the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
The impact of future climate projections and anthropogenic activities on basin-scale groundwater availability
Abstract. Groundwater is under the pressure of changing climate and increasing anthropogenic demand. In this study, we project the effect of these two processes on the projected future groundwater status. Climate projections of Representative Concentration Pathway (RCP) 4.5 and RCP8.5 from the Coupled Model Intercomparison Project Phase 6 (CMIP6) drive a one-way coupled fully distributed hydrological and groundwater model. In addition, three plausible groundwater abstraction scenarios with diverging predictions from increasing, constant, to decreasing volumes and spatial distribution are used. Groundwater status projections are assessed for the short-term (2030), mid-term (2050), and long-term (2100) periods. We use the Bandung groundwater basin as our study case, located 120 km from the current capital city of Indonesia, Jakarta, which is currently under a relocation plan. It is selected as the future anthropogenic uncertainties in the basin, related to the projected groundwater abstraction, is in agreement with our developed scenarios. Results show that changes in the projected climate input, including intensifying rainfall and rising temperature, do not propagate notable changes in groundwater recharge. Under the current unsustainable groundwater abstraction rate, the confined piezometric heads are projected to drop up to a maximum of 7.14 m, 15.25 m, and 29.51 m in 2030, 2050, and 2100, respectively. When groundwater abstraction expands in proportion to the present population growth, the impact is worsened almost two-fold. In contrast, if the groundwater abstraction decreases because of the relocated capital city, the groundwater storage starts to show replenishment potential. As a whole, projected groundwater status changes are dominated by anthropogenic activity, and less so by changes in climatic forcing. The results of this study are expected to demonstrate and inform responsible parties in operational water management on the issue of the impact of projected climate forcing and anthropogenic activity on future groundwater status.
- Preprint
(23177 KB) - Metadata XML
- BibTeX
- EndNote
Status: closed
-
RC1: 'Comment on hess-2024-26', Anonymous Referee #1, 02 Apr 2024
The paper quantifies the impact of future climate change and changes in groundwater pumping on groundwater resources in the Bandung groundwater basin, Indonesia. This is done by driving a surface water and groundwater model with CMIP6 climate projections and various groundwater abstraction scenarios. Results show that groundwater abstraction has a larger impact on groundwater levels/storage than climate-induced changes in groundwater recharge.
The paper tackles an important and relevant topic and is generally well written. The following comments identify several points that deserve attention.
-Based on the introduction, novelty of the paper seems to be largely limited to the case study, since the literature review shows that very similar methodology has been used before with similar conclusions (groundwater abstractions more important than climate change). To justify publication in HESS the authors should strengthen the novelty description of their work in the introduction. Otherwise, this paper may be better suited for a case-study oriented journal.
-One of the main conclusions is that recharge is not significantly affected by climate change. I think this result should be more extensively explained and discussed. For example, it would be useful to provide more details about how recharge is calculated. I understand the modeling has been detailed in previous papers, but the recharge calculations are central to the current paper, so they deserve special attention. This could be accompanied with more detailed results e.g. time-series of computed soil water balances and groundwater tables, to more clearly demonstrate where the increased rainfall ends up and why. This should also be accompanied by a more detailed discussion of the assumptions (are your recharge conclusions robust wrt model assumptions and chosen parameter values?). This should help clarify whether the small changes in recharge are related to the physical characteristics of the basin or to the way the model calculates recharge. Such an analysis can also increase the scientific value of the paper beyond the case study.
-I'm missing an aquifer water balance, this can be very useful to put the recharge and pumping values in perspective and to assess sustainability of the system under different scenarios.
-title: it's not the projections that will impact water availability, so better to change "future climate projections" to "future climate change" or "future groundwater recharge" (unless you actually mean that the projections will lead to decisions that will impact groundwater availability). Also, I would suggest to change "anthropogenic activities" to something more specific like "groundwater abstractions" or similar.
-line 101: to what extent is the aquitard spatially continuous?
-figure 1a: can you explain how the basin was delineated? is it based on topography?
-line 150: one-way coupling is justified if water tables are relatively far below land surface, is that the case here?
-line 168: "in each period"
-figure 2 could perhaps be simplified by only showing the workflow once but then with different climate and abstraction forcing
-line 181: the method for estimating potential ET is based on temperature and radiation and thus ignores potential changes in humidity and wind - can you justify this simplification or discuss its impact? Also, this method was apparently not developed for computing potential ET, so why is it applicable for this purpose?
-line 196: did you check that the surface shortwave radiation from MRI-ESM2-0 is consistent with that from GFDL-ESM4? Or alternatively explain why this comparison is not needed.
-line 230: are there any rain gauges in the area to check the assumption of treating CHIRPS as ground truth?
-line 250: river discharge I assume
-line 252-253: shouldn't you be using bias-corrected CMIP6 data for the historical period? Similar comment for figure 4: show the bias-corrected MRI-ESM2-0 for historical period instead of CHIRPS.
-line 274: what are the values for the storage parameters? and what are the "river-related parameters? Do the latter overlap with parameters in the wflow model?
-figure 5b: not clear what the extra horizontal lines are in this plot
-line 374: and much smaller storage coefficient in the confined aquifer?
-figure 7: make colorbar title and labels more readable
-line 416: do your simulations predict decreases in baseflow?
-line 479: what do you mean by "pseudo water table"?
-line 485: "In regions with higher margins between the groundwater recharge and soil capacity". Not clear, please clarify.
-check erroneous text on line 576
Citation: https://doi.org/10.5194/hess-2024-26-RC1 -
AC1: 'Reply on RC1', Steven Reinaldo Rusli, 09 May 2024
We extend our sincere gratitude for dedicating your time and effort to evaluating our manuscript. Additionally, we express appreciation for the favorable synopsis of our paper featured in the overarching review comments. Below, we meticulously address each of your inquiries and observations systematically:
Comments #1: Based on the introduction, novelty of the paper seems to be largely limited to the case study, since the literature review shows that very similar methodology has been used before with similar conclusions (groundwater abstractions more important than climate change). To justify publication in HESS the authors should strengthen the novelty description of their work in the introduction. Otherwise, this paper may be better suited for a case-study oriented journal.
Response #1: Thank you for your constructive feedback. We acknowledge the limitations of the previous iteration of the introduction, which exhibited an imbalance by predominantly referencing a singular perspective on the impact of climate change on groundwater resources. The prior manuscript predominantly highlighted studies aligning with the outcomes of our analysis, inadvertently neglecting research presenting divergent findings. The remarks provided have catalyzed a shift in our perspective, prompting us to recognize the significance of incorporating studies with disparate conclusions. By integrating these divergent studies into our revised introduction, we have elucidated the spatial variability inherent in the influence of climatic and anthropogenic factors on groundwater availability. This inclusion underscores the imperative of investigating this topic across various spatial scales—globally, regionally, and locally. We are confident that our revised manuscript adequately addresses your comments and enhances the comprehensiveness of our research.
Comment #2: One of the main conclusions is that recharge is not significantly affected by climate change. I think this result should be more extensively explained and discussed. For example, it would be useful to provide more details about how recharge is calculated. I understand the modeling has been detailed in previous papers, but the recharge calculations are central to the current paper, so they deserve special attention. This could be accompanied with more detailed results e.g. time-series of computed soil water balances and groundwater tables, to more clearly demonstrate where the increased rainfall ends up and why. This should also be accompanied by a more detailed discussion of the assumptions (are your recharge conclusions robust wrt model assumptions and chosen parameter values?). This should help clarify whether the small changes in recharge are related to the physical characteristics of the basin or to the way the model calculates recharge. Such an analysis can also increase the scientific value of the paper beyond the case study.
Response #2: Thank you very much for this great suggestion. In the current version of the manuscript, we have provided the clarity of this matter. First, we added the recharge calculation scheme within the used hydrological model in Section 2.4.2: Wflow_sbm model setup, particularly about MaxLeakage, the influencing model parameter that regulates the simulated groundwater recharge output. Then, we discuss the recharge generation process in both the results (3.2) and discussion (4.2) sections. We also, based on your suggestion, accompany the simulated groundwater recharge with more detailed results; we do it with the simulated river discharge and actual evaporation in the results section 3.2, shown in the new Figure 7 (attached as a supplement to this response). In lines 363 – 382, it is mentioned that the magnitude of groundwater recharge is relatively constant despite the increase in precipitation, as the rise of the forcing influx is reflected more so by the increase of river discharge as the outflow, and less so by the changes in groundwater storage, hence relatively constant groundwater recharge. The fact that both the median and the extreme values of the river discharge increase supports the notion that groundwater recharge is less affected by changes in climate variables (the quantitative values of this analysis are presented in the new Figures 7a and 7b). Your comment on the last sentence that suggests that this would increase the scientific value of the paper beyond the case study is also mentioned in the discussion section (4.2) Line 517 – 521, showing that both the hydrological modeling scheme and the basin’s physical characteristics, especially related to soil moisture capacity, plays an important role in recharge generation, regardless of the changes in the climate variables. Again, this is such a great suggestion, and we believe that the quality of our manuscript is greatly enhanced after incorporating this particular comment into it.
Comment #3: I'm missing an aquifer water balance, this can be very useful to put the recharge and pumping values in perspective and to assess sustainability of the system under different scenarios.
Response #3: Thank you for another great suggestion. We agree that the addition of aquifer water balance would be very useful to visualize the propagation of these two variables (recharge and abstraction) to the storage projection. A new figure on this visualization with its description is available in Section 3.4 (Groundwater storage projection). We also discuss it in Section 4.2 (Impact assessment on future groundwater level projection), as we can see from the additional new Figure 9 (also attached as a supplement to this response), that these times (between the years 2020 and 2025) are the crucial time as volumetric-wise, the annual groundwater abstraction is estimated to be at the cross-section with the total annual recharge. Once the groundwater recharge volume as the main inflow has been breached, it is going to be way more difficult to restore the basin’s groundwater storage condition, despite other fluxes involved (surface–groundwater interaction, for example).
Comment #4: title: it's not the projections that will impact water availability, so better to change "future climate projections" to "future climate change" or "future groundwater recharge" (unless you actually mean that the projections will lead to decisions that will impact groundwater availability). Also, I would suggest to change "anthropogenic activities" to something more specific like "groundwater abstractions" or similar.
Response #4: Thank you for your suggestion. We agree to change the title of our manuscript so it can describe the content more precisely to: ‘The impact of future changes in climate variables and groundwater abstraction on basin-scale groundwater availability’.
Comment #5: line 101: to what extent is the aquitard spatially continuous?
Response #5: Thank you for your question. Despite not being actually 100% continuous within the whole groundwater basin boundary, such a setup (of continuous thin aquitard layer) shown in the conceptual model (Figure 1b) is the dominant setting indicated in most of the data that we have. We derive our interpretation of the aquifer layering based on borehole data distributed across the basin, collated in previous studies (Rahiem, 2020) – mentioned in Section 2.4.3. We reported in our previous studies that these data are not uniformly distributed, especially in highly elevated areas. To fill in the gap of knowledge on the aquifer layering profile, we derive the conceptual model parsimoniously, and verify the assumption with the simulation results. This way, not only do we tackle the data sparsity by comparing the simulation results both qualitatively and quantitatively (reported in our previous studies), but we also verify our model assumption to define the aquitard as a continuous layer within the calculation. Despite a minority of the borehole data (~ 5%) does not show the aquitard layer in its soil stratigraphy, we believe our approach to simplifying the model setup in this setting is optimum in representing the basin subsurface physical characteristics. We do not explain all of this in the manuscript, because it is pretty extensive (this will take at least 15 to 20 additional lines), and it has been mentioned and discussed in our previous papers that we refer to in the manuscript.
Comment #6: figure 1a: can you explain how the basin was delineated? is it based on topography?
Response #6: Thank you for your question. In answering this (and the upcoming) question, first we apologize if we refer the answer a lot to our previous studies. To provide a short answer to the question, the groundwater basin shown in Figure 1a is delineated by considering two sources: (1) the official Indonesia government document on the boundaries of the groundwater basin and (2) surface topography MERIT-DEM (Yamazaki, et al, 2017). In the first document, it is stated that the groundwater basin is delineated based on the subsurface data that are collated by the government. Further information on the raw data used to delineate the basin was, unfortunately, not available/accessible. To verify its accuracy, we compare the groundwater basin delineation with the surface catchment area, and they are very similar (again, the comparison of these two boundaries was shown in our previous paper). To provide some minor adjustments considering some context and logical alignment between the surface and the subsurface basin, we incorporate the surface topography from the MERIT-DEM products to fine-tune the final groundwater basin boundary that we use in this study. MERIT-DEM is chosen as the benchmark for the sake of consistency, as we also use MERIT-DEM in our hydrological simulation using Wflow_sbm model.
Comment #7: line 150: one-way coupling is justified if water tables are relatively far below land surface, is that the case here?
Response #7: Thank you for your question. In our test basin, the surface elevation variation is large, causing the water table to also have a large variation. The lowest point in the basin is found at around 600 meters above sea level, while the highest point at around 2400 meters. Therefore, in the mountainous area, the water table is relatively far below the surface up to several tens of meters. On the other hand, in the lower elevated area, the water table varies from a couple of ten meters depth to close to the surface water as the boundaries (especially around the river). We address this limitation in our discussion, Line 517 – 521.
Comment #8: line 168: "in each period”
Response #8: Thank you for your suggestion. We have adjusted the manuscript accordingly.
Comment #9: figure 2 could perhaps be simplified by only showing the workflow once but then with different climate and abstraction forcing
Response #9: Thank you for your suggestion. We like the idea of simplifying the workflow, however, we also want to show the ‘repetitive’ nature of the simulation. By visualizing the workflow ‘twice’, we want to deliver the message that the model during the baseline simulation (the left part of the figure) has been calibrated and even reported in our previous studies, and the current manuscript is the application of the one-way coupled scheme to project the future groundwater availability under various scenario (the right part of the figure). We think that this message is harder to convey should we simplify the figure to just one workflow, therefore suggesting to keep the figure as it is. We hope you understand and are content with our reasoning.
Comment #10: line 181: the method for estimating potential ET is based on temperature and radiation and thus ignores potential changes in humidity and wind - can you justify this simplification or discuss its impact? Also, this method was apparently not developed for computing potential ET, so why is it applicable for this purpose?
Response #10: Thank you for your question. Indeed, considering the data limitation and uncertainties, we chose to involve methods in estimating PET to be simple. The justification is shown in the referred paper (de Bruin, et al. 2016), that the method is mostly confined to cases without local advection, which means that the local evaporation is not influenced as much by the moving moisture. As our study location is located in a ‘closed system’ (the Bandung area is basically a ‘bowl’ surrounded by mountains), the moisture taken away by the wind and humidity difference is insignificant, therefore allowing for the methods application in the area. In the same paper, it was also mentioned that the terminology potential evapotranspiration itself consists of multiple components, and our understanding of the term has evolved from time to time. Depending on the context of the usage, the methods can also be used to estimate the ‘so-called potential evapotranspiration’. There have been a lot of studies that use this method to estimate potential evapotranspiration too (Oudin, et al. 2005, Imhoff, et al. 2020, Gebremehdin, et al. 2022).
Comment #11: line 196: did you check that the surface shortwave radiation from MRI-ESM2-0 is consistent with that from GFDL-ESM4? Or alternatively explain why this comparison is not needed.
Response #11: Thank you for your question. We did check the surface shortwave radiation from MRI-ESM2-0 and compared them with ones from GFDL-ESM4. There are minor differences (obviously), in which the MRI-ESM2-0 projection results in slightly larger changes in future radiation. However, the effect of these differences in the following calculation is insignificant. First, the radiation is one variable among the other variables to compute the potential evapotranspiration (PET). Then, the PET is used not as a direct number/input in a calculation, but as the upper limit of the calculated actual evaporation. The actual evaporation then influences the magnitude of available water to flow as runoff or to infiltrate and further recharge the groundwater. These multi-steps computation process dissipates the influence initiated by the minor differences between the MRI-ESM2-0 and the GFDL-ESM4 projection radiation products.
Comment #12: line 230: are there any rain gauges in the area to check the assumption of treating CHIRPS as ground truth?
Response #12: Thank you for your question. Yes, there are 11 rainfall stations within and around the area. We have discussed and reported our analysis (in our previous study) on the rainfall estimates in the area by comparing numerous rainfall estimation methods: rainfall station measurement, satellite products, ground-corrected remote-sensing products, and interpolated rain gauge-based estimates. While the rainfall estimates measured by the rainfall stations are supposed to be the most accurate, they represent point measurement as opposed to areal estimates. Therefore, to derive the best estimate of the areal rainfall, we applied an uncertainty quantification method (Extended Triple Collocation method) in our previous study and concluded that CHIRPS could be used as the best estimate in representing the ground-truth areal rainfall. We did not provide a lengthy discussion on this matter in our manuscript, but it is shortly mentioned in Lines 264-265, Section 2.4.2: Wflow_sbm model setup.
Comment #13: line 250: river discharge I assume
Response #13: Thank you for your suggestion. We have adjusted the manuscript accordingly.
Comment #14: line 252-253: shouldn't you be using bias-corrected CMIP6 data for the historical period? Similar comment for figure 4: show the bias-corrected MRI-ESM2-0 for historical period instead of CHIRPS.
Response #14: Thank you for your suggestion. We intentionally use CHIRPS as we treat it to represent the ground-truth rainfall estimates. We also treat the following Figure 5 similarly: using ERA5 data as the ground-truth instead of bias-corrected MRI-ESM2-0 estimates. We would like to keep the consistency in all the figures, not only among these figures but also with Figure 2 (the one about the workflow mentioned above). In that figure, the workflow is ‘repeated’ between the left and the right part of the figure. The left part represents the simulation using the ‘ground-truth’ as the forcing and boundaries, while the right part represents the future projection. We also do not directly compare the ‘ground-truth’ with future projections in Figures 4 and 5, but apply the bias-correction beforehand, with the aim that these comparisons are referenced on the more similar (bias-corrected) yet consistent (with the previous figures) ground.
Comment #15: line 274: what are the values for the storage parameters? and what are the "river-related parameters? Do the latter overlap with parameters in the wflow model?
Response #15: Thank you for your question. The storage parameter includes the specific yield (sy) and specific storage (ss) of the unconfined and confined aquifer. The sy value is 0.2, and ss 8.7*10-3 /m. Again, this value has been reported in our previous studies referred to in the manuscript. The river-related parameters include river cell, riverbed hydraulic conductance, surface water elevation (as the head boundary to the groundwater), and the elevation of the bottom of the riverbed. We use different values as the cell size in the surface hydrology and groundwater flow models are different, but they represent similar conditions. For example, in the groundwater flow model, we could not specify the river width, as cells assigned as rivers have to have the whole cell treated as a stream. In reality, the cell width of 100 m is not always consistent with the actual river width, thus we adjust our parameterization in order to make them mathematically representative.
Comment #16: figure 5b: not clear what the extra horizontal lines are in this plot
Response #16: Thank you for your detailed review. The one in the boxplot is the surface downwelling shortwave radiation, while the one at the top (also in the boxplot, but very thin that they look like lines) is the top of atmosphere incident shortwave radiation. We have revised the figure accordingly to make it clear by adding a dashed line, separating the two mentioned ‘regions’ (the revised figure is also attached as a supplement to this response).
Comment #17: line 374: and much smaller storage coefficient in the confined aquifer?
Response #17: Thank you for your suggestion. We agree with your analysis on this matter, thus we have revised the manuscript accordingly.
Comment #18: figure 7: make colorbar title and labels more readable.
Response #18: Thank you for your suggestion. We have revised the now Figure 8 (there is an additional Figure 7 for the hydrological variables accompanying the groundwater recharge) accordingly by enlarging the size of the colorbar title and labels. The revised Figure 8 is also available as a supplement to this response.
Comment #19: line 416: do your simulations predict decreases in baseflow?
Response #19: We did not initially collect the baseflow simulation output intentionally. Thanks to the input from your previous suggestions of accompanying the groundwater recharge with other variables, we now have these values in hand. The groundwater level projections show that the least significant future groundwater table changes are found in the unconfined layer along the stream. This shows that the river baseflow is relatively constant. While this seems not to be a problem, the groundwater table in the unconfined storage actually depletes the most in the mountainous region, contributing to conserving the river baseflow due to the groundwater abstraction along the river downstream part. This is now added to the manuscript (shown above in the discussion part after the new figure showing the aquifer water balance components).
Comment #20: line 479: what do you mean by "pseudo water table"?
Response #20: Thank you for your question. As said in that particular section of the manuscript, ‘In the one-way model coupling setup, groundwater recharge is fully controlled by the surface processes and the pseudo-water table’. This sentence refers to the computational scheme of the hydrological model Wflow_sbm, where the soil is considered as a bucket with a certain depth and divided into saturated and unsaturated zones. The top of the saturated store represents the pseudo-water table. The formula and detailed description of all the Wflow_sbm parameters are now available online in this paper: van Verseveld, W. J., Weerts, A. H., Visser, M., Buitink, J., Imhoff, R. O., Boisgontier, H., Bouaziz, L., Eilander, D., Hegnauer, M., ten Velden, C., and Russell, B.: Wflow_sbm v0.7.3, a spatially distributed hydrological model: from global data to local applications, Geosci. Model Dev., 17, 3199–3234, https://doi.org/10.5194/gmd-17-3199-2024, 2024.
Comment #21: line 485: "In regions with higher margins between the groundwater recharge and soil capacity". Not clear, please clarify.
Response #21: Thank you for your question. In that section, we aimed to describe the circumstances where changes in climate variables would have a higher influence on the changes in groundwater recharge. According to the result in the test basin, the threshold for the water in the vadose zone to infiltrate as groundwater recharge is generally low; the vadose zone is relatively wet due to many factors: the surface processes, the continuous rainfall period, the soil characteristics, etc. Therefore, in regions with higher soil capacity and lower soil moisture, generally, there is a higher possibility of increasing groundwater recharge due to changes in climate variables. We hope that this explanation provides more clarity.
Comment #22: check erroneous text on line 576.
Response #22: Thank you for your detailed review. We have removed the text.
-
AC1: 'Reply on RC1', Steven Reinaldo Rusli, 09 May 2024
-
RC2: 'Comment on hess-2024-26', Anonymous Referee #2, 19 Apr 2024
General Comments
Dear Editors,
The manuscript deals with a very interesting theme not only for the scientific community but for the entire society, that of the comparison of the impact of projected climate forcing and anthropogenic activity on future groundwater status. I found the manuscript well written with a quite correct structure and I can say that someone can read it with pleasure. The study is quite interesting and actually, I have occupied with the same case in the past ending up with the same conclusions. For that reason, I deposit a few comments for the paper improvement.
Specific Comments
Lines 19-20: The authors indicate that there are many basins worldwide with over-exploited groundwater resources, but the references presented are only three (3). More references should be added to satisfy the word “worldwide”.
Chapter 2.1. No information is given about the water uses, the crop types, or the volumetric budget of the aquifers.
Figure 1b. The line of the cross-section AA’ should be presented in Figure 1a.
Line 109 “In recent years, the groundwater situation has not been improving” This is a very vague phrase and not properly stated. What does the word “situation” mean? I can understand very well the meaning of this sentence, but it needs to be rephrased to be more specific eg situation of what? The quantity? The quality?
Lines 238-250: I can understand that a full description of the hydrological model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters.
Lines 263-279: I can understand that a full description of the groundwater flow model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters the storage coefficient of the aquifers, the conductance of the hydraulic connection between the rives and the upper aquifer, the starting conditions, the period of simulation, the volumetric budget.
Lines 317-318: How do you explain the fact that the surface radiation reveals a tendency of a slight reduction in the future? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Figure 5.c. How do you explain the fact that the potential evapotranspiration reveals a reduction in the future, since the temperature increases? Furthermore why the potential evapotranspiration of RCP8.5 is lower than the one of the RCP4.5? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Chapter 3.3. The presentation of the results, although is very understandable and compact, is poor regarding both the size of the text and the use of the tables/graphs.
For example:
- In Lines 373-384 where the results of the the increasing groundwater abstraction scenario are presented, the results of 1) the RCP 4.5 scenario for the unconfined aquifer, 2) the RCP 8.5 scenario for both the two aquifers are missing. The phrase “Under the RCP8.5 scenario, the numbers are also concerning for the unconfined aquifers, as the groundwater table is projected to dwindle to up to 3.38 m and 3.40 m in the long run under the RCP4.5 and RCP8.5 scenarios, respectively” is not enough.
- The maps with the hydraulic head changes is a good and very useful choice but the results of the RCP 8.5 scenario and that of the other groundwater abstraction scenarios are not presented. I understand that many maps are needed for that reason, but the authors can focus on the presentation of the worst-case scenarios. There is no use in presenting the maps of Figures 7.a,b,c since the drawdown is not higher than one meter. I propose the authors find an extra way of representing the decline of the groundwater levels in relation to the time e.g. a line for each climatic and groundwater abstraction scenario (6 scenarios * 2 aquifers = 12 lines -like Fig.8) showing the decline of the groundwater level for that cell of aquifers that reveals the maximum drawdown. The same could be done for the drawdown area.
Lines 384-385: Why do you use the phrase “as expected”? It is not so obvious to the reader because the groundwater table decline was not presented in chapter 2.1. This result should be highlighted more and it should be made clear that even though the withdrawals do not increase the level will continue to fall and it should be explained why.
Citation: https://doi.org/10.5194/hess-2024-26-RC2 -
AC2: 'Reply on RC2', Steven Reinaldo Rusli, 09 May 2024
We extend our sincere gratitude for dedicating your time and effort to evaluating our manuscript. Additionally, we express appreciation for the favorable synopsis of our paper featured in the overarching review comments. Below, we meticulously address each of your inquiries and observations in a systematic manner:
Comment #1: Lines 19-20: The authors indicate that there are many basins worldwide with over-exploited groundwater resources, but the references presented are only three (3). More references should be added to satisfy the word “worldwide”.
Response #1: Thank you for your feedback. The references for the mentioned part are actually provided in the sentences after, and not in that particular sentence. We understand that to satisfy the word ‘worldwide’ is not an easy task, thus the entire paragraph is dedicated to supplying these examples (including the references). Following the Lines 19-20 as you mentioned, the example of basins with over-exploited groundwater is mentioned until Line 28 (Bangladesh, China, Brazil, and Spain were at least mentioned).
Comment #2: Chapter 2.1. No information is given about the water uses, the crop types, or the volumetric budget of the aquifers.
Response #2: Thank you for your feedback. The water uses in the study area are dominated by the domestic and industrial sectors. This information along with the volumetric budgets of the abstractions has been mentioned in Lines 93 – 97. We provided the more important details only in this study following the aim. The other details and quantifications on pre-baseline modeling variables are mentioned in our previous studies that we mentioned as references multiple times in the manuscript.
Comment #3: Figure 1b. The line of the cross-section AA’ should be presented in Figure 1a.
Response #3: Thank you for your suggestion. The figure has been adapted accordingly to your comment.
Comment #4: Line 109 “In recent years, the groundwater situation has not been improving” This is a very vague phrase and not properly stated. What does the word “situation” mean? I can understand very well the meaning of this sentence, but it needs to be rephrased to be more specific eg situation of what? The quantity? The quality?
Response #4: Thank you for your suggestion. We agree to change the phrasing accordingly. In the newer version, we are more direct and state what the ‘situation’ means, practically.
Comment #5: Lines 238-250: I can understand that a full description of the hydrological model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters.
Response #5: Thank you for your suggestion. We have added the information in that section, especially on the most important parameter named MaxLeakage which controls the amount of groundwater recharge in the hydrological simulation, specifically in Section 2.4.2: Wflow_sbm model setup.
Comment #6: Lines 263-279: I can understand that a full description of the groundwater flow model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters the storage coefficient of the aquifers, the conductance of the hydraulic connection between the rives and the upper aquifer, the starting conditions, the period of simulation, the volumetric budget.
Response #6: Thank you for your suggestion. We have quantified all the parameters and model settings you mentioned in the manuscript in Section 2.4.3: Groundwater flow model setup.
Comment #7: Lines 317-318: How do you explain the fact that the surface radiation reveals a tendency of a slight reduction in the future? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Response #7: Thank you for your question. The projected surface radiation, in our opinion, varies spatially. While some areas are expected to have increasing values, some others might be predicted to have decreasing values. For example, the projected cloud covers changes over time in different areas, therefore changing the radiation values. Thicker cloud covers would decrease the surface radiation, and vice versa. As per your suggestion to justify the decreasing values, here below are some references we found that support these numbers, where they found a decrease in future surface radiation projection:
- Ruosteenoja, K., Räisänen, P., Devraj, S., Garud, S. S., & Lindfors, A. V. (2019). Future Changes in Incident Surface Solar Radiation and Contributing Factors in India in CMIP5 Climate Model Simulations. Journal of Applied Meteorology and Climatology, 58(1), 19–35. https://www.jstor.org/stable/26679319
- Watanabe, S., K. Sudo, T. Nagashima, T. Takemura, H. Kawase, and T. Nozawa (2011), Future projections of surface UV-B in a changing climate, J. Geophys. Res., 116, D16118, doi:1029/2011JD015749.
- Martin Wild, Doris Folini, Florian Henschel, Natalie Fischer, Björn Müller. Projections of long-term changes in solar radiation based on CMIP5 climate models and their influence on energy yields of photovoltaic systems, Solar Energy, Volume 116, 2015, Pages 12-24, ISSN 0038-092X, https://doi.org/10.1016/j.solener.2015.03.039.
Comment #8: Figure 5.c. How do you explain the fact that the potential evapotranspiration reveals a reduction in the future, since the temperature increases? Furthermore why the potential evapotranspiration of RCP8.5 is lower than the one of the RCP4.5? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Response #8: Thank you for your question. The future potential evapotranspiration, as shown in Figure 5c, has a temporal variation according to its projection values. In some months, February to May and August to be specific, the PET actually increases and not decreases. It is 5 months among the 12 there are, so we would say that generalizing the PET value to be reduced is not representative of the results. About the comparison between the RCPs, they also vary for each month. For those periods where the PET of RCP8.5 is smaller, we would argue that the PET is controlled by variables other than temperature (e.g. radiation). Therefore, despite the temperature increases, the projection of other variables also plays an important role in determining the PET projection.
Comment #9:
Chapter 3.3. The presentation of the results, although is very understandable and compact, is poor regarding both the size of the text and the use of the tables/graphs.
For example:
- In Lines 373-384 where the results of the the increasing groundwater abstraction scenario are presented, the results of 1) the RCP 4.5 scenario for the unconfined aquifer, 2) the RCP 8.5 scenario for both the two aquifers are missing. The phrase “Under the RCP8.5 scenario, the numbers are also concerning for the unconfined aquifers, as the groundwater table is projected to dwindle to up to 3.38 m and 3.40 m in the long run under the RCP4.5 and RCP8.5 scenarios, respectively” is not enough.
- The maps with the hydraulic head changes is a good and very useful choice but the results of the RCP 8.5 scenario and that of the other groundwater abstraction scenarios are not presented. I understand that many maps are needed for that reason, but the authors can focus on the presentation of the worst-case scenarios. There is no use in presenting the maps of Figures 7.a,b,c since the drawdown is not higher than one meter. I propose the authors find an extra way of representing the decline of the groundwater levels in relation to the time e.g. a line for each climatic and groundwater abstraction scenario (6 scenarios * 2 aquifers = 12 lines -like Fig.8) showing the decline of the groundwater level for that cell of aquifers that reveals the maximum drawdown. The same could be done for the drawdown area.
Response #9: Thank you for your question. Indeed, there are a lot of numbers to unpack in Section 3.3. We were thinking of reporting all the numbers, but that would be tedious, not only to write but also to be read by the audience. Therefore, we focus on the extreme values in the text, and after discussing further until Line 406, we refer to Table 3 which summarizes all the values in one table, with the aim to make it easier to read. Meanwhile, about the figure where the drawdown is shown, we opted to show Figures a,b, and c, as they represent the unconfined aquifer in the short-, mid-, and long-term scenario. We very much want to have a representation in both layers of aquifers, and all three future checkpoints. We also put the results with the main aim to show the spatial distribution of the groundwater head change, and not the magnitude (although this is also interesting to see), because the magnitude is revealed in Table 3 (and Table 3 cannot visualize the spatial distribution of the changes).
Comment #10: Lines 384-385: Why do you use the phrase “as expected”? It is not so obvious to the reader because the groundwater table decline was not presented in chapter 2.1. This result should be highlighted more and it should be made clear that even though the withdrawals do not increase the level will continue to fall and it should be explained why.
Response #10: Thank you for your detailed comment. Indeed, we wrote that with our three previous papers in mind, so the word ‘as expected’ was written. We agree that to the reader, it is not so obvious, and that phrase should be removed. We have revised the part accordingly.
Citation: https://doi.org/10.5194/hess-2024-26-AC2
Status: closed
-
RC1: 'Comment on hess-2024-26', Anonymous Referee #1, 02 Apr 2024
The paper quantifies the impact of future climate change and changes in groundwater pumping on groundwater resources in the Bandung groundwater basin, Indonesia. This is done by driving a surface water and groundwater model with CMIP6 climate projections and various groundwater abstraction scenarios. Results show that groundwater abstraction has a larger impact on groundwater levels/storage than climate-induced changes in groundwater recharge.
The paper tackles an important and relevant topic and is generally well written. The following comments identify several points that deserve attention.
-Based on the introduction, novelty of the paper seems to be largely limited to the case study, since the literature review shows that very similar methodology has been used before with similar conclusions (groundwater abstractions more important than climate change). To justify publication in HESS the authors should strengthen the novelty description of their work in the introduction. Otherwise, this paper may be better suited for a case-study oriented journal.
-One of the main conclusions is that recharge is not significantly affected by climate change. I think this result should be more extensively explained and discussed. For example, it would be useful to provide more details about how recharge is calculated. I understand the modeling has been detailed in previous papers, but the recharge calculations are central to the current paper, so they deserve special attention. This could be accompanied with more detailed results e.g. time-series of computed soil water balances and groundwater tables, to more clearly demonstrate where the increased rainfall ends up and why. This should also be accompanied by a more detailed discussion of the assumptions (are your recharge conclusions robust wrt model assumptions and chosen parameter values?). This should help clarify whether the small changes in recharge are related to the physical characteristics of the basin or to the way the model calculates recharge. Such an analysis can also increase the scientific value of the paper beyond the case study.
-I'm missing an aquifer water balance, this can be very useful to put the recharge and pumping values in perspective and to assess sustainability of the system under different scenarios.
-title: it's not the projections that will impact water availability, so better to change "future climate projections" to "future climate change" or "future groundwater recharge" (unless you actually mean that the projections will lead to decisions that will impact groundwater availability). Also, I would suggest to change "anthropogenic activities" to something more specific like "groundwater abstractions" or similar.
-line 101: to what extent is the aquitard spatially continuous?
-figure 1a: can you explain how the basin was delineated? is it based on topography?
-line 150: one-way coupling is justified if water tables are relatively far below land surface, is that the case here?
-line 168: "in each period"
-figure 2 could perhaps be simplified by only showing the workflow once but then with different climate and abstraction forcing
-line 181: the method for estimating potential ET is based on temperature and radiation and thus ignores potential changes in humidity and wind - can you justify this simplification or discuss its impact? Also, this method was apparently not developed for computing potential ET, so why is it applicable for this purpose?
-line 196: did you check that the surface shortwave radiation from MRI-ESM2-0 is consistent with that from GFDL-ESM4? Or alternatively explain why this comparison is not needed.
-line 230: are there any rain gauges in the area to check the assumption of treating CHIRPS as ground truth?
-line 250: river discharge I assume
-line 252-253: shouldn't you be using bias-corrected CMIP6 data for the historical period? Similar comment for figure 4: show the bias-corrected MRI-ESM2-0 for historical period instead of CHIRPS.
-line 274: what are the values for the storage parameters? and what are the "river-related parameters? Do the latter overlap with parameters in the wflow model?
-figure 5b: not clear what the extra horizontal lines are in this plot
-line 374: and much smaller storage coefficient in the confined aquifer?
-figure 7: make colorbar title and labels more readable
-line 416: do your simulations predict decreases in baseflow?
-line 479: what do you mean by "pseudo water table"?
-line 485: "In regions with higher margins between the groundwater recharge and soil capacity". Not clear, please clarify.
-check erroneous text on line 576
Citation: https://doi.org/10.5194/hess-2024-26-RC1 -
AC1: 'Reply on RC1', Steven Reinaldo Rusli, 09 May 2024
We extend our sincere gratitude for dedicating your time and effort to evaluating our manuscript. Additionally, we express appreciation for the favorable synopsis of our paper featured in the overarching review comments. Below, we meticulously address each of your inquiries and observations systematically:
Comments #1: Based on the introduction, novelty of the paper seems to be largely limited to the case study, since the literature review shows that very similar methodology has been used before with similar conclusions (groundwater abstractions more important than climate change). To justify publication in HESS the authors should strengthen the novelty description of their work in the introduction. Otherwise, this paper may be better suited for a case-study oriented journal.
Response #1: Thank you for your constructive feedback. We acknowledge the limitations of the previous iteration of the introduction, which exhibited an imbalance by predominantly referencing a singular perspective on the impact of climate change on groundwater resources. The prior manuscript predominantly highlighted studies aligning with the outcomes of our analysis, inadvertently neglecting research presenting divergent findings. The remarks provided have catalyzed a shift in our perspective, prompting us to recognize the significance of incorporating studies with disparate conclusions. By integrating these divergent studies into our revised introduction, we have elucidated the spatial variability inherent in the influence of climatic and anthropogenic factors on groundwater availability. This inclusion underscores the imperative of investigating this topic across various spatial scales—globally, regionally, and locally. We are confident that our revised manuscript adequately addresses your comments and enhances the comprehensiveness of our research.
Comment #2: One of the main conclusions is that recharge is not significantly affected by climate change. I think this result should be more extensively explained and discussed. For example, it would be useful to provide more details about how recharge is calculated. I understand the modeling has been detailed in previous papers, but the recharge calculations are central to the current paper, so they deserve special attention. This could be accompanied with more detailed results e.g. time-series of computed soil water balances and groundwater tables, to more clearly demonstrate where the increased rainfall ends up and why. This should also be accompanied by a more detailed discussion of the assumptions (are your recharge conclusions robust wrt model assumptions and chosen parameter values?). This should help clarify whether the small changes in recharge are related to the physical characteristics of the basin or to the way the model calculates recharge. Such an analysis can also increase the scientific value of the paper beyond the case study.
Response #2: Thank you very much for this great suggestion. In the current version of the manuscript, we have provided the clarity of this matter. First, we added the recharge calculation scheme within the used hydrological model in Section 2.4.2: Wflow_sbm model setup, particularly about MaxLeakage, the influencing model parameter that regulates the simulated groundwater recharge output. Then, we discuss the recharge generation process in both the results (3.2) and discussion (4.2) sections. We also, based on your suggestion, accompany the simulated groundwater recharge with more detailed results; we do it with the simulated river discharge and actual evaporation in the results section 3.2, shown in the new Figure 7 (attached as a supplement to this response). In lines 363 – 382, it is mentioned that the magnitude of groundwater recharge is relatively constant despite the increase in precipitation, as the rise of the forcing influx is reflected more so by the increase of river discharge as the outflow, and less so by the changes in groundwater storage, hence relatively constant groundwater recharge. The fact that both the median and the extreme values of the river discharge increase supports the notion that groundwater recharge is less affected by changes in climate variables (the quantitative values of this analysis are presented in the new Figures 7a and 7b). Your comment on the last sentence that suggests that this would increase the scientific value of the paper beyond the case study is also mentioned in the discussion section (4.2) Line 517 – 521, showing that both the hydrological modeling scheme and the basin’s physical characteristics, especially related to soil moisture capacity, plays an important role in recharge generation, regardless of the changes in the climate variables. Again, this is such a great suggestion, and we believe that the quality of our manuscript is greatly enhanced after incorporating this particular comment into it.
Comment #3: I'm missing an aquifer water balance, this can be very useful to put the recharge and pumping values in perspective and to assess sustainability of the system under different scenarios.
Response #3: Thank you for another great suggestion. We agree that the addition of aquifer water balance would be very useful to visualize the propagation of these two variables (recharge and abstraction) to the storage projection. A new figure on this visualization with its description is available in Section 3.4 (Groundwater storage projection). We also discuss it in Section 4.2 (Impact assessment on future groundwater level projection), as we can see from the additional new Figure 9 (also attached as a supplement to this response), that these times (between the years 2020 and 2025) are the crucial time as volumetric-wise, the annual groundwater abstraction is estimated to be at the cross-section with the total annual recharge. Once the groundwater recharge volume as the main inflow has been breached, it is going to be way more difficult to restore the basin’s groundwater storage condition, despite other fluxes involved (surface–groundwater interaction, for example).
Comment #4: title: it's not the projections that will impact water availability, so better to change "future climate projections" to "future climate change" or "future groundwater recharge" (unless you actually mean that the projections will lead to decisions that will impact groundwater availability). Also, I would suggest to change "anthropogenic activities" to something more specific like "groundwater abstractions" or similar.
Response #4: Thank you for your suggestion. We agree to change the title of our manuscript so it can describe the content more precisely to: ‘The impact of future changes in climate variables and groundwater abstraction on basin-scale groundwater availability’.
Comment #5: line 101: to what extent is the aquitard spatially continuous?
Response #5: Thank you for your question. Despite not being actually 100% continuous within the whole groundwater basin boundary, such a setup (of continuous thin aquitard layer) shown in the conceptual model (Figure 1b) is the dominant setting indicated in most of the data that we have. We derive our interpretation of the aquifer layering based on borehole data distributed across the basin, collated in previous studies (Rahiem, 2020) – mentioned in Section 2.4.3. We reported in our previous studies that these data are not uniformly distributed, especially in highly elevated areas. To fill in the gap of knowledge on the aquifer layering profile, we derive the conceptual model parsimoniously, and verify the assumption with the simulation results. This way, not only do we tackle the data sparsity by comparing the simulation results both qualitatively and quantitatively (reported in our previous studies), but we also verify our model assumption to define the aquitard as a continuous layer within the calculation. Despite a minority of the borehole data (~ 5%) does not show the aquitard layer in its soil stratigraphy, we believe our approach to simplifying the model setup in this setting is optimum in representing the basin subsurface physical characteristics. We do not explain all of this in the manuscript, because it is pretty extensive (this will take at least 15 to 20 additional lines), and it has been mentioned and discussed in our previous papers that we refer to in the manuscript.
Comment #6: figure 1a: can you explain how the basin was delineated? is it based on topography?
Response #6: Thank you for your question. In answering this (and the upcoming) question, first we apologize if we refer the answer a lot to our previous studies. To provide a short answer to the question, the groundwater basin shown in Figure 1a is delineated by considering two sources: (1) the official Indonesia government document on the boundaries of the groundwater basin and (2) surface topography MERIT-DEM (Yamazaki, et al, 2017). In the first document, it is stated that the groundwater basin is delineated based on the subsurface data that are collated by the government. Further information on the raw data used to delineate the basin was, unfortunately, not available/accessible. To verify its accuracy, we compare the groundwater basin delineation with the surface catchment area, and they are very similar (again, the comparison of these two boundaries was shown in our previous paper). To provide some minor adjustments considering some context and logical alignment between the surface and the subsurface basin, we incorporate the surface topography from the MERIT-DEM products to fine-tune the final groundwater basin boundary that we use in this study. MERIT-DEM is chosen as the benchmark for the sake of consistency, as we also use MERIT-DEM in our hydrological simulation using Wflow_sbm model.
Comment #7: line 150: one-way coupling is justified if water tables are relatively far below land surface, is that the case here?
Response #7: Thank you for your question. In our test basin, the surface elevation variation is large, causing the water table to also have a large variation. The lowest point in the basin is found at around 600 meters above sea level, while the highest point at around 2400 meters. Therefore, in the mountainous area, the water table is relatively far below the surface up to several tens of meters. On the other hand, in the lower elevated area, the water table varies from a couple of ten meters depth to close to the surface water as the boundaries (especially around the river). We address this limitation in our discussion, Line 517 – 521.
Comment #8: line 168: "in each period”
Response #8: Thank you for your suggestion. We have adjusted the manuscript accordingly.
Comment #9: figure 2 could perhaps be simplified by only showing the workflow once but then with different climate and abstraction forcing
Response #9: Thank you for your suggestion. We like the idea of simplifying the workflow, however, we also want to show the ‘repetitive’ nature of the simulation. By visualizing the workflow ‘twice’, we want to deliver the message that the model during the baseline simulation (the left part of the figure) has been calibrated and even reported in our previous studies, and the current manuscript is the application of the one-way coupled scheme to project the future groundwater availability under various scenario (the right part of the figure). We think that this message is harder to convey should we simplify the figure to just one workflow, therefore suggesting to keep the figure as it is. We hope you understand and are content with our reasoning.
Comment #10: line 181: the method for estimating potential ET is based on temperature and radiation and thus ignores potential changes in humidity and wind - can you justify this simplification or discuss its impact? Also, this method was apparently not developed for computing potential ET, so why is it applicable for this purpose?
Response #10: Thank you for your question. Indeed, considering the data limitation and uncertainties, we chose to involve methods in estimating PET to be simple. The justification is shown in the referred paper (de Bruin, et al. 2016), that the method is mostly confined to cases without local advection, which means that the local evaporation is not influenced as much by the moving moisture. As our study location is located in a ‘closed system’ (the Bandung area is basically a ‘bowl’ surrounded by mountains), the moisture taken away by the wind and humidity difference is insignificant, therefore allowing for the methods application in the area. In the same paper, it was also mentioned that the terminology potential evapotranspiration itself consists of multiple components, and our understanding of the term has evolved from time to time. Depending on the context of the usage, the methods can also be used to estimate the ‘so-called potential evapotranspiration’. There have been a lot of studies that use this method to estimate potential evapotranspiration too (Oudin, et al. 2005, Imhoff, et al. 2020, Gebremehdin, et al. 2022).
Comment #11: line 196: did you check that the surface shortwave radiation from MRI-ESM2-0 is consistent with that from GFDL-ESM4? Or alternatively explain why this comparison is not needed.
Response #11: Thank you for your question. We did check the surface shortwave radiation from MRI-ESM2-0 and compared them with ones from GFDL-ESM4. There are minor differences (obviously), in which the MRI-ESM2-0 projection results in slightly larger changes in future radiation. However, the effect of these differences in the following calculation is insignificant. First, the radiation is one variable among the other variables to compute the potential evapotranspiration (PET). Then, the PET is used not as a direct number/input in a calculation, but as the upper limit of the calculated actual evaporation. The actual evaporation then influences the magnitude of available water to flow as runoff or to infiltrate and further recharge the groundwater. These multi-steps computation process dissipates the influence initiated by the minor differences between the MRI-ESM2-0 and the GFDL-ESM4 projection radiation products.
Comment #12: line 230: are there any rain gauges in the area to check the assumption of treating CHIRPS as ground truth?
Response #12: Thank you for your question. Yes, there are 11 rainfall stations within and around the area. We have discussed and reported our analysis (in our previous study) on the rainfall estimates in the area by comparing numerous rainfall estimation methods: rainfall station measurement, satellite products, ground-corrected remote-sensing products, and interpolated rain gauge-based estimates. While the rainfall estimates measured by the rainfall stations are supposed to be the most accurate, they represent point measurement as opposed to areal estimates. Therefore, to derive the best estimate of the areal rainfall, we applied an uncertainty quantification method (Extended Triple Collocation method) in our previous study and concluded that CHIRPS could be used as the best estimate in representing the ground-truth areal rainfall. We did not provide a lengthy discussion on this matter in our manuscript, but it is shortly mentioned in Lines 264-265, Section 2.4.2: Wflow_sbm model setup.
Comment #13: line 250: river discharge I assume
Response #13: Thank you for your suggestion. We have adjusted the manuscript accordingly.
Comment #14: line 252-253: shouldn't you be using bias-corrected CMIP6 data for the historical period? Similar comment for figure 4: show the bias-corrected MRI-ESM2-0 for historical period instead of CHIRPS.
Response #14: Thank you for your suggestion. We intentionally use CHIRPS as we treat it to represent the ground-truth rainfall estimates. We also treat the following Figure 5 similarly: using ERA5 data as the ground-truth instead of bias-corrected MRI-ESM2-0 estimates. We would like to keep the consistency in all the figures, not only among these figures but also with Figure 2 (the one about the workflow mentioned above). In that figure, the workflow is ‘repeated’ between the left and the right part of the figure. The left part represents the simulation using the ‘ground-truth’ as the forcing and boundaries, while the right part represents the future projection. We also do not directly compare the ‘ground-truth’ with future projections in Figures 4 and 5, but apply the bias-correction beforehand, with the aim that these comparisons are referenced on the more similar (bias-corrected) yet consistent (with the previous figures) ground.
Comment #15: line 274: what are the values for the storage parameters? and what are the "river-related parameters? Do the latter overlap with parameters in the wflow model?
Response #15: Thank you for your question. The storage parameter includes the specific yield (sy) and specific storage (ss) of the unconfined and confined aquifer. The sy value is 0.2, and ss 8.7*10-3 /m. Again, this value has been reported in our previous studies referred to in the manuscript. The river-related parameters include river cell, riverbed hydraulic conductance, surface water elevation (as the head boundary to the groundwater), and the elevation of the bottom of the riverbed. We use different values as the cell size in the surface hydrology and groundwater flow models are different, but they represent similar conditions. For example, in the groundwater flow model, we could not specify the river width, as cells assigned as rivers have to have the whole cell treated as a stream. In reality, the cell width of 100 m is not always consistent with the actual river width, thus we adjust our parameterization in order to make them mathematically representative.
Comment #16: figure 5b: not clear what the extra horizontal lines are in this plot
Response #16: Thank you for your detailed review. The one in the boxplot is the surface downwelling shortwave radiation, while the one at the top (also in the boxplot, but very thin that they look like lines) is the top of atmosphere incident shortwave radiation. We have revised the figure accordingly to make it clear by adding a dashed line, separating the two mentioned ‘regions’ (the revised figure is also attached as a supplement to this response).
Comment #17: line 374: and much smaller storage coefficient in the confined aquifer?
Response #17: Thank you for your suggestion. We agree with your analysis on this matter, thus we have revised the manuscript accordingly.
Comment #18: figure 7: make colorbar title and labels more readable.
Response #18: Thank you for your suggestion. We have revised the now Figure 8 (there is an additional Figure 7 for the hydrological variables accompanying the groundwater recharge) accordingly by enlarging the size of the colorbar title and labels. The revised Figure 8 is also available as a supplement to this response.
Comment #19: line 416: do your simulations predict decreases in baseflow?
Response #19: We did not initially collect the baseflow simulation output intentionally. Thanks to the input from your previous suggestions of accompanying the groundwater recharge with other variables, we now have these values in hand. The groundwater level projections show that the least significant future groundwater table changes are found in the unconfined layer along the stream. This shows that the river baseflow is relatively constant. While this seems not to be a problem, the groundwater table in the unconfined storage actually depletes the most in the mountainous region, contributing to conserving the river baseflow due to the groundwater abstraction along the river downstream part. This is now added to the manuscript (shown above in the discussion part after the new figure showing the aquifer water balance components).
Comment #20: line 479: what do you mean by "pseudo water table"?
Response #20: Thank you for your question. As said in that particular section of the manuscript, ‘In the one-way model coupling setup, groundwater recharge is fully controlled by the surface processes and the pseudo-water table’. This sentence refers to the computational scheme of the hydrological model Wflow_sbm, where the soil is considered as a bucket with a certain depth and divided into saturated and unsaturated zones. The top of the saturated store represents the pseudo-water table. The formula and detailed description of all the Wflow_sbm parameters are now available online in this paper: van Verseveld, W. J., Weerts, A. H., Visser, M., Buitink, J., Imhoff, R. O., Boisgontier, H., Bouaziz, L., Eilander, D., Hegnauer, M., ten Velden, C., and Russell, B.: Wflow_sbm v0.7.3, a spatially distributed hydrological model: from global data to local applications, Geosci. Model Dev., 17, 3199–3234, https://doi.org/10.5194/gmd-17-3199-2024, 2024.
Comment #21: line 485: "In regions with higher margins between the groundwater recharge and soil capacity". Not clear, please clarify.
Response #21: Thank you for your question. In that section, we aimed to describe the circumstances where changes in climate variables would have a higher influence on the changes in groundwater recharge. According to the result in the test basin, the threshold for the water in the vadose zone to infiltrate as groundwater recharge is generally low; the vadose zone is relatively wet due to many factors: the surface processes, the continuous rainfall period, the soil characteristics, etc. Therefore, in regions with higher soil capacity and lower soil moisture, generally, there is a higher possibility of increasing groundwater recharge due to changes in climate variables. We hope that this explanation provides more clarity.
Comment #22: check erroneous text on line 576.
Response #22: Thank you for your detailed review. We have removed the text.
-
AC1: 'Reply on RC1', Steven Reinaldo Rusli, 09 May 2024
-
RC2: 'Comment on hess-2024-26', Anonymous Referee #2, 19 Apr 2024
General Comments
Dear Editors,
The manuscript deals with a very interesting theme not only for the scientific community but for the entire society, that of the comparison of the impact of projected climate forcing and anthropogenic activity on future groundwater status. I found the manuscript well written with a quite correct structure and I can say that someone can read it with pleasure. The study is quite interesting and actually, I have occupied with the same case in the past ending up with the same conclusions. For that reason, I deposit a few comments for the paper improvement.
Specific Comments
Lines 19-20: The authors indicate that there are many basins worldwide with over-exploited groundwater resources, but the references presented are only three (3). More references should be added to satisfy the word “worldwide”.
Chapter 2.1. No information is given about the water uses, the crop types, or the volumetric budget of the aquifers.
Figure 1b. The line of the cross-section AA’ should be presented in Figure 1a.
Line 109 “In recent years, the groundwater situation has not been improving” This is a very vague phrase and not properly stated. What does the word “situation” mean? I can understand very well the meaning of this sentence, but it needs to be rephrased to be more specific eg situation of what? The quantity? The quality?
Lines 238-250: I can understand that a full description of the hydrological model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters.
Lines 263-279: I can understand that a full description of the groundwater flow model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters the storage coefficient of the aquifers, the conductance of the hydraulic connection between the rives and the upper aquifer, the starting conditions, the period of simulation, the volumetric budget.
Lines 317-318: How do you explain the fact that the surface radiation reveals a tendency of a slight reduction in the future? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Figure 5.c. How do you explain the fact that the potential evapotranspiration reveals a reduction in the future, since the temperature increases? Furthermore why the potential evapotranspiration of RCP8.5 is lower than the one of the RCP4.5? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Chapter 3.3. The presentation of the results, although is very understandable and compact, is poor regarding both the size of the text and the use of the tables/graphs.
For example:
- In Lines 373-384 where the results of the the increasing groundwater abstraction scenario are presented, the results of 1) the RCP 4.5 scenario for the unconfined aquifer, 2) the RCP 8.5 scenario for both the two aquifers are missing. The phrase “Under the RCP8.5 scenario, the numbers are also concerning for the unconfined aquifers, as the groundwater table is projected to dwindle to up to 3.38 m and 3.40 m in the long run under the RCP4.5 and RCP8.5 scenarios, respectively” is not enough.
- The maps with the hydraulic head changes is a good and very useful choice but the results of the RCP 8.5 scenario and that of the other groundwater abstraction scenarios are not presented. I understand that many maps are needed for that reason, but the authors can focus on the presentation of the worst-case scenarios. There is no use in presenting the maps of Figures 7.a,b,c since the drawdown is not higher than one meter. I propose the authors find an extra way of representing the decline of the groundwater levels in relation to the time e.g. a line for each climatic and groundwater abstraction scenario (6 scenarios * 2 aquifers = 12 lines -like Fig.8) showing the decline of the groundwater level for that cell of aquifers that reveals the maximum drawdown. The same could be done for the drawdown area.
Lines 384-385: Why do you use the phrase “as expected”? It is not so obvious to the reader because the groundwater table decline was not presented in chapter 2.1. This result should be highlighted more and it should be made clear that even though the withdrawals do not increase the level will continue to fall and it should be explained why.
Citation: https://doi.org/10.5194/hess-2024-26-RC2 -
AC2: 'Reply on RC2', Steven Reinaldo Rusli, 09 May 2024
We extend our sincere gratitude for dedicating your time and effort to evaluating our manuscript. Additionally, we express appreciation for the favorable synopsis of our paper featured in the overarching review comments. Below, we meticulously address each of your inquiries and observations in a systematic manner:
Comment #1: Lines 19-20: The authors indicate that there are many basins worldwide with over-exploited groundwater resources, but the references presented are only three (3). More references should be added to satisfy the word “worldwide”.
Response #1: Thank you for your feedback. The references for the mentioned part are actually provided in the sentences after, and not in that particular sentence. We understand that to satisfy the word ‘worldwide’ is not an easy task, thus the entire paragraph is dedicated to supplying these examples (including the references). Following the Lines 19-20 as you mentioned, the example of basins with over-exploited groundwater is mentioned until Line 28 (Bangladesh, China, Brazil, and Spain were at least mentioned).
Comment #2: Chapter 2.1. No information is given about the water uses, the crop types, or the volumetric budget of the aquifers.
Response #2: Thank you for your feedback. The water uses in the study area are dominated by the domestic and industrial sectors. This information along with the volumetric budgets of the abstractions has been mentioned in Lines 93 – 97. We provided the more important details only in this study following the aim. The other details and quantifications on pre-baseline modeling variables are mentioned in our previous studies that we mentioned as references multiple times in the manuscript.
Comment #3: Figure 1b. The line of the cross-section AA’ should be presented in Figure 1a.
Response #3: Thank you for your suggestion. The figure has been adapted accordingly to your comment.
Comment #4: Line 109 “In recent years, the groundwater situation has not been improving” This is a very vague phrase and not properly stated. What does the word “situation” mean? I can understand very well the meaning of this sentence, but it needs to be rephrased to be more specific eg situation of what? The quantity? The quality?
Response #4: Thank you for your suggestion. We agree to change the phrasing accordingly. In the newer version, we are more direct and state what the ‘situation’ means, practically.
Comment #5: Lines 238-250: I can understand that a full description of the hydrological model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters.
Response #5: Thank you for your suggestion. We have added the information in that section, especially on the most important parameter named MaxLeakage which controls the amount of groundwater recharge in the hydrological simulation, specifically in Section 2.4.2: Wflow_sbm model setup.
Comment #6: Lines 263-279: I can understand that a full description of the groundwater flow model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters the storage coefficient of the aquifers, the conductance of the hydraulic connection between the rives and the upper aquifer, the starting conditions, the period of simulation, the volumetric budget.
Response #6: Thank you for your suggestion. We have quantified all the parameters and model settings you mentioned in the manuscript in Section 2.4.3: Groundwater flow model setup.
Comment #7: Lines 317-318: How do you explain the fact that the surface radiation reveals a tendency of a slight reduction in the future? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Response #7: Thank you for your question. The projected surface radiation, in our opinion, varies spatially. While some areas are expected to have increasing values, some others might be predicted to have decreasing values. For example, the projected cloud covers changes over time in different areas, therefore changing the radiation values. Thicker cloud covers would decrease the surface radiation, and vice versa. As per your suggestion to justify the decreasing values, here below are some references we found that support these numbers, where they found a decrease in future surface radiation projection:
- Ruosteenoja, K., Räisänen, P., Devraj, S., Garud, S. S., & Lindfors, A. V. (2019). Future Changes in Incident Surface Solar Radiation and Contributing Factors in India in CMIP5 Climate Model Simulations. Journal of Applied Meteorology and Climatology, 58(1), 19–35. https://www.jstor.org/stable/26679319
- Watanabe, S., K. Sudo, T. Nagashima, T. Takemura, H. Kawase, and T. Nozawa (2011), Future projections of surface UV-B in a changing climate, J. Geophys. Res., 116, D16118, doi:1029/2011JD015749.
- Martin Wild, Doris Folini, Florian Henschel, Natalie Fischer, Björn Müller. Projections of long-term changes in solar radiation based on CMIP5 climate models and their influence on energy yields of photovoltaic systems, Solar Energy, Volume 116, 2015, Pages 12-24, ISSN 0038-092X, https://doi.org/10.1016/j.solener.2015.03.039.
Comment #8: Figure 5.c. How do you explain the fact that the potential evapotranspiration reveals a reduction in the future, since the temperature increases? Furthermore why the potential evapotranspiration of RCP8.5 is lower than the one of the RCP4.5? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Response #8: Thank you for your question. The future potential evapotranspiration, as shown in Figure 5c, has a temporal variation according to its projection values. In some months, February to May and August to be specific, the PET actually increases and not decreases. It is 5 months among the 12 there are, so we would say that generalizing the PET value to be reduced is not representative of the results. About the comparison between the RCPs, they also vary for each month. For those periods where the PET of RCP8.5 is smaller, we would argue that the PET is controlled by variables other than temperature (e.g. radiation). Therefore, despite the temperature increases, the projection of other variables also plays an important role in determining the PET projection.
Comment #9:
Chapter 3.3. The presentation of the results, although is very understandable and compact, is poor regarding both the size of the text and the use of the tables/graphs.
For example:
- In Lines 373-384 where the results of the the increasing groundwater abstraction scenario are presented, the results of 1) the RCP 4.5 scenario for the unconfined aquifer, 2) the RCP 8.5 scenario for both the two aquifers are missing. The phrase “Under the RCP8.5 scenario, the numbers are also concerning for the unconfined aquifers, as the groundwater table is projected to dwindle to up to 3.38 m and 3.40 m in the long run under the RCP4.5 and RCP8.5 scenarios, respectively” is not enough.
- The maps with the hydraulic head changes is a good and very useful choice but the results of the RCP 8.5 scenario and that of the other groundwater abstraction scenarios are not presented. I understand that many maps are needed for that reason, but the authors can focus on the presentation of the worst-case scenarios. There is no use in presenting the maps of Figures 7.a,b,c since the drawdown is not higher than one meter. I propose the authors find an extra way of representing the decline of the groundwater levels in relation to the time e.g. a line for each climatic and groundwater abstraction scenario (6 scenarios * 2 aquifers = 12 lines -like Fig.8) showing the decline of the groundwater level for that cell of aquifers that reveals the maximum drawdown. The same could be done for the drawdown area.
Response #9: Thank you for your question. Indeed, there are a lot of numbers to unpack in Section 3.3. We were thinking of reporting all the numbers, but that would be tedious, not only to write but also to be read by the audience. Therefore, we focus on the extreme values in the text, and after discussing further until Line 406, we refer to Table 3 which summarizes all the values in one table, with the aim to make it easier to read. Meanwhile, about the figure where the drawdown is shown, we opted to show Figures a,b, and c, as they represent the unconfined aquifer in the short-, mid-, and long-term scenario. We very much want to have a representation in both layers of aquifers, and all three future checkpoints. We also put the results with the main aim to show the spatial distribution of the groundwater head change, and not the magnitude (although this is also interesting to see), because the magnitude is revealed in Table 3 (and Table 3 cannot visualize the spatial distribution of the changes).
Comment #10: Lines 384-385: Why do you use the phrase “as expected”? It is not so obvious to the reader because the groundwater table decline was not presented in chapter 2.1. This result should be highlighted more and it should be made clear that even though the withdrawals do not increase the level will continue to fall and it should be explained why.
Response #10: Thank you for your detailed comment. Indeed, we wrote that with our three previous papers in mind, so the word ‘as expected’ was written. We agree that to the reader, it is not so obvious, and that phrase should be removed. We have revised the part accordingly.
Citation: https://doi.org/10.5194/hess-2024-26-AC2
Data sets
Data and models used for paper 'The impact of future climate projections and anthropogenic activities on basin-scale groundwater availability' Steven Rusli, Victor Bense, Syed Mustafa, and Albrecht Weerts https://doi.org/10.4121/d9706a2a-b77b-412f-a3aa-6e22bd8ddf4a
Viewed
HTML | XML | Total | BibTeX | EndNote | |
---|---|---|---|---|---|
560 | 164 | 34 | 758 | 26 | 33 |
- HTML: 560
- PDF: 164
- XML: 34
- Total: 758
- BibTeX: 26
- EndNote: 33
Viewed (geographical distribution)
Country | # | Views | % |
---|
Total: | 0 |
HTML: | 0 |
PDF: | 0 |
XML: | 0 |
- 1