Line 27)
The seven glaciers affect 22 tertiary watersheds in the DAC, including six drainage basins which all originated directly from glaciers and across arid and hyper-arid regions (hereafter, AH). Two river basins were both completely in the arid zone while 11 drainage basins were in both semiarid and arid regions (hereafter, SA). (Lines 102-105)
Based on the RGI 6.0, six glacier regions influence the DAC. (Line 136)”[Reviewer #2 Specific Comment 2] Please use significant digits e.g. L107-108
[Response] We apologize for the unprecise expression. Following your comment, the corrected sentence reads as:
“As Table 1 shows, the area of OAAs in each watershed in the DAC reached a maximum of 21699.18 km2 (Middle Rivers Basin), with an average of 6543.69 km2, while the precipitation in the DAC reached a maximum of 323.09 mm (Qinghai Lake Drainage System), with an average of 134.56 mm, which revealed that runoff in the DAC was extremely important, especially in some basins where runoff originated almost entirely from glaciers.”[Reviewer #2 Specific Comment 3] L15 Is this total annual glacier runoff? Specify time in the sentence or units.
[Response] We are sorry for the unclear sentence. Following your comment, the corrected sentence reads as:
“The total annual glacier runoff in the DAC is (98.52 ± 67.37) × 108 m3 during 1961-2015, in which the meltwater runoff is (63.43 ± 42.17) × 108 m3, accounting for 64.38%.”[Reviewer #2 Specific Comment 4] L29 Add “Glaciers and ice sheets are the….”
[Response] Thanks for your comments. The corrected sentence reads as:
“Glaciers and ice sheets are the largest reservoirs of fresh water on Earth, and they store most of the ice and snow (Beniston & Stoffel, 2014; Kraaijenbrink et al., 2017).”[Reviewer #2 Specific Comment 5] L35 This is not a feedback, it is a one-way relationship, glaciers melt, producing runoff, increasing sea level. These citations do not fit your point.
[Response] Thanks for your comments. As mentioned in response to Reviewer #1’s specific comment 1, what we want to point here is that warming expedites glaciers to melt and then speeds up raising sea levels under current climatic conditions. The increase in meltwater can alleviate drought in the river basins originated from glaciers like the drylands of China, but sea level rise poses risks to coastal areas, meaning that the meltwater of glaciers is not only a result of climate change but also contributing to the consequences of climate change such as rising sea levels. So, we think we could change the sentence and references as follows:
“Under current climatic conditions, warming expedites glaciers to melt and meltwater speeds raising sea levels, which is why glaciers are both the result of and contributor to climate change.”[Reviewer #2 Specific Comment 6] L51-57 The problem is not clearly stated here. You state that “Continuous yearly mass balance data for long time series could not be calculated effectively due to the time consumption and high energy consumption of field observations (Brun et al., 2017; Shean et al., 2020).” This is poorly worded and incorrect. Long time series cannot be calculated because the data don’t exist, which in turn is because field observations are logistically and financially difficult.
[Response] We are sorry for the unclear statement. We intended to express that the financial and logistic difficulties of field observations result in the lack of long-time series in regional scales. Thank you very much for your comment so we will amend this sentence to read as:
“Continuous yearly mass balance data for long time series in regional scales could not be calculated effectively due to the financial and logistic difficulties of field observations (Brun et al., 2017; Shean et al., 2020).”[Reviewer #2 Specific Comment 7] L62 Two problems here, one, this is an incomplete sentence, and further, why is the resolution so low? Perhaps because the data are not sufficient to use at finer resolutions? “…while the energy balance model could be applied in 62 large regions but with low resolution (such as 0.25 degrees (Sakai et al., 2015))”.
[Response] We are sorry for the incomplete sentence. In this sentence, we wanted to express two messages. First, we wanted to indicate that the relationship between the recorded data of meteorological stations based on the degree-day factor model and glacier runoff cannot be applied in regional scales limited by the distribution of meteorological stations (Duan et al., 2017). Second, although Sakai et al. established the map of ELA in regional scales, the resolution was low with 0.5 degrees, which could not be applied in scales of basins proposed in this paper. Sakai et al. derived Asian glaciers from the Glacier Area Mapping for Discharge in Asian Mountains (GAMDAM) glacier inventory (GGI) (Nuimura et al., 2015) to evaluate the clime regime at high-mountain Asia. While the GGI occupied the grids of glacier regions as 0.25 degrees and datasets used such as ERA-Interim reanalysis data – including temperature (level), surface wind (surface flux 10m), surface humidity (surface), and solar radiation (surface flux) - from 1952 to 2007, and APHRODITE from 1952 to 2007 was at a spatial resolution of 0.75 degrees and 0.50 degrees, respectively, so Sakai’s paper was with a resolution of 0.50 degrees. Following your comment, the modified sentence and references read as:
“However, limitations were obvious. Establishing the relationship between stations and the degree-day factor model was too difficult in large regional scales limited by numbers and the distribution of meteorological stations (Duan et al., 2017). Also, the energy balance model could be applied in large regions but limited by resolution for multiple datasets (Sakai et al., 2015).”[Reviewer #2 Specific Comment 8] L99 erased the range?
[Response] While using the aridity index to zone arid regions, the Qinghai-Tibet Plateau will be included in arid areas. Due to the specificity of the Qinghai-Tibet Plateau, our team thinks the area should be studied separately. Therefore, the arid zone used in this paper excludes the Qinghai-Tibet Plateau. Following your comment, the corrected sentence reads as:
“The region of DAC was obtained relying on aridity index supported by the United Environment Programme (UNEP) excluding the range of the Tibetan Plateau which should be discussed separately because of its particularity.”[Reviewer #2 Specific Comment 9] L102 7 glaciers? Or 7 glacier regions?
[Response] We are sorry for the wrong expression. The modified sentence reads as:
“The seven glacier regions affect 22 tertiary watersheds in the DAC, including six drainage basins which all originated directly from glaciers and across arid and hyper-arid regions (hereafter, AH).”[Reviewer #2 Specific Comment 10] Figure 1 Font is too small in axes and legend (commonly in many figures)
[Response] Following your comment, we make fonts in each figure larger to make it easier for readers.[Reviewer #2 Specific Comment 11] L122-123 Doesn’t make sense. You are implying that you did the work of Shean et al. (2020).
[Response] Thanks for your comment. This sentence is meant to introduce how Shean et al. (2020) obtained the mass balance dataset. Following your comment, the modified sentence reads as:
“We used regional available glacier mass balance dataset to correct high-altitude precipitation.”[Reviewer #2 Specific Comment 12] L126-148 Way too long of a description of these studies, if you want to show the comparison in lines 136-145, use a table, this is hard to read.
[Response] Thanks for your comment, we are going to illustrate this comparison using a table attached in supplementary materials. The table is attached at the end of this response.[Reviewer #2 Specific Comment 13] L267 Blocks represent modules (add the s)
[Response] Thanks for your careful reading. The corrected sentence reads as:
“Fig. 2. Conceptual framework of glacier runoff calculating. Blocks represent modules of 267 the glacier runoff calculation in each category. Shading indicated results with uncertainties and different lines and blocks indicated the corresponding modules.”[Reviewer #2 Specific Comment 14] L289-290 “and we overcame the difficulty of large-scale geodetic mass balance assessment” What? Brun et al. (2017) and Shean et al. (2020) did this.
[Response] We are sorry for the wrong expression. The corrected sentence reads as:
“In this paper, Shean Estimation was used to reconcile high-altitude precipitation. The yearly mass balance of glaciers influencing the DAC from 1961 to 2015 was calculated by the difference between accumulation obtained from corrected precipitation and ablation calculated by the DDF model. A long-time series dataset of total glacier runoff dataset including delayed runoff and meltwater runoff based on temperature was created, which was at large regional scales with a spatial resolution of 100 m. It is important to note that glacier runoff in this paper means runoff generated within the geographical area of a glacier”[Reviewer #2 Specific Comment 15] L300-301 “The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin”, wouldn’t the opposite be true? Delayed runoff is not directly from glacier wastage (stored seasonal precip), so is more sustainable than ice wastage.
[Response] As mentioned in Response to Reviewer #1’s specific comment 17, Kriya Rivers Basin is special where 93.67% of glacier runoff comes from delayed runoff. It could be said that delayed runoff is basically determined by rainfall and temperature, which is distinguished from meltwater runoff. Therefore, when extreme precipitation climate occurs, it is easy to cause geologic hazards such as flash floods which should be paid attention to (Kaltenborn et al., 2010; Shen et al., 2004). The hazards here are more related to extreme rainfall than with the glaciers themselves. But referring to your and Reviewer #1’s comment and some references, we think Kashgar River basin, Hotan River basin, and Yarkand River basin should be paid more attention to because delayed runoff and meltwater runoff account for a certain proportion in each basin. The combination of extreme precipitation and rapid snow melting would increase runoff in glacier areas and make them more prone to disasters. The corrected sentence reads as:
“The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components coming from delayed runoff. More attention should be paid to Kashgar River basin, Hotan River basin, and Yarkand River basin where delayed runoff and meltwater runoff account for a certain proportion and annual total glacier runoff was large. While extreme precipitation happened with rapid snow melting, glacier runoff would increase in haste to make these basins more prone to disasters (Kaltenborn et al., 2010; Shen et al., 2004).”[Reviewer #2 Specific Comment 16] Figure 3 Units on runoff?? The legend just says “5.6”. How useful are raw runoff numbers versus percent contributions of total river discharge?
[Response] We are sorry for the unclear legend in Figure 3. The “5.6” represents that the longest column in the legend was 5.6×108 m3. We will correct our figures to make them more clearly. The percentage of glacier runoff relative to total river discharge is helpful to distinguish water sources and provide some references for water allocation after glacier shrinkage under climate change in the future.[Reviewer #2 Specific Comment 17] L323-338 Replace most this paragraph with a table and reference that table with a few lines.
[Response] Thanks for your comment and we simplify the description with tables to make it easier for readers to understand.
[Reviewer #2 Specific Comment 18] L324 Glaciers should be lowercase.
[Response] Thanks for your comment. The corrected sentence reads as:
“From 1961 to 2015, glaciers in the arid regions provided (63.43 ± 42.17) × 108 m3 of glacial excess meltwater.”References:
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AC3: 'Supplementary Reply on RC2 (Methods and Glacier Area Change)', Xuejing LENG, 22 Nov 2021
Thanks again for your helpful and valuable comments on our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). After studying your comments carefully, we have made some corrections which we hope to meet with approval.
- First of all, we rewrite the Methods and annotate parameters correctly. As for some details we have discussed too much, such as the reasons for choosing Shean Estimation and APHRODITE, we use charts and figures to illustrate them in supplementary materials. We also add the methods to calculate the glacier area change. The revised Methods with supplementary materials are attached in the supplement.
- We add the analysis of changes in glacier areas. Glacier outlines were extracted from Landsat TM scenes in the two periods (Region1985-1995 and Region1995-2005) in each basin at the end of ablation seasons (September to November), respectively, in Google Earth EngineTM (hereafter, GEE) based on band ratio segmentation method (Guo et al., 2015; Paul et al., 2009; Racoviteau et al., 2009). The distribution of different sizes in different basins is shown in the supplements. We also add an analysis of changes in glacier area in Results.
Hope the revised version meets your requirements.
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AC2: 'Reply on RC2', Xuejing LENG, 14 Nov 2021
Status: closed
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RC1: 'Comment on hess-2021-377', Anonymous Referee #1, 25 Oct 2021
Review HESS The spatiotemporal regime of glacier runoff in oases indicates the potential climatic risk in dryland areas of China
This manuscript calculates timeseries of glacier runoff for the dryland areas of China for the period 1961 until 2015 using the APHRODITE gridded precipitation and temperature products. These estimates of glacier runoff are used to indicate the amount of glacier meltwater that comes from the imbalance and balance component of glacier runoff (referred to as meltwater runoff and delayed runoff, respectively, in the manuscript) and to analyze trends. In the discussion section the amount of glacier runoff is compared with some estimates of the agricultural, industrial and municipal water consumption. All of the analyses are done for 22 basins in the northwestern part of China.
Although the title of this study sounds interesting and could potentially be of interest for HESS, I found this first impression not reflected in the content of the rest of the manuscript. First of all, the poor writing and unfinished or wrong sentence structures make it at many places impossible to understand what actually has been done. Regardless of the writing, the methods are described in a very unsystematic way and many details are missing. Furthermore, I had troubles identifying the added value of this study. The study uses several different existing datasets to calculate annual glacier runoff, which is according to the study a novelty compared to the multi-year mean geodetic mass balances. However, it does not become clear which question(s) can be answered with these annual glacier runoff estimates. A clear link to other terms in the water balance of these oases regions is missing, or a discussion how water from the glaciers reaches the agricultural areas. I even doubt the usefulness of calculating trends if changes in glacier extent are not considered. Overall, I cannot recommend publication of this study. Please find below a few more comments.
P2: ‘Under current climatic conditions, warming causes glaciers to melt and sea level to rise, creating a negative feedback between the two’ -- what is the negative feedback here?
P3: ‘Semi-distributed hydrological models semi-quantitively calculated the proportion of meltwater runoff to total runoff without time series’ -- what is meant with ‘without time series’?
P4: ‘Dataset of spatial distribution of degree day factors for glaciers’ -- since this dataset is so central for the calculations in this study, just giving a link to this data is not acceptable
P5: The table shows the area of the oases in each watershed. Apart from expecting here instead the relative area of OAA and glacier cover, the amount of rain in mm does not give a lot of information on the importance of glacier runoff. Why is glacier runoff not calculated as mm/y?
P7-15 Methods:
A whole page is used to describe different studies and data sources of geodetic mass balances, first describing that two datasets will be compared (Brun and Shean), to later read only the ‘Shean estimation’ is used.
The resolution is 100 m. What does this mean? How does the DDF vary in space? Are the PDD or PDDm calculated for each glacier, for each 100 m, for each basin?
How was the maximum rainfall height determined?
From the description in the manuscript it is also unclear how the precipitation gradient was optimized. Was the ablation calculated based on the same period as the Shean mass balance estimation? And what is ‘H’, the mean elevation of the glacier? In the current formula (equation 4), the elevation between Hmax and Hmap are taken twice into account? Or did I understood something wrong? Should it not be (- delta H)? Why were the vertical gradients interpolated if they are already calculated for each individual glacier?
Like in other parts of the paper, also here discussion parts are mixed up with the methods part and it is confusing to read again about the precipitation gradients in section 2.3.2.
Regarding the uncertainty analyses, what is meant with ‘the PG of each single glacier around the DAC was obtained with geographical simulation’? In a few paragraphs before I read that PG was obtained by fitting the accumulation to the geodetic mass balance and estimated ablation? And why is only the uncertainty in the Shean mass balance estimation considered? What is the uncertainty in the DDF? These can have a large effect also on the accumulation estimates.
For the calculation of glacier runoff and consequently the trend analyses, I do not understand what is meant with the 100 m resolution of this study and how changing glacier area is considered. Are precipitation and temperature calculated for fixed grid cells containing the glacier? Which of the parameters are changing over time to calculate a trend in the glacier runoff? Changes in P and T can affect the total glacier runoff and the partitioning between balanced and imbalanced contributions, but also the changes in glacier extent play a role for the amount of glacier runoff.
P15: ‘The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components (glacier runoff) coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin. What is meant here?
Why is 3.2 a results section? It rather discusses the results? the 3.2 on P18, there is also a 3.2 on P23.
What is the point that the study tries to make in Section 4.1 and 4.2? From the methods section the calculation of the precipitation gradient was already unclear, but the discussion section does not clarify any of these concerns. Hmap and Href are the same? Could the ‘believing’ in one or two maximum rainfall heights not be demonstrated here?
Section 4.3 does in my point of view not add anything to the study.
Regarding section 4.4, it is described that oases in the DAC rely most on glacier runoff and that it maintains soil moisture, vegetation growth and groundwater replenishment. However, without comparing glacier runoff to other sources of water and without describing the pathways of glacier runoff (how does glacier melt become soil moisture?), such conclusions cannot be drawn.
P33: ‘For example, due to increased temperature and reduced glacier runoff, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds’ -- I think such a statement requires a reference. Moreover, a lack of precipitation and snowmelt and increased evaporation caused a severe drought, rather than the small ‘reduced glacier runoff’ contribution.
P33: ‘In the future, glacier runoff will reach its peak when glacier tourism disappears’ -- What is the connection between these two processes?
P34: The linear regression is only introduced in the conclusion (I could not find it elsewhere in the manuscript). Apart from that, how does the study deal with the non-linear change in glacier runoff (peakwater)?
P34: Nothing that is mentioned at point three in the conclusion I can find in the results section. Where do these conclusions come from?
Citation: https://doi.org/10.5194/hess-2021-377-RC1 -
AC1: 'Reply on RC1', Xuejing LENG, 03 Nov 2021
Thank you very much for providing the insightful comments for our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). First of all, we realize that there were many unclear expressions and wrong marks of parameters in the manuscript which confused you. Following your comments, we have modified the corresponding sentence in responding to each specific comment. We will ask a well-established expert to polish our paper in the revised manuscript. According to your all comments, we think the main corrections in the paper are as follows:
- Correct the wrong variable expression in Method (such as ), and put discussion about precipitation dataset and mass balance dataset into supplementary materials and present it in figures or charts.
- For the socio-economic results of glacier runoff, a specific analysis of the impacts of glacier runoff on oases (e.g. using hydrological models) can be supplemented to increase the persuasiveness of this paper.
As for the method part, we think that adjusting the overall narrative structure is useful to express our method more systematically and explain each variable clearly. The revised method part will be 1. Reconciling High-altitude 2. Glacier Runoff and 3. Uncertainty analysis. There are indeed some confusing parts in the method part, such as the comparison of mass balance datasets (lines 124-144). We may change this section into a figure in the supplementary materials attached to the manuscript. However, as precipitation is the most basic link in the water cycle and the most basic element in the whole calculation process, we believe that the reasons for selecting precipitation data need to be further explained and verified. Therefore, we only embellished the language in this part but did not delete the two paragraphs (lines 195-224). The confusing concluding paragraph (lines 251-254) should be deleted, and the methods section should now be clear and not short of details. Thank you again for your guidance.
As pointed in the introduction part (lines 61-68), energy balance models which commonly used in calculating glacier runoff are with low resolution and other physical models perform weak on regional scales. Most studies focus on single glacierized catchments or glacier, or develop corresponding glacier runoff modules in areas where terrestrial observations are abundant. In this paper, a high-resolution calculation method of glacier runoff is developed on a regional scale and be applied in oasis regions in drylands of China to answer the hydrological consequences of glacier runoff, for example, the proportion of water withdrawn in oases due to glacier runoff including delayed runoff and meltwater runoff, in these vital basins in arid areas. Because of our unreasonable words’ allocation in the introduction and application, you may not understand the meaning of this research. Highlight the gap that poor research about high-resolution glacier runoff calculating on regional scales may improve readers’ recognition of this research.
For the doubt “missing a discussion how water from the glaciers reaches the agricultural areas”, we obtained the catchment regions as shapefiles from the RESDC (Resource and Environment Science and Data Center of the Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences) on public (lines 89-91). Basins with oases in our article are all originated from glaciers so glacier runoff is bound to affect those oases. While our article focuses on high-resolution glacier runoff calculating on regional scales but not the hydrological distribution model, the accurate value arrived at the oases (how water reached) is not our goal in this paper. We think that the changing proportion of water withdrawals due to glacier runoff under clime change is sufficient to illustrate the threat of glacier runoff to oases. However, following your comment, we think adding a case in one glacier basin to explain the socio-economic consequence caused by glacier runoff will make this paper more persuasive.
The suspicion “the usefulness of calculating trends if changes in glacier extent are not considered” appeared is because the scarce introduction of the glacier extent datasets (lines 87-88, Information about glacier outlines, elevations, and areas was derived from the Randolph Glacier Inventory (version 6.0, https://www.glims.org/RGI/rgi60_dl.html)). Randolph Glacier Inventory, a multisource glacier inventory (lines 145-148), was obtained by overlaying outlines on modern satellite imagery and aggregating the World Glacier Inventory. All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time. Two methods are to use widely to identify changes in glacier extent. One is used the MOD10A1 Snow Cover Daily Global 500m product based on a snow mapping algorithm employing the NDSI (Normalized Difference Snow Index) to obtain the changing of glacier extents (Hall et al., 2016; Muhammad and Thapa, 2021). However, we think that glacier extents changes over the past 55 years cannot be accurately expressed by a 500m product. The other is using satellite imageries in a resolution of 30 m and also the NDSI (Wang et al., 2020; Tak and Keshari, 2020). But the extent is not be as of accurate as the glacier inventory like RGI because of the difficulties to select the least-cloudy scenes. So, we chose the multisource glacier inventory RGI for our research. In addition, we verified our glacier runoff in section 3.2 Glacier Runoff validation testifying our trends over Aksu River Basin (1961-1986, lines 402-405) and Ebinur Lake Drainage Systems (the 1980s, lines 406-407) to be usable even if before 1990. Based on the former uncertainties about obtaining changing glacier extents, we think RGI is the most appropriate while the calculation results are proved to be consistent even in the time before the inventory was constructed (1961-1990), so trends can also be used to indicate changes in local glacier runoff.
Overall, thank you for your doubts and suggestions on our language, method structure, and some narrative details, which make great progress on our research. We still insist that the research is valuable. As oases’ special impacts supporting agriculture, industry, and municipality in arid areas, how much relative stable water is provided by glaciers is a vital problem to be solved. This paper can fill in the gap of glacier runoff calculation on regional scales lack of local terrestrial observations. However, a case of how much glacier runoff arrived oases is needed to add to the discussion section.
Through the above explanation, I hope you can understand the purpose and hope to dispel your doubts.
A detailed point-by-point response to each comment is shown followed and we think the article will be more persuasive after our discussion.
[Reviewer #1 Specific Comment 1] P2: ‘Under current climatic conditions, warming causes glaciers to melt and sea level to rise, creating negative feedback between the two’ -- what is the negative feedback here?
[Response] Following this comment, we apologize for our unclear expression. What we want to point is that warming expedites glaciers to melt and then speeds up raising sea levels under current climatic conditions. The increase in meltwater can alleviate drought in the river basins originated from glaciers like the drylands of China, but sea level rise poses risks to coastal areas, meaning that the meltwater of glaciers is not only a result of climate change but also contributing to the consequences of climate change such as rising sea levels. So, we think we could change the sentence as follows:
“Under current climatic conditions, warming expedites glaciers to melt and meltwater speeds rising sea levels, which is why glaciers are both the result of and contributor to climate change.”
[Reviewer #1 Specific Comment 2] P3: ‘Semi-distributed hydrological models semi-quantitively calculated the proportion of meltwater runoff to total runoff without time series’ -- what is meant with ‘without time series’?
[Response] The semi-distributed hydrological models used in the previous study only semi-quantitatively calculated the proportion of meltwater runoff to the total runoff. For example, Wang et al. (2019) calculated that glacier runoff accounted for 24.4% of the total runoff in combination with the hydrological data of the outlet in the Ebinur Lake Drainage System. Gao et al. (2008) calculated that glacier runoff in the Kai-Kong River Basin accounted for 21.1% in the 1980s and 22.1% in 2000 or the total runoff, respectively. What these researches showed are ratios over time and but not illustrating complete glacier runoff time series, so we say they are ‘without time series’. Perhaps the expression in the original text is not clear enough, we think adding some examples at the end of this sentence for further modification to explain can solve the problem. The corrected sentence is as follows:
“Semi-distributed hydrological models semi-quantitively calculated the mean proportion of glacier runoff to total runoff rather than a time series, such as 21.1% in the Kai-Kong River Basin in the 1980s (Gao et al., 2008) and 24.4% in the Ebinur Drainage System (Wang et al., 2019).”
[Reviewer #1 Specific Comment 3] P4: ‘Dataset of spatial distribution of degree day factors for glaciers’ -- since this dataset is so central for the calculations in this study, just giving a link to this data is not acceptable
[Response] Following this comment, we think that the explanation of this dataset is not obvious enough that we just describe how the dataset is established in our manuscript (Lines 153-155, ‘This paper used the spatial distribution of snowmelt data with a resolution of 0.5° based on a formula built by investigations and observations of 40 different glaciers in the HMA, and the dataset verified the accuracy (Zhang et al., 2006).’). We will correct the unclear sentence and add validation about this dataset in the corrected manuscript as follows:
“This paper used the spatial distribution of degree-day factors (DDFs) for glaciers with a resolution of 0.5° based on a formula built by investigations and observations of 40 different glaciers in the HMA. Map of isolines for the DDFs shows the factors increase gradually from northwest to southeast in western China which is consistent with the varied climatic environment from cold-dry to warm-wet (Zhang et al., 2006).”
[Reviewer #1 Specific Comment 4] P5: The table shows the area of the oases in each watershed. Apart from expecting here instead the relative area of OAA and glacier cover, the amount of rain in mm does not give a lot of information on the importance of glacier runoff. Why is glacier runoff not calculated as mm/y?
[Response] The average annual precipitation (mm/y) for each basin of dryland areas of China is listed in Table 1 to show the spatial precipitation heterogeneity between basins. The intention is to illustrate the scarcity and instability of precipitation in the arid zone and to highlight the importance of glacier runoff providing a relatively stable water amount. The table only provides the average annual precipitation as mm/y, but following this comment, we think we should add the coefficients of variation of precipitation to indicate different water conditions in the study area. Explaining the heterogeneity then readers could understand the effects of glacial runoff on mitigation of water scarcity in arid areas. We used mm/y as the unit of precipitation under the description of precipitation in previous studies, while m3 is used as the unit of glacier runoff to highlight the amount of glacier runoff and facilitate numerical comparison with the amount of agricultural, industrial, and municipal water consumption. According to AQUASTAT (FAO's Global Information System on Water and Agriculture, https://www.fao.org/aquastat/en/), the unit of water withdrawal by sector in different countries is m3. However, we apologize for the lack of pointing out the water withdrawal source. We will add the part as follows:
“The data used in our manuscript is from AQUASTAT (https://www.fao.org/aquastat/en/), The agricultural water consumption at the watershed scale was obtained by averaging the agricultural water consumption statistical data to the land use types of agricultural land and then ranged regional statistics, which was the same with industrial and municipal water consumption.”
[Reviewer #1 Specific Comment 5] P7-15 Methods: Methods:
A whole page is used to describe different studies and data sources of geodetic mass balances, first describing those two datasets will be compared (Brun and Shean), to later read only the ‘Shean estimation’ is used.
[Response] In section 2.3.1 Reconciling High-altitude Precipitation, we first compare the calculation results of mass balance by Brun et al. and Shean et al. using ASTER DEMs and by IceSat-1 (Ice, Cloud, and land Elevation Satellite) in High-mountain Asia. The comparisons are shown in Lines 126 to 131. Since the IceSat-1 datasets were used to calculate the elevation changes of glaciers larger than 5 km2 not reflecting smaller glaciers and ended proving data in 2009, we choose not to use this dataset in our research (Lines 131-134). Excluding IceSat-1 dataset, this paper focused on comparing the Shean Estimation and Brun Estimation to handle a more appropriate dataset. We compare these two datasets in each region of glaciers in dryland areas of China, and point out the main estimates between the two datasets were relatively consistent, but there was a big difference between the uncertainties (Lines 137-145). This is because the Brun Estimation was a mass balance raster dataset with a spatial resolution of 30 m while Shean Estimation calculated the mass balance of each glacier in the RGI (Randolph Glacier Inventory) and for the above reasons, we select Shean Estimation (Lines 145-148). Since the glacier mass balance dataset is a key dataset for this paper's input data, we thought it should take a whole page to explain why we chose this dataset (Shean Estimation) over others (IceSat-1 or Brun Estimation). We apologize for the confusion in this paragraph and for not giving the reader a clear understanding of why we chose Shean Estimation. To explain more clearly why we choose Shean Estimate, we can change this part into a graphic description in the supplementary materials attached to the manuscript, and simplify the description of the mass balance dataset comparisons.
[Reviewer #1 Specific Comment 6] P7-15 Methods: Methods:
The resolution is 100 m. What does this mean? How does the DDF vary in space? Are the PDD or PDDm calculated for each glacier, for each 100 m, for each basin?
[Response] We apologize for the unclear sentence “Considering that the spatial resolution of this paper was 100 m, monthly positive-degree days ( ) were chosen instead of absolute (Braithwaite & Olesen, 1993), and they were the summed positive daily average temperatures.” (Lines 155-157). Map of isolines for the DDFs shows the factors increase gradually from northwest to southeast in western China which is consistent with the varied climatic environment from cold-dry to warm-wet ((http://www.sciencedb.cn/dataSet/handle/747). The spatial pattern of DDF in High-mountain Asia will be added later (see the response for Specific Comment 3). The PDD is calculated at a spatial resolution consistent with other variables on the 100 m grid scale. The temperature of PDD is calculated according to the APHRODITE data corrected by DEM data, that is, the temperature decreases by 0.65 degrees for every 100 m rise. So, the corrected sentence reads as:
“Monthly positive-degree days ( ) were chosen instead of absolute (Braithwaite & Olesen, 1993) while the calculation method was still summing positive daily average temperatures, on the 100 m grid scale. The temperature was obtained according to the APHRODITE data corrected by DEM data, that is, the temperature decreases by 0.65 degrees for every 100 m rise.”
[Reviewer #1 Specific Comment 7] P7-15 Methods: Methods:
How was the maximum rainfall height determined?
[Response] As the name suggests, the height where rainfall is the largest in the whole section is generally called the maximum rainfall height. A detailed discussion of the maximum rainfall height is presented in section 4.1 Precipitation Correction at High-altitudes (lines 495-543). In the part, we compare the debate between glaciologists and meteorologists about the maximum rainfall height. There has always been controversy over whether there are one or two maximum altitudes in the mountains. Even in the same region, there are different results due to the limitations of the discipline, purpose, method, time, or initial conditions of the study. About this controversy, we have introduced it in detail in the discussion section (lines 495-543).
[Reviewer #1 Specific Comment 8] P7-15 Methods: Methods:
From the description in the manuscript, it is also unclear how the precipitation gradient was optimized. Was the ablation calculated based on the same period as the Shean mass balance estimation?
[Response] The ablation was calculated by the product of and as shown in lines 157-158. The original sentence reads as:
“The monthly spatial distribution of ablation, (m), was calculated by the product of and when the sum of the twelve months was the yearly spatial distribution of ablation, it is (m).”
[Reviewer #1 Specific Comment 9] P7-15 Methods: Methods:
And what is ‘H’, the mean elevation of the glacier?
[Response] The variable ‘H’ is the terrain elevation for each glacier described in line 169 meaning the mean terrain elevation calculated by DEM for each glacier.
[Reviewer #1 Specific Comment 10] P7-15 Methods: Methods:
In the current formula (equation 4), the elevation between and are taken twice into account? Or did I understand something wrong? Should it not be (- delta H)？
[Response] We must apologize for the mistakes in Equation (3) and Equation (4). The correct equations are:
∆H=H-Hrmd (3)
P(cor,d)=P(rmd,d)∙{1+[∆H+(H-Hmap)]} (4)
△H was calculated by the mean terrain elevation from DEM minus DEM aggregated into the same scales as the APHRODITE dataset, Hrmd (m), for each glacier affecting the DAC. And the corrected precipitation, P(cor,d) (m), was calculated as a function of original precipitation data from APHRODIE_MA_v1101_EXR1, P(rmd,d) (m), the vertical precipitation gradient, PG (% m-1), at a daily time step with the maximum rainfall height, Hmap (m) and mean terrain elevation from DEM, H (m), for each glacier.
[Reviewer #1 Specific Comment 11] P7-15 Methods: Methods:
Why were the vertical gradients interpolated if they are already calculated for each individual glacier?
[Response] As the spatial resolution of temperature and precipitation dataset from APHRODITE is 0.25°, which is quite different from the area of glaciers, the vertical precipitation gradient between nearby glaciers may be quite different. Interpolating each glacier’s precipitation gradient could smooth the errors caused by the boundary of the raster data.
[Reviewer #1 Specific Comment 12] P7-15 Methods: Methods:
Like in other parts of the paper, also here discussion parts are mixed up with the methods part and it is confusing to read again about the precipitation gradients in section 2.3.2.
[Response] In section 2.3.1 Reconciling High-altitude Precipitation, we introduce how to calibrate precipitation data through glacier mass balance dataset. We compare the IceSat-1, Brun Estimation, and Shean Estimation to select a more appropriate dataset for our paper (lines 124-148). The degree-day model is used to calculate glacier ablation (lines 150-158). The way to calculate glacier accumulation (corrected precipitation in this paper) is shown in Equation (2) on each glacier is calculated according to the corrected temperature data based on altitude. Then put the result of Equation (2) in Equation (3) and Equation (4), the vertical rainfall gradient could be calculated. And interpolate precipitation gradient to reduce the error caused by grid edge mutation.
[Reviewer #1 Specific Comment 13] P7-15 Methods: Methods:
Regarding the uncertainty analyses, what is meant with ‘the PG of each single glacier around the DAC was obtained with geographical simulation’? In a few paragraphs before I read that PG was obtained by fitting the accumulation to the geodetic mass balance and estimated ablation?
[Response] As mentioned before, we use interpolation to reduce the uncertainty caused by data mutation at a spatial resolution of 0.25 degrees. So, the geographical simulation here refers to the interpolation method. We apologize for our unclear statement. The sentence needs to be corrected as follows:
“The PG of every glacier around the DAC was obtained by combining the accumulation of mass balance and ablation calculated by degree-day factor model, and geographical simulation was used to reduce the impact of data mutations.”
[Reviewer #1 Specific Comment 14] P7-15 Methods: Methods:
And why is only the uncertainty in the Shean mass balance estimation considered? What is the uncertainty in the DDF? These can have a large effect also on the accumulation estimates.
[Response] According to the individual glacier uncertainty (including random error and systematic error) calculated in the Shean Estimation, we calculated the uncertainty of mass balance. We agree that the uncertainty in the DDF can also bring a large effect on the results. However, previous studies used degree-day factors as a constant value, which means, degree-day factor for glaciers was (2±2) (mm ◦C−1 d−1). The DDF we used in this paper is from the map of degree-day factors for glaciers in High-mountain Asia which was built by investigations and observations of 40 different glaciers. This distribution of DDF has improved the accuracy when DDF is just a constant value (2±2) (mm ◦C−1 d−1), so the uncertainty of DDF is not considered as a calculation in this paper.
[Reviewer #1 Specific Comment 15] P7-15 Methods: Methods:
For the calculation of glacier runoff and consequently the trend analyses, I do not understand what is meant with the 100 m resolution of this study and how changing glacier area is considered. Are precipitation and temperature calculated for fixed grid cells containing the glacier?
[Response] The spatial resolution with 100 m was chosen because of the spatial resolution of DEM (version4.1, http://srtm.csi.cgiar.org). We uniformly resampled the precipitation, temperature, and DDF to the spatial resolution of 100 m using the nearest neighbor method before all the calculations in this paper.
[Reviewer #1 Specific Comment 16] P7-15 Methods: Methods:
Which of the parameters are changing over time to calculate a trend in the glacier runoff? Changes in P and T can affect the total glacier runoff and the partitioning between balanced and imbalanced contributions, but also the changes in glacier extent play a role for the amount of glacier runoff.
[Response] The variables needed to calculate glacier runoff include altitude, precipitation, degree-day factor, and temperature, and of which precipitation and temperature are two major variables over time. The altitude is from DEM and the DDF is from the map of degree-factor in HMA which was built by 40 observations rather than a constant value. Randolph Glacier Inventory, a multisource glacier inventory (lines 145-148), was obtained by overlaying outlines on modern satellite imagery and aggregating the World Glacier Inventory. All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time. Two methods are to use widely to identify changes in glacier extent. One is used the MOD10A1 Snow Cover Daily Global 500m product based on a snow mapping algorithm employing the NDSI (Normalized Difference Snow Index) to obtain the changing of glacier extents (Hall et al., 2016; Muhammad and Thapa, 2021). However, we think that glacier extents changes over the past 55 years cannot be accurately expressed by a 500m product. The other is using satellite imageries in a resolution of 30 m and also the NDSI (Wang et al., 2020; Tak and Keshari, 2020). But the extent is not as accurate as of the glacier inventory like RGI because of the difficulties to select the least-cloudy scenes. So, we chose the multisource glacier inventory RGI for our research. In addition, we verified our glacier runoff in section 3.2 Glacier Runoff validation testifying our trends over Aksu River Basin (1961-1986, lines 402-405) and Ebinur Lake Drainage Systems (the 1980s, lines 406-407) to be usable even if before 1990. Based on the former uncertainties about obtaining changing glacier extents, we think RGI is the most appropriate while the calculation results are proved to be consistent even in the time before the inventory was constructed (1961-1990), so trends can also be used to indicate changes in local glacier runoff.
[Reviewer #1 Specific Comment 17] P15: ‘The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components (glacier runoff) coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin. What is meant here?
[Response] The composition of glacier runoff in the Kriya Rivers basin is special compared with other river basins where 93.67% of glacier runoff comes from delayed runoff. Delayed runoff is the part runoff stored in glacial areas during cold seasons and then is released in the warm season. It could be said that delayed runoff is basically determined by rainfall and temperature, which is distinguished from meltwater runoff. Therefore, when extreme precipitation climate occurs, it is easy to cause geologic hazards such as flash floods which should be paid more attention to (Kaltenborn et al., 2010; Shen et al., 2007).
[Reviewer #1 Specific Comment 18] Why is 3.2 a results section? It rather discusses the results? the 3.2 on P18, there is also a 3.2 on P23.
[Response] We apologize for the wrong subheadings in Section 3 Results. The correct subheadings are 3.1 Glacier Runoff during 1961-2015 on P15, 3.2 Glacier Runoff validation on P18, 3.3 Glacier Classification Based on Potential Climatic Risks on P23, and 3.4 The Spatiotemporal Change in Glacier Runoff on P24. We first show the calculated glacier runoff values in the Results, and then verify the calculated glacier runoff. As the data are reliable, we explain the climate risk and the temporal and spatial characteristics of glacier runoff including delayed runoff and meltwater runoff. The discussion section includes some detailed discussions of calculating methods and supplements of the socio-economic impact of glacial runoff on oases.
[Reviewer #1 Specific Comment 19] What is the point that the study tries to make in Section 4.1 and 4.2? From the methods section the calculation of the precipitation gradient was already unclear, but the discussion section does not clarify any of these concerns. Hmap and Href are the same? Could the ‘believing’ in one or two maximum rainfall heights not be demonstrated here?
[Response] Our intention in section 4.1 is to discuss the concept of maximum rainfall height and the different maximum rainfall heights for each region, as well as the debate among meteorologists (lines 507-513) and glaciologists (lines 496-503) about maximum rainfall height. And because of different data or observing methods used, the maximum rainfall height would be different even in the same district (lines 515-529). After these descriptions, Table 2 shows the maximum rainfall height for each region used in this paper. In 4.2 of the discussion section, we want to illustrate the calculated distribution of precipitation gradient (PG) in seven glacier regions (Eastern Tien Shan, Western Tien Shan, Eastern Kunlun, Western Kunlun, Pamir, Qilian Shan, and Karakoram) and the statistical results of PG at different elevation ranges (△H+(H-Hmap), where △H=H-Hrmd). We apologize for the misrepresentation of Equation (3) and Equation (4) again. As a result of this error, the abscissa heading on the left-hand chart in Figure 8 is also incorrect. There is no Href variable in the paper, only maximum rainfall height, Hmap.
As for the debate about whether there are one or two rainfall heights, this paper cannot demonstrate. Equation (3) and Equation (4) in this paper are based on the hypothesis that there is only one maximum rainfall height in a mountain. Corrected high-altitude precipitation decreases with a certain precipitation gradient (PG) corresponding to the height above the only maximum rainfall height. While we have chosen "one rainfall height" as the calculation basis, we think the basis cannot be verified by the conclusions generated on this basis.
[Reviewer #1 Specific Comment 20] Section 4.3 does in my point of view not add anything to the study.
[Response] Our intention in section 4.3 is to explain the rationality of selecting precipitation and temperature as input variables for the calculation of glacier runoff as mentioned in lines 570-572. While glaciers in High-mountain Asia are all continental glaciers, precipitation and temperature are the two major factors of glacier runoff change. Frontal ablation is not considered because glaciers regions in this paper are all continental glaciers. Section 4.3 also shows that, compared with precipitation, the temperature is a more dominant influencing factor in the glacier regions studied in this paper (Azam & Srivastava, 2020; Ban et al., 2020; Huai, 2020; Noël et al., 2020).
[Reviewer #1 Specific Comment 21] Regarding section 4.4, it is described that oases in the DAC rely most on glacier runoff and that it maintains soil moisture, vegetation growth and groundwater replenishment. However, without comparing glacier runoff to other sources of water and without describing the pathways of glacier runoff (how does glacier melt become soil moisture?), such conclusions cannot be drawn.
[Response] The text in the article is that “OAA in the DAC relied most on glacier delayed runoff and meltwater runoff to irrigate and maintain agriculture as well as to maintain soil moisture, vegetation growth, and groundwater replenishment to maintain food security” in lines 579-581. The conclusion that oases are most dependent on glacier runoff was concluded from previous research (Bury et al., 2013; Clouse et al., 2016; Rasul & Molden, 2019). In this part, we compare meltwater runoff and delayed runoff, two components of glacier runoff, with the domestic, industrial, and irrigation consumption water in oases of DAC, in order to show the relative importance of glacier runoff. So hydrological processes are not taken into account in the original text. However, following your comments, we also think that adding a one-year description of the whole hydrological process of glacier runoff to the oases would make our study more convincing. We hope that we can have the opportunity to add an example to illustrate it later.
[Reviewer #1 Specific Comment 22] P33: ‘For example, due to increased temperature and reduced glacier runoff, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds’ -- I think such a statement requires a reference. Moreover, a lack of precipitation and snowmelt and increased evaporation caused a severe drought, rather than the small ‘reduced glacier runoff’ contribution.
[Response] We apologize for missing reference to this sentence “For example, due to increased temperature and reduced glacier runoff, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds”. Based on your comment and the references, we will revise the sentence as follows:
“For example, due to increased temperature and reduced snowmelt or precipitation, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds due to declining runoff, including glacier runoff (Gonzalez et al., 2018; Rasul & Molden, 2019).”
[Reviewer #1 Specific Comment 23] P33: ‘In the future, glacier runoff will reach its peak when glacier tourism disappears’ -- What is the connection between these two processes?
[Response] We apologize for the unclear statement. The sentence should be corrected as follows:
“Under climate change, the reliability of the natural snow on the traditional glaciers has decreased and the ski season has shortened, posing a certain risk to the ski tourism industry (Falk, 2016; Rasul & Molden, 2019). For example, the ski season in Ontario and Quebec was shortened between 2000 and 2010, and the recent record warm winter resulted in a 10-15% drop in visitors (Scott et al., 2012a). At the same time, considering the human influence could accelerate the melting of the glaciers, some glacier tourism has been canceled, such as Tien Shan in Xinjiang of China. Appropriate human activities in glacial areas, especially on the surface of glaciers, such as hiking, skiing, etc., will not be the main cause of glacier loss, these activities can be carried out. However, authorities in Xinjiang have stopped glacier tourism in Tien Shan, arguing that the loss of glaciers will be far greater than glacier tourism. In the past decade, glacier tourism revenue in Xinjiang was less than 1 billion yuan, but the loss caused by glacier collapse or melting was incalculable (Liu, 2016). Similarly, at Yulong Snow Mountain, the local government is considering stopping glacier tourism as the glacier is also shrinking at an accelerating rate. So, as glacier runoff increases, glacier tourism in many regions may stop for balance melting purposes.”
[Reviewer #1 Specific Comment 24] P34: The linear regression is only introduced in the conclusion (I could not find it elsewhere in the manuscript). Apart from that, how does the study deal with the non-linear change in glacier runoff (peakwater)?
[Response] The linear regression was introduced in line 441. We used the function FORECAST.LINEAR in Microsoft Excel to predict glacier runoff in the next decade simply as the annual data of glacier runoff obtained are non-stationary series. The results of prediction are compared with the previous 55 years of calculated glacier runoff data to determine whether the glacier is “Increase continuously”, “Decrease continuously” or is “Reach the peak soon”. The changing slope can be calculated using the mean value of each decade. If the slope is larger than 0.005%, it means increasing continuously, while decreasing continuously happens when the slope is smaller than -0.005%. If the slope is in the range of ±0.005%, it is considered to be reaching the peak of glacier runoff soon (except Karakoram). We apologize for missing the description of this part and will add it to the paper.
[Reviewer #1 Specific Comment 25] P34: Nothing that is mentioned at point three in the conclusion I can find in the results section. Where do these conclusions come from?
[Response] The first sentence in the third conclusion “as a continental glacier, the glacier runoff studied in this paper was mainly regulated by hydrothermal regulation, in which temperature was the dominant factor, followed by precipitation” was from lines 575-577 in section 4.3 Impact factors. We apologize for the wrong number in the second sentence “since the water source of the oases in the DAC was mostly glaciers and the total GDP of the OAAs accounted for 76.92% of that of the northwestern DAC, glacier runoff had a greater impact on local agriculture, animal husbandry, and economy” from lines 584-585, the correct proportion is 79.86%. And the third sentence “in the future, it is necessary to quantify the impact of each change in the cryosphere on social production factors more precisely” is a summary statement based on the impact factors of glacier runoff and its socio-economic consequences.
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AC4: 'Supplementary Reply on RC1 (Methods, Glacier Area Change, and Oases)', Xuejing LENG, 22 Nov 2021
Nov 22, 2021
Thanks again for your helpful and valuable comments on our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). After studying your comments carefully, we have made some corrections which we hope to meet with approval.
- First of all, we rewrite the Methods and annotate parameters correctly. As for some details we have discussed too much, such as the reasons for choosing Shean Estimation and APHRODITE, we use charts and figures to illustrate them in supplementary materials. We also add the methods to calculate the glacier area change. The revised Methods with supplementary materials are attached in the supplementary materials.
- We add the analysis of changes in glacier areas. Glacier outlines were extracted from Landsat TM scenes in the two periods (Region1985-1995 and Region1995-2005) in each basin at the end of ablation seasons (September to November), respectively, in Google Earth EngineTM (hereafter, GEE) based on band ratio segmentation method (Guo et al., 2015; Paul et al., 2009; Racoviteau et al., 2009). We also add an analysis of changes in glacier area in Results.
- We think your suggestion "missing a discussion how water from the glaciers reaches the agricultural areas " should be further discussed. While our article focuses on high-resolution glacier runoff calculating on regional scales but not the hydrological distribution model, the accurate value arrived at the oases (how water reached) is not our goal in this paper. As rivers in DAC are nourished to a high degree by glacier meltwater and also the glacier meltwater is the main artery for the oases in the DAC (Kaser et al., 2010, Wang et al., 2013). Changes in glacier runoff could alter the runoff in the whole river basin. However, the contribution of glacier runoff to oases is fuzzy and hard to quantify (Tino et al., 2013). Most studies also show that glacier runoff is crucial to oases, but there is no quantitative study on how it affects oases (Chen et al., 2019; Fang et al., 2018; Ma et al., 2015; Patrick et al., 2015; Su, 2002; Wang et al., 2012; Yang et al., 2015; Zhang et al., 2021). So, we think that the changing proportion of water withdrawals due to glacier runoff under clime change is sufficient to illustrate the threat of glacier runoff to oases.
Hope the revised sections meet your requirements.
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AC1: 'Reply on RC1', Xuejing LENG, 03 Nov 2021
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RC2: 'Comment on hess-2021-377', Anonymous Referee #2, 04 Nov 2021
Review of “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” by Leng et al. (2021)
The manuscript of Leng et al. derives timeseries of glacier runoff for the dryland areas of China for the period 1961 until 2015 using previously published geodetic mass balance estimates and APHRODITE gridded precipitation and temperature products. Their estimates of glacier runoff are used to indicate the amount of glacier meltwater that comes from the imbalance and balance component of glacier runoff (referred to as meltwater runoff and delayed runoff, respectively, in the manuscript) and to analyze trends. Their analyses are done for 22 basins in northwestern China.
While I find the topic of this paper both an interesting and valuable one for HESS and the dryland areas of China in general, this study is disjointed and left me confused as to the methods and validity of the results. The paper is not well organized, with some topics discussed in far too much detail, often without clearly informing the reader as to a particular method or result. Other topics are either not fully explained, or introduced in different parts of the manuscript, with sometimes conflicting descriptions. The writing and language of this paper requires major improvement if it is to be considered for publication, a careful reading is not sufficient to understand the methods and results – the reader is left to guess how many particular methods were conducted. The sloppy nature of this paper causes confusion with frequent occurrences fragmented explanations and changing or vague terminology and units. Like the Reviewer 1, I cannot recommend this manuscript for publication. However, because I see potential value in the work and great value in this topic, I have included more detailed comments below.
Major comments:
1. Many methods are not well explained: I don’t understand how you get precipitation. You use the 0.25° spatial resolution daily precipitation datasets from the Asian Precipitation – Highly Resolved Observational Data Integration Towards Evaluation Of Water Resources (APHRODITE). But then you state that you “Used the Shean estimation to optimize the precipitation gradient per glacier”. Shean provides annual mass balance – not precipitation, and does not use any precipitation data, so how specifically are you using his method or data? Equations 2, 3 and 4 only use elevation data and APHRODITE precip and temperature data.. not glacier mass balance data.
a. In the next line you state that you are using a precipitation gradient to correct the original APHRODITE data. You then use this gradient “PG” in equations but then never state how you get the gradients until L253-254: “PG in this paper was obtained by interpolation using the mass balance algorithm and geostatistics method”. This is an important point and should be introduced together and fully described, currently this line doesn’t tell us how you get the PG. (Also, is PG a widely used abbreviation for precipitation gradient? I haven’t seen this used).
b. L214, “The precipitation was corrected by the Shean estimation for high-altitude precipitation gradients…”, again, what is this correction, I can’t find any precipitation gradient work in Shean et al. (2020). You have annual mass balance from Shean et al. (2020), precipitation data from APHRODITE, and then estimate ablation with a PDD model. How you use these three datasets in conjunction is not clear.2. L153-156 The PDD values must be stated, what is the range of values? Perhaps show a map of them as a supplemental figure. Further, the uncertainty around these values should be quantified.
3. The terms monthly delayed runoff and meltwater runoff are poorly defined. Is monthly delayed runoff a mix of seasonal snow melt runoff and rainfall over the glacier? In lines 184-186 is Ta meant to be T1? In lines 290-292 you better clarify the terms, which should not be occurring in the results, and still leave the reader confused: “Glacier runoff included delayed runoff that was stored rainfall in the cold seasons and released rainfall in the ablation seasons, while meltwater runoff was caused by glacier mass balance, which was also called excessive meltwater runoff or the imbalanced part of glacial runoff”. Do you mean stored snowpack in the cold season? Or both stored seasonal snowpack and stored rainfall in the cold season? Released rainfall in the ablation seasons?
4. Many other terms are undefined, e.g.: L347 What is “glacier runoff recharge”?
5. Some references are inappropriate.
a. E.g. in your submission you do not cite the information stated in L597-598 about California, then in your response to Reviewer 1 you state: “For example, due to increased temperature and reduced snowmelt or precipitation, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds due to declining runoff, including glacier runoff (Gonzalez et al., 2018; Rasul & Molden, 2019).” --- Rasul and Molden (2019) merely reference the Gonzalez work, and do not offer any data on this so is not suitable to be referenced here. The Gonzalez work can be found here: https://nca2018.globalchange.gov/downloads/NCA4_Ch25_Southwest_Full.pdf, and does not ever mention glaciers.
b. An additional example is in L341 Barnett et al. (2005) is a review paper and did not “simulate glacial runoff” as you claim.6. Using RGI glacier outlines for 1961-2018 is not appropriate for a 100m resolution study. At least an error analysis on the effect of not incorporating glacier area change should be added.
a. In response to Reviewer 1 you state that the RGI polygons were “All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time.” This is close to the case, but as pointed out by Shean et al. (2020)
b. source image timestamps used for RGI polygon digitization (~1998–2014) and the DEM timestamps. This means that the polygons were digitize ANY time between those dates, and contain information about the date.
c. So using a single polygon of 1998-2014 origin is either not appropriate, or requires an uncertainty analysis (which should be included regardless).
d. Also, as detailed by Guo et al. (2017) the first Chinese Glacier inventory was finished in 2002 and covered CGI-1 was compiled based on topographic maps and aerial photographs acquired during the 1950s–80s – so would be a potentially suitable starting outline for you study, then updating to the CGI-2 dating to 2006-2010, compiled by Guo et al. (2017): https://www.cambridge.org/core/journals/journal-of-glaciology/article/second-chinese-glacier-inventory-data-methods-and-results/386DAB512F4869D3335E2DE24B0F43EBSpecific comments:
Any use of numbers should spell out the number if below 10, e.g. 7 regions --> seven regions.
Please use significant digits e.g. L107-108
L15 Is this total annual glacier runoff? Specify time in the sentence or units.
L29 Add “Glaciers and ice sheets are the….”
L35 This is not a feedback, it is a one-way relationship, glaciers melt, producing runoff, increasing sea level. These citations do not fit your point.
L51-57 The problem is not clearly stated here. You state that “Continuous yearly mass balance data for long time series could not be calculated effectively due to the time consumption and high energy consumption of field observations (Brun et al., 2017; Shean et al., 2020).” This is poorly worded and incorrect. Long time series cannot be calculated because the data don’t exist, which in turn is because field observations are logistically and financially difficult.
L62 Two problems here, one, this is an incomplete sentence, and further, why is the resolution so low? Perhaps because the data are not sufficient to use at finer resolutions? “…while the energy balance model could be applied in 62 large regions but with low resolution (such as 0.25 degrees (Sakai et al., 2015))”.
L99 erased the range?
L102 7 glaciers? Or 7 glacier regions?
Figure 1 Font is too small in axes and legend (commonly in many figures)L122-123 Doesn’t make sense. You are implying that you did the work of Shean et al. (2020).
L126-148 Way too long of a description of these studies, if you want to show the comparison in lines 136-145, use a table, this is hard to read.
L267 Blocks represent modules (add the s)
L289-290 “and we overcame the difficulty of large-scale geodetic mass balance assessment” What? Brun et al. (2017) and Shean et al. (2020) did this.
L300-301 “The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin”, wouldn’t the opposite be true? Delayed runoff is not directly from glacier wastage (stored seasonal precip), so is more sustainable than ice wastage.
Figure 3 Units on runoff?? The legend just says “5.6”. How useful are raw runoff numbers versus percent contributions of total river discharge?
L323-338 Replace most this paragraph with a table and reference that table with a few lines.
L324 Glaciers should be lowercase.
Citation: https://doi.org/10.5194/hess-2021-377-RC2 -
AC2: 'Reply on RC2', Xuejing LENG, 14 Nov 2021
Nov 14, 2021
Thank you very much for your helpful and valuable comments on our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). After studying your comments carefully, we have made some corrections which we hope to meet with approval. First of all, we realize that there were many unclear expressions and wrong marks of parameters in the manuscript which confused you. Following your comments, we have modified the corresponding sentence in responding to each specific comment. We will ask a well-established expert to polish our paper in the revised manuscript. According to your all comments, we think the main corrections in the paper are as follows:
1. Rewrite the Methods. We annotate parameters correctly, explain the meanings of parameters clearly, and supplement the calculations of ablation and positive-degree days. As for some details we have discussed too much, such as the reasons for choosing Shean Estimation and APHRODITE, we use charts and figures to illustrate them in supplementary materials.
2. Check references to make sure they are referred to correctly. Adjust texts, legends, and parameters in each figure make them accurate and easy to read.
3. Add the uncertainty analysis of glacier area change. We decided to use Landsat TM/ETIM+ scenes on GEE to obtain the changes of glacier area during each period of dryland areas of China from 1985 to 1995 and 1995 to 2005. Following your comment, glacier areas during 2005-2015 were represented by the second Chinese Glacier Inventory (CGI-2). We compare glacier areas from remote sensing imageries with RGI in each period to analyze uncertainties brought by glacier area change. If some input scenes are masked after the cloud algorithm, we use RGI instead in these regions. The codes for calculating glacier areas are attached at the end of the response.
4. For the socio-economic results of glacier runoff, a specific analysis of the impacts of glacier runoff on oases (e.g. using hydrological models) can be supplemented to increase the persuasiveness of this paper.
A detailed point-by-point response to your comment and suggestion is as follows:
[Reviewer #2 Major Comment 1] Many methods are not well explained: I don’t understand how you get precipitation. You use the 0.25° spatial resolution daily precipitation datasets from the Asian Precipitation – Highly Resolved Observational Data Integration Towards Evaluation Of Water Resources (APHRODITE). But then you state that you “Used the Shean estimation to optimize the precipitation gradient per glacier”. Shean provides annual mass balance – not precipitation, and does not use any precipitation data, so how specifically are you using his method or data? Equations 2, 3, and 4 only use elevation data and APHRODITE precip and temperature data.. not glacier mass balance data.
[Response] We are sorry for our disordered structure in Methods which confused you so much. Since there were some mistakes in Equations 3 and 4 and omitting an Equation about calculating ablation on a glacier, correct and complete Equations on reconciling high-altitude precipitation are as follows:
“By=Ab,y+Ac,y=∫(Ab+Ac)dt (1)
Ab,y=DDF×PDDy (2)
Ac,d={(Pcor,d,Ta≤0@(1-Ta/T1 ) Pcor,d,0<Ta≤4@0,Ta>4)} (3)
∆H=H-Hrmd (4)
Pcor,d=Prmd,d∙{1+[∆H+(H-Hmap)]∙PG∙0.01} (5)”
Eq.1 shows the mass balance (By) is the sum of accumulation (Ac,y) and ablation (Ab,y) at a yearly time step of each glacier. Eq.2 shows the yearly ablation is the product of the degree-day factor (DDF) and positive-degree days (PDDy) of each glacier obtained in the daily temperature dataset. While precipitation is separated into solid and liquid by temperature, only solid precipitation, snow, count as atmospheric mass accumulation. Eq.3 indicates the calculation about daily accumulation by corrected high-altitude temperature (Ta), which decreases 0.65 degrees per 100 m rise corrected by DEM data. Eq.4 and Eq.5 show the reconciled high-altitude precipitation (Pcor,d) was calculated as a function of original precipitation data from APHRODITE (Prmd,d), the vertical precipitation gradient (PG), the mean terrain elevation from DEM (H), the aggregated elevation at a spatial resolution with 0.25 degrees consistent with APHRODITE (Hrmd), and maximum rainfall height (Hmap) at a daily time step for each glacier.1. We use the Shean Estimation of the mass balance and their uncertainties as annual mass balance (B_y) while Shean Estimation showed the average mass balance from 2000 to 2018 for each glacier.
2. Using the product of the distribution map of DDF and PDDy to obtain the yearly ablation (Ab,y) at a grid scale with a spatial resolution of 100 m. For each glacier, yearly ablation (Ab,y) was calculated on values within the zones of RGI shapefiles.
3. The annual accumulation (Ac,y) on each glacier was calculated based on 1 and 2.
4. The annual accumulation (Ac,y) of each glacier calculated in 3 was substituted into Eq. 3-5, the vertical precipitation gradient (PG) of each glacier was obtained by combining elevation data, corrected high-altitude temperature data (Ta), and the maximum rainfall height (Hmap) of each glacier region.
5. As the spatial resolution of the temperature and precipitation dataset from APHRODITE is 0.25°, which is quite different from the area of glaciers, the vertical precipitation gradient between nearby glaciers may be quite different. We interpolated each glacier’s precipitation gradient to smooth the errors caused by the boundary of the raster data.
In Step 5, the map of interpolated vertical precipitation gradient (PG) was obtained. Using original temperature and precipitation (Prmd,d) from APHRODITE according to Eq.3-5 to calculate corrected high-altitude precipitation (P_(cor,d)) and accumulation (A_(c,d)) at a daily step on a grid cell. The daily ablation (Ab,d) on a grid cell could be calculated by Eq. 2, and then the daily mass balance (Bd) on a grid cell could be obtained according to Eq. 1. The grid cell is unified at a spatial resolution with 100 m in this step.
The above six steps are the complete process of the raster dataset of regional glacier mass balance obtained after high-altitude precipitation correction by Shean Estimation in this paper.
[Reviewer #2 Major Comment 1. a] In the next line you state that you are using a precipitation gradient to correct the original APHRODITE data. You then use this gradient “PG” in equations but then never state how you get the gradients until L253-254: “PG in this paper was obtained by interpolation using the mass balance algorithm and geostatistics method”. This is an important point and should be introduced together and fully described, currently this line doesn’t tell us how you get the PG. (Also, is PG a widely used abbreviation for precipitation gradient? I haven’t seen this used).
[Response] We are sorry again for the unclear narrative structure in Methods. Vertical precipitation gradients (PG) were calculated after obtaining accumulation (Ac) (corrected high-altitude precipitation relevant to high-altitude temperature, Pcor) by subtracting mass balance (By) from Shean Estimation to ablation (A_b) for each glacier. The PG is just an abbreviation for precipitation gradients and a parameter in equations in this paper but not a widely used abbreviation. We got a map of interpolated precipitation gradients (PG) to smooth the errors caused by the boundary of the raster data at a spatial resolution of 0.25 degrees. Then, using original temperature and precipitation (Prmd,d) from APHRODITE to calculate corrected high-altitude precipitation (Pcor,d) and accumulation (Ac,d) at a daily step on a grid cell. Daily ablation (Ab,d) on a grid cell could be calculated by Eq.2 and we obtained map of daily mass balance for glacier regions at a spatial resolution of 100 m.[Reviewer #2 Major Comment 1. b] L214, “The precipitation was corrected by the Shean estimation for high-altitude precipitation gradients…”, again, what is this correction, I can’t find any precipitation gradient work in Shean et al. (2020). You have annual mass balance from Shean et al. (2020), precipitation data from APHRODITE, and then estimate ablation with a PDD model. How you use these three datasets in conjunction is not clear.
[Response] Thanks for your comment and we apologize for the unclear paragraphs in Methods. We will rewrite the method section to avoid confusion and make it clearer. As mentioned in the previous responses, mass balance with uncertainties for each glacier from Shean Estimation provided annual mass balance (By). Positive-degree days (PDD) are accumulated by daily temperature from APHRODITE corrected by DEM (0.65℃/100 m). Ablation (Ab,y) is calculated by the product of PDD and map of DDF provided by Zhang et al. After subtracting mass balance to ablation, annual accumulation (Ac,y) from 2000-2018 (Shean et al., 2020) for each glacier could be obtained. According to Eq.3-5, the precipitation gradient for each glacier could be calculated with the help of original precipitation (Prmd,d) from APHRODITE. Substituting the map of interpolated precipitation gradient and precipitation from APHRODITE into Eq.1-5, yearly maps of mass balance for glaciers in dryland areas of China could be obtained.[Reviewer #2 Major Comment 2] L153-156 The PDD values must be stated, what is the range of values? Perhaps show a map of them as a supplemental figure. Further, the uncertainty around these values should be quantified.
[Response] Thanks for your suggestion and following your comment, we add a description of positive-degree days as follows:
“Monthly positive-degree days (PDDm) were chosen instead of absolute PDD (Braithwaite & Olesen, 1993) which were summed positive daily average temperatures. However, as we used temperature from APHRODITE, uncertainties around temperature and PDDm could not be quantified. We could add a map of PDDm as a supplemental figure.[Reviewer #2 Major Comment 3 a] The terms monthly delayed runoff and meltwater runoff are poorly defined. Is monthly delayed runoff a mix of seasonal snowmelt runoff and rainfall over the glacier?
[Response] We are sorry for missing detailed and accurate definitions of delayed runoff and meltwater runoff. Delayed runoff is defined in lines 178-181 as “Based on the definition of glacier runoff, the runoff includes two parts. One is the precipitation on glaciers stored in the non-melting season and released in the melting season, which is called delayed runoff (Kaser et al., 2010; Pritchard, 2019; Shean et al., 2020)”. Actually, glacier runoff in this paper refers to the runoff generated in glacier regions. According to Eq.1, mass balance (By) is the sum of accumulation (Ac,y) and ablation (Ab,y) at a yearly time step of each glacier. While mass balance is a positive value, it means there is accumulation caused by precipitation on the glacier, and the amount greater than 0 forms runoff according to the PDD of each month. So, delayed runoff refers to the amount of precipitation accumulated at high altitudes after offsetting by the ablation and stored in the mountains as snow in the cold seasons and discharged in the warm seasons, not including meltwater runoff.[Reviewer #2 Major Comment 3 b] In lines 184-186 is Ta meant to be T1?
[Response] We are sorry for these mistakes. In lines 184-186, what T_a meant to say is T_1, which is 4 ℃ in this paper. We will replace T_1 in the original text with 4 ℃ used in the actual calculation to avoid confusion.[Reviewer #2 Major Comment 3 c] In lines 290-292 you better clarify the terms, which should not be occurring in the results, and still leave the reader confused: “Glacier runoff included delayed runoff that was stored rainfall in the cold seasons and released rainfall in the ablation seasons, while meltwater runoff was caused by glacier mass balance, which was also called excessive meltwater runoff or the imbalanced part of glacial runoff”. Do you mean stored snowpack in the cold season? Or both stored seasonal snowpack and stored rainfall in the cold season? Released rainfall in the ablation seasons?
[Response] We apologize for the unclear sentence. We divided glacier runoff into two parts in this paper while one is delayed runoff, the other is meltwater runoff. As mentioned in the former response, delayed runoff refers to the amount of precipitation accumulated at high altitudes after offsetting by the ablation and stored in the mountains as snow in the cold seasons and discharged in the warm seasons, not including meltwater runoff. Meltwater runoff, which is also called excessive meltwater runoff or the imbalanced part of glacier runoff, is caused by glacier mass balance. While mass balance is a negative value, glaciers recede during warm seasons. Delayed runoff emphasizes the release of precipitation offsetting ablation stored in cold seasons on glaciers during warm seasons, while meltwater runoff emphasizes the amount of melting of the glacier itself due to its mass balance during warm seasons. The corrected sentence reads as:
“To be precise, glacier runoff in this study is runoff generated in glacier regions, including meltwater runoff and delayed runoff. Delayed runoff was caused by remaining precipitation stored in cold seasons and discharged in warm seasons after offsetting ablation. Meltwater runoff, which was also called excessive meltwater runoff or the imbalanced part of glacier runoff, was caused by mass loss of glaciers when atmospheric accumulation cannot offset ablation on glaciers.”[Reviewer #2 Major Comment 4] Many other terms are undefined, e.g.: L347 What is “glacier runoff recharge”?
[Response] We apologize for the undefined term “glacier runoff recharge” in lines 347-348 “The percentage of glacier runoff recharge calculated by the DDF model was between 5% and 15% based on the first Chinese inventory and monthly precipitation and temperature data from the National Meteorological Centre (Gao et al., 2010)”. Glacier runoff recharge here refers to glacier runoff as a percentage of surface runoff recorded by hydrological stations. The corrected sentence reads as:
“The percentage of glacier runoff calculated by the DDF model was between 5% and 15% based on the first Chinese inventory and monthly hydrothermal data from the National Meteorological Centre (Gao et al., 2010).”
[Reviewer #2 Major Comment 5 a] Some references are inappropriate. E.g. in your submission you do not cite the information stated in L597-598 about California, then in your response to Reviewer 1 you state: “For example, due to increased temperature and reduced snowmelt or precipitation, California, in the United States, experienced a severe drought from 2011 to 2015 where hydroelectric power decreased by two-thirds due to declining runoff, including glacier runoff (Gonzalez et al., 2018; Rasul & Molden, 2019).” --- Rasul and Molden (2019) merely reference the Gonzalez work, and do not offer any data on this so is not suitable to be referenced here. The Gonzalez work can be found here: https://nca2018.globalchange.gov/downloads/NCA4_Ch25_Southwest_Full.pdf, and does not ever mention glaciers.
[Response] In the response to Reviewer #1, we only added references neglecting to check the contents of them. Following your comments, we recognize no matter Gonzalez et al. (2018) or Rasul & Molden (2019) are inappropriate referred here. Thanks again for providing the Gonzalez work and your valuable comments. Here we would like to state the impact of glacier shrinkage on hydropower as follows:
“Some countries where the main source of electricity is hydropower, glacier runoff contributed significantly to its origination such as France (Milner et al., 2017) and Norway (Andreassen et al., 2005). 19 hydropower plants in the glacier-fed Rhone River supplied 25% of French hydropower and 15% of hydropower used runoff comes from glacierized basins in Norway.”[Reviewer #2 Major Comment 5 b] Some references are inappropriate. An additional example is in L341 Barnett et al. (2005) is a review paper and did not “simulate glacial runoff” as you claim.
[Response] We apologize for the misquotation of Barnett et al. (2005) which is a review paper not mentioning glacier runoff simulation. Even the contents in Section “Impacts on regional water supplies” were about Himalaya-Hindu Kush region not dryland areas of China. So we delete this reference here and add a new one. The corrected complete sentence with references reads as:
“Some studies (Hussain et al., 2019; Li et al., 2018; Shen et al., 2004; Wang et al., 2015; Wu et al., 2018; Yang et al., 2015; Ye et al., 2017) simulated glacial runoff in the DAC by qualitative or semi-quantitative methods or by using models.”[Reviewer #2 Major Comment 6] Using RGI glacier outlines for 1961-2018 is not appropriate for a 100m resolution study. At least an error analysis on the effect of not incorporating glacier area change should be added.
a. In response to Reviewer 1 you state that the RGI polygons were “All glacier extents were obtained started in the 1990s and finished in 2014 which is consistent with our research time.” This is close to the case, but as pointed out by Shean et al. (2020)
b. source image timestamps used for RGI polygon digitization (~1998–2014) and the DEM timestamps. This means that the polygons were digitize ANY time between those dates, and contain information about the date.
c. So using a single polygon of 1998-2014 origin is either not appropriate, or requires an uncertainty analysis (which should be included regardless).
d. Also, as detailed by Guo et al. (2017) the first Chinese Glacier inventory was finished in 2002 and covered CGI-1 was compiled based on topographic maps and aerial photographs acquired during the 1950s–80s – so would be a potentially suitable starting outline for you study, then updating to the CGI-2 dating to 2006-2010, compiled by Guo et al. (2017): https://www.cambridge.org/core/journals/journal-of-glaciology/article/second-chinese-glacier-inventory-data-methods-and-results/386DAB512F4869D3335E2DE24B0F43EB
[Response] We note that both you and Reviewer #1 have put forward opinions on the change of glacier areas. In our response to reviewer 1, we explained that we thought uncertainties brought by areas were smaller than uncertainties brought by glacier mass balance (Shean Estimation) so changes in areas of glaciers were not taken into account in this article. However, following your and Reviewer #1’s comments, we will add error analysis on the effect of neglecting areas change.
Thank you very much for providing the article about the second Chinese Glacier Inventory (CGI-2). We learned the CGI-2 was compiled based on 218 remote sensing imageries during 2006-2010 end of ablation seasons using band ratio segmentation method and corrected by field GPS investigation and outlines delineated from high-resolution Google MapsTM images. The CGI-2 (Guo et al., 2015) was the most accurate glacier inventory in China since the 21st century. Based on it, we think about some strategies for analyzing uncertainties about area change of glaciers. Glacier outlines can be obtained from Landsat TM/ETM+ scenes in the two periods (Region1985-1995 and Region1995-2005) in each basin, respectively, in Google Earth EngineTM (hereafter, GEE) based on band ratio segmentation method same as Guo et al. (2015) If scenes are limited by cloud cover or lack of data, we use RGI instead. Kappa coefficient is used to calculate the accuracy of comparison between Region1985-2005 and Google Earth MapTM for each similar scene time. Uncertainties due to area change during 1961-2015 in different basins brought by RGI can be calculated as following equations:
ERGI,i=(ARGI,i-AGEE,i∙Ki)/ARGI,i ×100%
Where ERGI,i is the glacier area error, ARGI,i is the glacier area provided by RGI, AGEE,i is the glacier area calculated by GEE, Ki is the Kappa coefficient between glacier areas calculated by GEE and outlines from Google Earth MapTM, i indicates different basins. And the total glacier area error can be calculated using:
ERGI=√(∑_(i=1)^n▒〖(ERGI,i)〗^2 )
The code of extracting glacier outline in GEE is attached in the supplementary materials. Hope this strategy can solve the problem of uncertainties analysis caused by area change and thanks again for providing references and suggestions.[Reviewer #2 Specific Comment 1] Any use of numbers should spell out the number if below 10, e.g. 7 regions --> seven regions.
[Response] Thanks for your comments and we will exchange the use of numbers below 10 in the whole paper. The corrected sentences read as:
“two goals in the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) (Line 27)
The seven glaciers affect 22 tertiary watersheds in the DAC, including six drainage basins which all originated directly from glaciers and across arid and hyper-arid regions (hereafter, AH). Two river basins were both completely in the arid zone while 11 drainage basins were in both semiarid and arid regions (hereafter, SA). (Lines 102-105)
Based on the RGI 6.0, six glacier regions influence the DAC. (Line 136)”[Reviewer #2 Specific Comment 2] Please use significant digits e.g. L107-108
[Response] We apologize for the unprecise expression. Following your comment, the corrected sentence reads as:
“As Table 1 shows, the area of OAAs in each watershed in the DAC reached a maximum of 21699.18 km2 (Middle Rivers Basin), with an average of 6543.69 km2, while the precipitation in the DAC reached a maximum of 323.09 mm (Qinghai Lake Drainage System), with an average of 134.56 mm, which revealed that runoff in the DAC was extremely important, especially in some basins where runoff originated almost entirely from glaciers.”[Reviewer #2 Specific Comment 3] L15 Is this total annual glacier runoff? Specify time in the sentence or units.
[Response] We are sorry for the unclear sentence. Following your comment, the corrected sentence reads as:
“The total annual glacier runoff in the DAC is (98.52 ± 67.37) × 108 m3 during 1961-2015, in which the meltwater runoff is (63.43 ± 42.17) × 108 m3, accounting for 64.38%.”[Reviewer #2 Specific Comment 4] L29 Add “Glaciers and ice sheets are the….”
[Response] Thanks for your comments. The corrected sentence reads as:
“Glaciers and ice sheets are the largest reservoirs of fresh water on Earth, and they store most of the ice and snow (Beniston & Stoffel, 2014; Kraaijenbrink et al., 2017).”[Reviewer #2 Specific Comment 5] L35 This is not a feedback, it is a one-way relationship, glaciers melt, producing runoff, increasing sea level. These citations do not fit your point.
[Response] Thanks for your comments. As mentioned in response to Reviewer #1’s specific comment 1, what we want to point here is that warming expedites glaciers to melt and then speeds up raising sea levels under current climatic conditions. The increase in meltwater can alleviate drought in the river basins originated from glaciers like the drylands of China, but sea level rise poses risks to coastal areas, meaning that the meltwater of glaciers is not only a result of climate change but also contributing to the consequences of climate change such as rising sea levels. So, we think we could change the sentence and references as follows:
“Under current climatic conditions, warming expedites glaciers to melt and meltwater speeds raising sea levels, which is why glaciers are both the result of and contributor to climate change.”[Reviewer #2 Specific Comment 6] L51-57 The problem is not clearly stated here. You state that “Continuous yearly mass balance data for long time series could not be calculated effectively due to the time consumption and high energy consumption of field observations (Brun et al., 2017; Shean et al., 2020).” This is poorly worded and incorrect. Long time series cannot be calculated because the data don’t exist, which in turn is because field observations are logistically and financially difficult.
[Response] We are sorry for the unclear statement. We intended to express that the financial and logistic difficulties of field observations result in the lack of long-time series in regional scales. Thank you very much for your comment so we will amend this sentence to read as:
“Continuous yearly mass balance data for long time series in regional scales could not be calculated effectively due to the financial and logistic difficulties of field observations (Brun et al., 2017; Shean et al., 2020).”[Reviewer #2 Specific Comment 7] L62 Two problems here, one, this is an incomplete sentence, and further, why is the resolution so low? Perhaps because the data are not sufficient to use at finer resolutions? “…while the energy balance model could be applied in 62 large regions but with low resolution (such as 0.25 degrees (Sakai et al., 2015))”.
[Response] We are sorry for the incomplete sentence. In this sentence, we wanted to express two messages. First, we wanted to indicate that the relationship between the recorded data of meteorological stations based on the degree-day factor model and glacier runoff cannot be applied in regional scales limited by the distribution of meteorological stations (Duan et al., 2017). Second, although Sakai et al. established the map of ELA in regional scales, the resolution was low with 0.5 degrees, which could not be applied in scales of basins proposed in this paper. Sakai et al. derived Asian glaciers from the Glacier Area Mapping for Discharge in Asian Mountains (GAMDAM) glacier inventory (GGI) (Nuimura et al., 2015) to evaluate the clime regime at high-mountain Asia. While the GGI occupied the grids of glacier regions as 0.25 degrees and datasets used such as ERA-Interim reanalysis data – including temperature (level), surface wind (surface flux 10m), surface humidity (surface), and solar radiation (surface flux) - from 1952 to 2007, and APHRODITE from 1952 to 2007 was at a spatial resolution of 0.75 degrees and 0.50 degrees, respectively, so Sakai’s paper was with a resolution of 0.50 degrees. Following your comment, the modified sentence and references read as:
“However, limitations were obvious. Establishing the relationship between stations and the degree-day factor model was too difficult in large regional scales limited by numbers and the distribution of meteorological stations (Duan et al., 2017). Also, the energy balance model could be applied in large regions but limited by resolution for multiple datasets (Sakai et al., 2015).”[Reviewer #2 Specific Comment 8] L99 erased the range?
[Response] While using the aridity index to zone arid regions, the Qinghai-Tibet Plateau will be included in arid areas. Due to the specificity of the Qinghai-Tibet Plateau, our team thinks the area should be studied separately. Therefore, the arid zone used in this paper excludes the Qinghai-Tibet Plateau. Following your comment, the corrected sentence reads as:
“The region of DAC was obtained relying on aridity index supported by the United Environment Programme (UNEP) excluding the range of the Tibetan Plateau which should be discussed separately because of its particularity.”[Reviewer #2 Specific Comment 9] L102 7 glaciers? Or 7 glacier regions?
[Response] We are sorry for the wrong expression. The modified sentence reads as:
“The seven glacier regions affect 22 tertiary watersheds in the DAC, including six drainage basins which all originated directly from glaciers and across arid and hyper-arid regions (hereafter, AH).”[Reviewer #2 Specific Comment 10] Figure 1 Font is too small in axes and legend (commonly in many figures)
[Response] Following your comment, we make fonts in each figure larger to make it easier for readers.[Reviewer #2 Specific Comment 11] L122-123 Doesn’t make sense. You are implying that you did the work of Shean et al. (2020).
[Response] Thanks for your comment. This sentence is meant to introduce how Shean et al. (2020) obtained the mass balance dataset. Following your comment, the modified sentence reads as:
“We used regional available glacier mass balance dataset to correct high-altitude precipitation.”[Reviewer #2 Specific Comment 12] L126-148 Way too long of a description of these studies, if you want to show the comparison in lines 136-145, use a table, this is hard to read.
[Response] Thanks for your comment, we are going to illustrate this comparison using a table attached in supplementary materials. The table is attached at the end of this response.[Reviewer #2 Specific Comment 13] L267 Blocks represent modules (add the s)
[Response] Thanks for your careful reading. The corrected sentence reads as:
“Fig. 2. Conceptual framework of glacier runoff calculating. Blocks represent modules of 267 the glacier runoff calculation in each category. Shading indicated results with uncertainties and different lines and blocks indicated the corresponding modules.”[Reviewer #2 Specific Comment 14] L289-290 “and we overcame the difficulty of large-scale geodetic mass balance assessment” What? Brun et al. (2017) and Shean et al. (2020) did this.
[Response] We are sorry for the wrong expression. The corrected sentence reads as:
“In this paper, Shean Estimation was used to reconcile high-altitude precipitation. The yearly mass balance of glaciers influencing the DAC from 1961 to 2015 was calculated by the difference between accumulation obtained from corrected precipitation and ablation calculated by the DDF model. A long-time series dataset of total glacier runoff dataset including delayed runoff and meltwater runoff based on temperature was created, which was at large regional scales with a spatial resolution of 100 m. It is important to note that glacier runoff in this paper means runoff generated within the geographical area of a glacier”[Reviewer #2 Specific Comment 15] L300-301 “The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components coming from delayed runoff; therefore, more attention should be paid to glacier disasters in this basin”, wouldn’t the opposite be true? Delayed runoff is not directly from glacier wastage (stored seasonal precip), so is more sustainable than ice wastage.
[Response] As mentioned in Response to Reviewer #1’s specific comment 17, Kriya Rivers Basin is special where 93.67% of glacier runoff comes from delayed runoff. It could be said that delayed runoff is basically determined by rainfall and temperature, which is distinguished from meltwater runoff. Therefore, when extreme precipitation climate occurs, it is easy to cause geologic hazards such as flash floods which should be paid attention to (Kaltenborn et al., 2010; Shen et al., 2004). The hazards here are more related to extreme rainfall than with the glaciers themselves. But referring to your and Reviewer #1’s comment and some references, we think Kashgar River basin, Hotan River basin, and Yarkand River basin should be paid more attention to because delayed runoff and meltwater runoff account for a certain proportion in each basin. The combination of extreme precipitation and rapid snow melting would increase runoff in glacier areas and make them more prone to disasters. The corrected sentence reads as:
“The creeks of the Kriya Rivers basin were the most unique, with 93.67% of the components coming from delayed runoff. More attention should be paid to Kashgar River basin, Hotan River basin, and Yarkand River basin where delayed runoff and meltwater runoff account for a certain proportion and annual total glacier runoff was large. While extreme precipitation happened with rapid snow melting, glacier runoff would increase in haste to make these basins more prone to disasters (Kaltenborn et al., 2010; Shen et al., 2004).”[Reviewer #2 Specific Comment 16] Figure 3 Units on runoff?? The legend just says “5.6”. How useful are raw runoff numbers versus percent contributions of total river discharge?
[Response] We are sorry for the unclear legend in Figure 3. The “5.6” represents that the longest column in the legend was 5.6×108 m3. We will correct our figures to make them more clearly. The percentage of glacier runoff relative to total river discharge is helpful to distinguish water sources and provide some references for water allocation after glacier shrinkage under climate change in the future.[Reviewer #2 Specific Comment 17] L323-338 Replace most this paragraph with a table and reference that table with a few lines.
[Response] Thanks for your comment and we simplify the description with tables to make it easier for readers to understand.
[Reviewer #2 Specific Comment 18] L324 Glaciers should be lowercase.
[Response] Thanks for your comment. The corrected sentence reads as:
“From 1961 to 2015, glaciers in the arid regions provided (63.43 ± 42.17) × 108 m3 of glacial excess meltwater.”References:
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AC3: 'Supplementary Reply on RC2 (Methods and Glacier Area Change)', Xuejing LENG, 22 Nov 2021
Thanks again for your helpful and valuable comments on our manuscript entitled “The Spatiotemporal Regime of Glacier Runoff in Oases Indicates the Potential Climatic Risk in Dryland Areas of China” (ID: HESS-2021-377). After studying your comments carefully, we have made some corrections which we hope to meet with approval.
- First of all, we rewrite the Methods and annotate parameters correctly. As for some details we have discussed too much, such as the reasons for choosing Shean Estimation and APHRODITE, we use charts and figures to illustrate them in supplementary materials. We also add the methods to calculate the glacier area change. The revised Methods with supplementary materials are attached in the supplement.
- We add the analysis of changes in glacier areas. Glacier outlines were extracted from Landsat TM scenes in the two periods (Region1985-1995 and Region1995-2005) in each basin at the end of ablation seasons (September to November), respectively, in Google Earth EngineTM (hereafter, GEE) based on band ratio segmentation method (Guo et al., 2015; Paul et al., 2009; Racoviteau et al., 2009). The distribution of different sizes in different basins is shown in the supplements. We also add an analysis of changes in glacier area in Results.
Hope the revised version meets your requirements.
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AC2: 'Reply on RC2', Xuejing LENG, 14 Nov 2021
Data sets
Glacier runoff in dryland areas of China Xuejing Leng, Xiaoming Feng, Bojie Fu and Yu Zhang https://doi.org/10.17605/OSF.IO/C8PHR
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2 citations as recorded by crossref.
- Hydroclimatic variations in the Tianshan Mountains based on grain size and geochemistry of core sediments since ∼1490 CE B. Lan et al. 10.1007/s11629-022-7818-3
- Regional Characteristics and Impact Factors of Change in Terrestrial Water Storage in Northwestern China From 2002 to 2020 J. Yin et al. 10.1109/JSTARS.2022.3224864