the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Oct 2024
Dams extend the surface water renewal time in inland river basins: A comparative study based on stable isotope data from two different basin
Abstract. The dramatic increase in the number of dams on rivers in recent years have led to a more complicated water circulation mechanism in arid regions, Capturing the impact of dams on water circulation processes is an ongoing challenge in the hydrology field. By utilizing observational isotopic data from water bodies, we conducted a comparative study on the Fyw and MTT in two inland river basins within the arid zone of Central Asia. Research findings suggest that dams amplify the damping effect and phase shift of seasonal fluctuations in river water, which in turn extends the water circulation period within inland river basins. The cascading interception of river water by dams has substantially reduced the proportion of young water (Fyw) in the river and has nearly tripled the mean transit time (MTT) of river water. This work confirms the fact that dams are profoundly influencing the water circulation processes in inland river basins from an isotopic kinetic perspective, and is useful for understanding the mechanisms driving water circulation times arid areas.
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RC1: 'Comment on hess-2024-277', Anonymous Referee #1, 19 Nov 2024
This is potentially an interesting study but, as written, this paper falls short of what is required for publication in a major international journal such as HESS. I have provided several general comments but have not gone through some of the sections (the results or regional setting) in detail as the basis of the paper needs serious attention. In its current form, presenting results with little discussion or explanation (and not outlining what is novel) is unlikely to create interest with a broad international readership. I understand that getting negative results is never pleasant, but I hope that these comments help in revising the study.
Here are the general issues with the paper.
Firstly, there is a general lack of explanation such that the reader cannot easily follow aspects of the text . The paper is relatively short; however, the brevity has been achieved at the expense of clarity and rigor. For example, lines 51-75 present the general the technical background and this section needs to convey to the reader the important background and identify knowledge gaps, problems, or contrasting approaches. However, it falls short of this, for example:
1) L54-58. Some broader discussion of mean transit times and the issues around these would be useful.
2) Likewise, you should define what the young water fraction is and why it is important. The approach of determining Fwy rather than a mean transit time is due to flow systems not being stationary (which is an assumption in much of the early work using tracers such as stable isotopes to determine MTTs). This is well discussed in Kirchner (2016) and Jasechko et al. (2016), both of which you cite.
3) Statements such as: “There are a number of factors influencing the water transit times” (L66) need explaining – what are they and how do they impact MTTs?
4) The Methods (Section 3) are also brief and a bit more detail on lumped parameter models (especially the gamma model, which is the one that you choose) is also needed.
Secondly, the calculations need to be more rigorous and thought through more. The basic outline of the calculations is presented in Section 3.2 and Section 5 presents the calculated results. However, nowhere is there any real discission of the results. Specifically:
5) You choose to estimate MTTs as well as Fwy but part of the reason for using Fwy is due to the stationarity problem that was identified by Kirchner (2016). Briefly that is that the assumption made when using LPMs with seasonal tracers that the flow system does not change over the year such the MTT is constant at all flows. However, the reality is that catchments discharge younger water during wetter conditions and older water during dry periods. Studies using tracers such as tritium (e.g. Cartwright et al., 2020, which you cite) and studies using other techniques such as flux tracking (e.g. Hrachowit et al., 2013. Hydrology and Earth System Sciences, 17, 533–564. https://doi.org/10.5194/hess-17-533-2013) or StorAge solutions (Benettin et al., 2015 Water Resources Research, 51, 9256–9272. https://doi.org/10.1002/2014WR016600) also show this. Given that this issue is implicitly recognised, is it really valid to calculate MTTs using a lumped parameter model?
6) If you do use a lumped parameter model, you need to discuss some of the associated potential problems, such as:
- Aggregation (i.e. macroscopic mixing from different sources); this is discussed in Kirchner (2016, Hydrol. Earth Syst. Sci., 20, 279–297, https://doi.org/10.5194/hess-20-279-2016).
- Truncation, which is the possibility that there is older water with an attenuated signal, such that the MTTs are underestimated (e.g. Stewart, et al., 2010, Hydrol. Process. 24, 1646–1659. https://doi.org/10.1002/hyp.7576). Given the longest MTTs you estimate are >9 years, this is likely to be a significant issue.
7) What are the parameters in the gamma model and why where they chosen? The transit time distributions in this model vary with the alpha parameter (e.g. Stewart et al., 2017. Hydrol. Earth Syst. Sci., 21, 4615–4627, https://doi.org/10.5194/hess-21-4615-2017 ) and the calculated MTT also varies. It looks like you have used only a single parameterisation but there are not details of which one and why it was chosen. Is there any advantage of using the gamma model over say the exponential or exponential-piston flow lumped parameter models or the dispersion model (which like the gamma model is fairly generic)
8) Uncertainties are discussed (Sections 5.1 and 5.3), but it is not always clear what was taken into account. Statements such as “As the spatial and temporal heterogeneity of the basin may cause errors in the MTT estimates, we used Fyw to constrain the estimated MTT results” are not very clear. There are several uncertainties that should be included, such as:
- Uncertainties arising from the derivation of the input function. Figure 3 shows that there is a decent sinusoidal variation in the precipitation isotopes, and that the fitted curve is reasonable but there will still be an uncertainty here that translates into errors in Fyw and MTTs
- The impacts of varying the parameters in the lumped parameter models
- Aggregation and truncation
The papers that you cite plus the ones also referred to here have a far higher lever of rigor than you have attempted and the results come across as being far more convincing.
Finally, I am not convinced about the importance and novelty of the study.
- Concluding that water transit times in dammed catchments are longer would seem unsurprising (the reservoirs behind the dams have a storage time that is longer than the storage time in a free-flowing river after all). So, what is the new understanding here?
- Are there other studies with which you can compare this work (which would place it in a better international context)? If it is the first such study, then discuss that and perhaps do more justification that the calculations can apply to heavily modified rivers that are more susceptible to evaporation which obviously modifies the stable isotopes.
Citation: https://doi.org/10.5194/hess-2024-277-RC1 -
AC1: 'Reply on RC1', Guofeng Zhu, 26 Feb 2025
Author responses
Thank you very much for your E-mail of December 30th, 2024. We appreciate the editor and reviewer′s constructive comments and suggestions for our manuscript entitled “Dams extend the surface water renewal time in inland river basins: A comparative study based on stable isotope data from two different basin” with the reference HESS-2024-277
According to the reviewer's comments, we have revised our manuscript carefully. The revised portions have been marked in red in the manuscript track changes version. The main corrections and the response to the reviewer′s comments are as follows.
Responses to the reviewer’s comments
Response to Reviewer #1
- Clarity and Rigor of the Paper
Reviewer’s Comment:
The paper lacks sufficient explanation, making it difficult for readers to follow certain sections. Specifically, the technical background (e.g., L54-58) does not adequately discuss mean transit times (MTTs), and the definition of the young water fraction (Fyw) and its importance are not clearly stated.
Response and Revisions:
We have expanded the discussion of MTT and Fyw in the Introduction section. The following changes were made:
Discussion of MTT: In L54-58, we added a detailed explanation of MTT, its significance in hydrological studies, and references to McGuire and McDonnell (2006) and Hrachowitz et al. (2009), emphasizing the role of MTT in understanding catchment hydrological functions.
Definition and Importance of Fyw: In L60-65, we clarified the concept of Fyw and its application in non-stationary catchments, citing Kirchner (2016) and Jasechko et al. (2016) to highlight the unique advantages of Fyw in assessing hydrological responses.
Reviewer’s Comment:
The statement “There are a number of factors influencing water transit times” (L66) requires further elaboration.
Response and Revisions:
In L66-70, we elaborated on the key factors influencing water transit times, including natural factors (e.g., vegetation cover, catchment area) and anthropogenic factors (e.g., dam construction), citing Cartwright et al. (2020) and Weiler et al. (2003) to discuss how these factors impact MTTs.
- Detail and Rigor of the Methods
Reviewer’s Comment:
The Methods section is too brief, particularly regarding the lumped parameter models (e.g., the gamma model).
Response and Revisions:
We have expanded Section 3.2 to include a detailed description of the gamma model, its mathematical formulation, parameter selection, and its application in hydrological studies. The following changes were made:
Parameter Selection for the Gamma Model: In L155-160, we explained the significance of the α and β parameters and their influence on transit time distributions, citing Stewart et al. (2017) to justify our parameter choices.
Model Uncertainties: In L165-170, we discussed potential issues with the gamma model, such as aggregation and truncation effects, and referenced Kirchner (2016) and Stewart et al. (2010) to explain how Fyw was used to constrain MTT estimates.
- Discussion and Interpretation of Results
Reviewer’s Comment:
The Results section lacks in-depth discussion and fails to highlight the novelty and international significance of the study.
Response and Revisions:
We have expanded Section 5 to include a detailed discussion of the results, particularly the impact of dams on water transit times and the international context of the study. The following changes were made:
Impact of Dams on Water Transit Times: In L260-270, we compared our findings with global studies (e.g., Lehner et al., 2011; Zarfl et al., 2015) to discuss how dams prolong water transit times through interception and evaporation, emphasizing the unique contribution of this study in arid inland river basins.
Novelty of the Study: In L330-340, we highlighted that this study is the first to quantitatively assess the impact of dams on water cycle times from an isotope dynamics perspective and discussed its potential applications in global water cycle research.
- Discussion of Uncertainties
Reviewer’s Comment:
The discussion of uncertainties is incomplete, particularly regarding the derivation of the input function and the impact of varying model parameters.
Response and Revisions:
We have expanded Section 5.3 to include a detailed analysis of uncertainties. The following changes were made:
Uncertainties in the Input Function: In L305-310, we discussed the influence of seasonal variations in precipitation isotope data on Fyw and MTT estimates, citing Stockinger et al. (2016) to emphasize the importance of high sampling frequency in improving result accuracy.
Uncertainties in Model Parameters: In L315-320, we analyzed the impact of varying α and β parameters on MTT estimates and referenced Hrachowitz et al. (2011) to explain how the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to quantify model uncertainties.
- International Context and Significance of the Study
Reviewer’s Comment:
The conclusion that dams prolong water transit times is unsurprising, and the study lacks sufficient comparison with other research.
Response and Revisions:
We have expanded Section 6 to include a discussion of the international context of the study. The following changes were made:
Comparison with Other Studies: In L345-355, we compared our findings with global research (e.g., Vörösmarty et al., 1997; Wang et al., 2019) to highlight the similarities and differences, emphasizing the unique contribution of this study in arid inland river basins.
Significance of the Study: In L360-370, we discussed the potential implications of this study for global water cycle research, particularly in guiding water resource management in arid regions.
Citation: https://doi.org/10.5194/hess-2024-277-AC1
-
RC2: 'Comment on hess-2024-277', Anonymous Referee #2, 29 Dec 2024
The authors try to investigate the effects of dams and are using stable water isotopes to achieve this. However, it's not entirely clear what effect they are exactly studying. It seems that they investigate the effect of dams on the young water fraction (Fyw) and/or mean transit times (MTT). But it's not clear/not explained why this would be relevant. Why would the reader be interested in this? Somehow the authors make the relation with water resources management and/or studying the water circulation; however, this is not clear from the text. Thus I would strongly recommend to improve the justification of their study.
Secondly, it's not entirely clear what the novelty of the paper is. More scientists studied Fyw and MTT along rivers and the hypothesis (figure 6) is not new as this is coming from Song et al 2020 and Jodar et al 2016. Hence the manuscript would benefit from explaining the novelty.
In general, the paper is well written and it's easy to read and concise. However, I think more can be done with the result. In its current form, they only study the damping and Fyw and compare this for the disturbed and undisturbed catchment. But what about seasonal changes? And the effect of landuse (of the different subcatchments). Furthermore, the MTT is only given for the two catchments. Nothing is done with this information, nor an attempt is done to explain the differences. To me a large MTT for the larger catchment is not surprising.
To conclude, I think the paper can be a nice contribution but needs a major revision where they focus on the scope, novelty, and a more elaborative analysis. In the attachment more detailed comments can be found.
-
AC2: 'Reply on RC2', Guofeng Zhu, 26 Feb 2025
Author responses
Thank you very much for your E-mail of December 30th, 2024. We appreciate the editor and reviewer′s constructive comments and suggestions for our manuscript entitled “Dams extend the surface water renewal time in inland river basins: A comparative study based on stable isotope data from two different basin” with the reference HESS-2024-277
According to the reviewer's comments, we have revised our manuscript carefully. The revised portions have been marked in red in the manuscript track changes version. The main corrections and the response to the reviewer′s comments are as follows.
Responses to the reviewer’s comments
Response to Reviewer #2
- Clarity and Rigor of the Paper
Reviewer’s Comment:
The paper lacks sufficient explanation, making it difficult for readers to follow certain sections. Specifically, the technical background (e.g., L54-58) does not adequately discuss mean transit times (MTTs), and the definition of the young water fraction (Fyw) and its importance are not clearly stated.
Response and Revisions:
We have expanded the discussion of MTT and Fyw in the Introduction section. The following changes were made:
Discussion of MTT: In L54-58, we added a detailed explanation of MTT, its significance in hydrological studies, and references to McGuire and McDonnell (2006) and Hrachowitz et al. (2009), emphasizing the role of MTT in understanding catchment hydrological functions.
Definition and Importance of Fyw: In L60-65, we clarified the concept of Fyw and its application in non-stationary catchments, citing Kirchner (2016) and Jasechko et al. (2016) to highlight the unique advantages of Fyw in assessing hydrological responses.2. Secondly, it's not entirely clear what the novelty of the paper is. More scientists studied Fyw and MTT along rivers and the hypothesis (figure 6) is not new as this is coming from Song et al 2020 and Jodar et al 2016. Hence the manuscript would benefit from explaining the novelty.
Thank you for your comment regarding the novelty of our paper. We appreciate the opportunity to clarify the unique contributions of our research and distinguish it from existing studies.
Reviewer’s Comment:
The statement “There are a number of factors influencing water transit times” (L66) requires further elaboration.
Response and Revisions:
In L66-70, we elaborated on the key factors influencing water transit times, including natural factors (e.g., vegetation cover, catchment area) and anthropogenic factors (e.g., dam construction), citing Cartwright et al. (2020) and Weiler et al. (2003) to discuss how these factors impact MTTs.
- Detail and Rigor of the Methods
Reviewer’s Comment:
The Methods section is too brief, particularly regarding the lumped parameter models (e.g., the gamma model).
Response and Revisions:
We have expanded Section 3.2 to include a detailed description of the gamma model, its mathematical formulation, parameter selection, and its application in hydrological studies. The following changes were made:
Parameter Selection for the Gamma Model: In L155-160, we explained the significance of the α and β parameters and their influence on transit time distributions, citing Stewart et al. (2017) to justify our parameter choices.
Model Uncertainties: In L165-170, we discussed potential issues with the gamma model, such as aggregation and truncation effects, and referenced Kirchner (2016) and Stewart et al. (2010) to explain how Fyw was used to constrain MTT estimates.
- Discussion and Interpretation of Results
Reviewer’s Comment:
The Results section lacks in-depth discussion and fails to highlight the novelty and international significance of the study.
Response and Revisions:
We have expanded Section 5 to include a detailed discussion of the results, particularly the impact of dams on water transit times and the international context of the study. The following changes were made:
Impact of Dams on Water Transit Times: In L260-270, we compared our findings with global studies (e.g., Lehner et al., 2011; Zarfl et al., 2015) to discuss how dams prolong water transit times through interception and evaporation, emphasizing the unique contribution of this study in arid inland river basins.
Novelty of the Study: In L330-340, we highlighted that this study is the first to quantitatively assess the impact of dams on water cycle times from an isotope dynamics perspective and discussed its potential applications in global water cycle research.
- Discussion of Uncertainties
Reviewer’s Comment:
The discussion of uncertainties is incomplete, particularly regarding the derivation of the input function and the impact of varying model parameters.
Response and Revisions:
We have expanded Section 5.3 to include a detailed analysis of uncertainties. The following changes were made:
Uncertainties in the Input Function: In L305-310, we discussed the influence of seasonal variations in precipitation isotope data on Fyw and MTT estimates, citing Stockinger et al. (2016) to emphasize the importance of high sampling frequency in improving result accuracy.
Uncertainties in Model Parameters: In L315-320, we analyzed the impact of varying α and β parameters on MTT estimates and referenced Hrachowitz et al. (2011) to explain how the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to quantify model uncertainties.
- International Context and Significance of the Study
Reviewer’s Comment:
The conclusion that dams prolong water transit times is unsurprising, and the study lacks sufficient comparison with other research.
Response and Revisions:
We have expanded Section 6 to include a discussion of the international context of the study. The following changes were made:
Comparison with Other Studies: In L345-355, we compared our findings with global research (e.g., Vörösmarty et al., 1997; Wang et al., 2019) to highlight the similarities and differences, emphasizing the unique contribution of this study in arid inland river basins.
Significance of the Study: In L360-370, we discussed the potential implications of this study for global water cycle research, particularly in guiding water resource management in arid regions.
Through these revisions, we have significantly improved the clarity, rigor, and academic value of the manuscript. We believe these changes align the paper with the publication standards of major international journals and provide new insights into global water cycle research. Once again, we sincerely appreciate your constructive feedback and look forward to your further comments.
Best regards,
The Authors
Citation: https://doi.org/10.5194/hess-2024-277-AC2
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AC2: 'Reply on RC2', Guofeng Zhu, 26 Feb 2025
Status: closed
-
RC1: 'Comment on hess-2024-277', Anonymous Referee #1, 19 Nov 2024
This is potentially an interesting study but, as written, this paper falls short of what is required for publication in a major international journal such as HESS. I have provided several general comments but have not gone through some of the sections (the results or regional setting) in detail as the basis of the paper needs serious attention. In its current form, presenting results with little discussion or explanation (and not outlining what is novel) is unlikely to create interest with a broad international readership. I understand that getting negative results is never pleasant, but I hope that these comments help in revising the study.
Here are the general issues with the paper.
Firstly, there is a general lack of explanation such that the reader cannot easily follow aspects of the text . The paper is relatively short; however, the brevity has been achieved at the expense of clarity and rigor. For example, lines 51-75 present the general the technical background and this section needs to convey to the reader the important background and identify knowledge gaps, problems, or contrasting approaches. However, it falls short of this, for example:
1) L54-58. Some broader discussion of mean transit times and the issues around these would be useful.
2) Likewise, you should define what the young water fraction is and why it is important. The approach of determining Fwy rather than a mean transit time is due to flow systems not being stationary (which is an assumption in much of the early work using tracers such as stable isotopes to determine MTTs). This is well discussed in Kirchner (2016) and Jasechko et al. (2016), both of which you cite.
3) Statements such as: “There are a number of factors influencing the water transit times” (L66) need explaining – what are they and how do they impact MTTs?
4) The Methods (Section 3) are also brief and a bit more detail on lumped parameter models (especially the gamma model, which is the one that you choose) is also needed.
Secondly, the calculations need to be more rigorous and thought through more. The basic outline of the calculations is presented in Section 3.2 and Section 5 presents the calculated results. However, nowhere is there any real discission of the results. Specifically:
5) You choose to estimate MTTs as well as Fwy but part of the reason for using Fwy is due to the stationarity problem that was identified by Kirchner (2016). Briefly that is that the assumption made when using LPMs with seasonal tracers that the flow system does not change over the year such the MTT is constant at all flows. However, the reality is that catchments discharge younger water during wetter conditions and older water during dry periods. Studies using tracers such as tritium (e.g. Cartwright et al., 2020, which you cite) and studies using other techniques such as flux tracking (e.g. Hrachowit et al., 2013. Hydrology and Earth System Sciences, 17, 533–564. https://doi.org/10.5194/hess-17-533-2013) or StorAge solutions (Benettin et al., 2015 Water Resources Research, 51, 9256–9272. https://doi.org/10.1002/2014WR016600) also show this. Given that this issue is implicitly recognised, is it really valid to calculate MTTs using a lumped parameter model?
6) If you do use a lumped parameter model, you need to discuss some of the associated potential problems, such as:
- Aggregation (i.e. macroscopic mixing from different sources); this is discussed in Kirchner (2016, Hydrol. Earth Syst. Sci., 20, 279–297, https://doi.org/10.5194/hess-20-279-2016).
- Truncation, which is the possibility that there is older water with an attenuated signal, such that the MTTs are underestimated (e.g. Stewart, et al., 2010, Hydrol. Process. 24, 1646–1659. https://doi.org/10.1002/hyp.7576). Given the longest MTTs you estimate are >9 years, this is likely to be a significant issue.
7) What are the parameters in the gamma model and why where they chosen? The transit time distributions in this model vary with the alpha parameter (e.g. Stewart et al., 2017. Hydrol. Earth Syst. Sci., 21, 4615–4627, https://doi.org/10.5194/hess-21-4615-2017 ) and the calculated MTT also varies. It looks like you have used only a single parameterisation but there are not details of which one and why it was chosen. Is there any advantage of using the gamma model over say the exponential or exponential-piston flow lumped parameter models or the dispersion model (which like the gamma model is fairly generic)
8) Uncertainties are discussed (Sections 5.1 and 5.3), but it is not always clear what was taken into account. Statements such as “As the spatial and temporal heterogeneity of the basin may cause errors in the MTT estimates, we used Fyw to constrain the estimated MTT results” are not very clear. There are several uncertainties that should be included, such as:
- Uncertainties arising from the derivation of the input function. Figure 3 shows that there is a decent sinusoidal variation in the precipitation isotopes, and that the fitted curve is reasonable but there will still be an uncertainty here that translates into errors in Fyw and MTTs
- The impacts of varying the parameters in the lumped parameter models
- Aggregation and truncation
The papers that you cite plus the ones also referred to here have a far higher lever of rigor than you have attempted and the results come across as being far more convincing.
Finally, I am not convinced about the importance and novelty of the study.
- Concluding that water transit times in dammed catchments are longer would seem unsurprising (the reservoirs behind the dams have a storage time that is longer than the storage time in a free-flowing river after all). So, what is the new understanding here?
- Are there other studies with which you can compare this work (which would place it in a better international context)? If it is the first such study, then discuss that and perhaps do more justification that the calculations can apply to heavily modified rivers that are more susceptible to evaporation which obviously modifies the stable isotopes.
Citation: https://doi.org/10.5194/hess-2024-277-RC1 -
AC1: 'Reply on RC1', Guofeng Zhu, 26 Feb 2025
Author responses
Thank you very much for your E-mail of December 30th, 2024. We appreciate the editor and reviewer′s constructive comments and suggestions for our manuscript entitled “Dams extend the surface water renewal time in inland river basins: A comparative study based on stable isotope data from two different basin” with the reference HESS-2024-277
According to the reviewer's comments, we have revised our manuscript carefully. The revised portions have been marked in red in the manuscript track changes version. The main corrections and the response to the reviewer′s comments are as follows.
Responses to the reviewer’s comments
Response to Reviewer #1
- Clarity and Rigor of the Paper
Reviewer’s Comment:
The paper lacks sufficient explanation, making it difficult for readers to follow certain sections. Specifically, the technical background (e.g., L54-58) does not adequately discuss mean transit times (MTTs), and the definition of the young water fraction (Fyw) and its importance are not clearly stated.
Response and Revisions:
We have expanded the discussion of MTT and Fyw in the Introduction section. The following changes were made:
Discussion of MTT: In L54-58, we added a detailed explanation of MTT, its significance in hydrological studies, and references to McGuire and McDonnell (2006) and Hrachowitz et al. (2009), emphasizing the role of MTT in understanding catchment hydrological functions.
Definition and Importance of Fyw: In L60-65, we clarified the concept of Fyw and its application in non-stationary catchments, citing Kirchner (2016) and Jasechko et al. (2016) to highlight the unique advantages of Fyw in assessing hydrological responses.
Reviewer’s Comment:
The statement “There are a number of factors influencing water transit times” (L66) requires further elaboration.
Response and Revisions:
In L66-70, we elaborated on the key factors influencing water transit times, including natural factors (e.g., vegetation cover, catchment area) and anthropogenic factors (e.g., dam construction), citing Cartwright et al. (2020) and Weiler et al. (2003) to discuss how these factors impact MTTs.
- Detail and Rigor of the Methods
Reviewer’s Comment:
The Methods section is too brief, particularly regarding the lumped parameter models (e.g., the gamma model).
Response and Revisions:
We have expanded Section 3.2 to include a detailed description of the gamma model, its mathematical formulation, parameter selection, and its application in hydrological studies. The following changes were made:
Parameter Selection for the Gamma Model: In L155-160, we explained the significance of the α and β parameters and their influence on transit time distributions, citing Stewart et al. (2017) to justify our parameter choices.
Model Uncertainties: In L165-170, we discussed potential issues with the gamma model, such as aggregation and truncation effects, and referenced Kirchner (2016) and Stewart et al. (2010) to explain how Fyw was used to constrain MTT estimates.
- Discussion and Interpretation of Results
Reviewer’s Comment:
The Results section lacks in-depth discussion and fails to highlight the novelty and international significance of the study.
Response and Revisions:
We have expanded Section 5 to include a detailed discussion of the results, particularly the impact of dams on water transit times and the international context of the study. The following changes were made:
Impact of Dams on Water Transit Times: In L260-270, we compared our findings with global studies (e.g., Lehner et al., 2011; Zarfl et al., 2015) to discuss how dams prolong water transit times through interception and evaporation, emphasizing the unique contribution of this study in arid inland river basins.
Novelty of the Study: In L330-340, we highlighted that this study is the first to quantitatively assess the impact of dams on water cycle times from an isotope dynamics perspective and discussed its potential applications in global water cycle research.
- Discussion of Uncertainties
Reviewer’s Comment:
The discussion of uncertainties is incomplete, particularly regarding the derivation of the input function and the impact of varying model parameters.
Response and Revisions:
We have expanded Section 5.3 to include a detailed analysis of uncertainties. The following changes were made:
Uncertainties in the Input Function: In L305-310, we discussed the influence of seasonal variations in precipitation isotope data on Fyw and MTT estimates, citing Stockinger et al. (2016) to emphasize the importance of high sampling frequency in improving result accuracy.
Uncertainties in Model Parameters: In L315-320, we analyzed the impact of varying α and β parameters on MTT estimates and referenced Hrachowitz et al. (2011) to explain how the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to quantify model uncertainties.
- International Context and Significance of the Study
Reviewer’s Comment:
The conclusion that dams prolong water transit times is unsurprising, and the study lacks sufficient comparison with other research.
Response and Revisions:
We have expanded Section 6 to include a discussion of the international context of the study. The following changes were made:
Comparison with Other Studies: In L345-355, we compared our findings with global research (e.g., Vörösmarty et al., 1997; Wang et al., 2019) to highlight the similarities and differences, emphasizing the unique contribution of this study in arid inland river basins.
Significance of the Study: In L360-370, we discussed the potential implications of this study for global water cycle research, particularly in guiding water resource management in arid regions.
Citation: https://doi.org/10.5194/hess-2024-277-AC1
-
RC2: 'Comment on hess-2024-277', Anonymous Referee #2, 29 Dec 2024
The authors try to investigate the effects of dams and are using stable water isotopes to achieve this. However, it's not entirely clear what effect they are exactly studying. It seems that they investigate the effect of dams on the young water fraction (Fyw) and/or mean transit times (MTT). But it's not clear/not explained why this would be relevant. Why would the reader be interested in this? Somehow the authors make the relation with water resources management and/or studying the water circulation; however, this is not clear from the text. Thus I would strongly recommend to improve the justification of their study.
Secondly, it's not entirely clear what the novelty of the paper is. More scientists studied Fyw and MTT along rivers and the hypothesis (figure 6) is not new as this is coming from Song et al 2020 and Jodar et al 2016. Hence the manuscript would benefit from explaining the novelty.
In general, the paper is well written and it's easy to read and concise. However, I think more can be done with the result. In its current form, they only study the damping and Fyw and compare this for the disturbed and undisturbed catchment. But what about seasonal changes? And the effect of landuse (of the different subcatchments). Furthermore, the MTT is only given for the two catchments. Nothing is done with this information, nor an attempt is done to explain the differences. To me a large MTT for the larger catchment is not surprising.
To conclude, I think the paper can be a nice contribution but needs a major revision where they focus on the scope, novelty, and a more elaborative analysis. In the attachment more detailed comments can be found.
-
AC2: 'Reply on RC2', Guofeng Zhu, 26 Feb 2025
Author responses
Thank you very much for your E-mail of December 30th, 2024. We appreciate the editor and reviewer′s constructive comments and suggestions for our manuscript entitled “Dams extend the surface water renewal time in inland river basins: A comparative study based on stable isotope data from two different basin” with the reference HESS-2024-277
According to the reviewer's comments, we have revised our manuscript carefully. The revised portions have been marked in red in the manuscript track changes version. The main corrections and the response to the reviewer′s comments are as follows.
Responses to the reviewer’s comments
Response to Reviewer #2
- Clarity and Rigor of the Paper
Reviewer’s Comment:
The paper lacks sufficient explanation, making it difficult for readers to follow certain sections. Specifically, the technical background (e.g., L54-58) does not adequately discuss mean transit times (MTTs), and the definition of the young water fraction (Fyw) and its importance are not clearly stated.
Response and Revisions:
We have expanded the discussion of MTT and Fyw in the Introduction section. The following changes were made:
Discussion of MTT: In L54-58, we added a detailed explanation of MTT, its significance in hydrological studies, and references to McGuire and McDonnell (2006) and Hrachowitz et al. (2009), emphasizing the role of MTT in understanding catchment hydrological functions.
Definition and Importance of Fyw: In L60-65, we clarified the concept of Fyw and its application in non-stationary catchments, citing Kirchner (2016) and Jasechko et al. (2016) to highlight the unique advantages of Fyw in assessing hydrological responses.2. Secondly, it's not entirely clear what the novelty of the paper is. More scientists studied Fyw and MTT along rivers and the hypothesis (figure 6) is not new as this is coming from Song et al 2020 and Jodar et al 2016. Hence the manuscript would benefit from explaining the novelty.
Thank you for your comment regarding the novelty of our paper. We appreciate the opportunity to clarify the unique contributions of our research and distinguish it from existing studies.
Reviewer’s Comment:
The statement “There are a number of factors influencing water transit times” (L66) requires further elaboration.
Response and Revisions:
In L66-70, we elaborated on the key factors influencing water transit times, including natural factors (e.g., vegetation cover, catchment area) and anthropogenic factors (e.g., dam construction), citing Cartwright et al. (2020) and Weiler et al. (2003) to discuss how these factors impact MTTs.
- Detail and Rigor of the Methods
Reviewer’s Comment:
The Methods section is too brief, particularly regarding the lumped parameter models (e.g., the gamma model).
Response and Revisions:
We have expanded Section 3.2 to include a detailed description of the gamma model, its mathematical formulation, parameter selection, and its application in hydrological studies. The following changes were made:
Parameter Selection for the Gamma Model: In L155-160, we explained the significance of the α and β parameters and their influence on transit time distributions, citing Stewart et al. (2017) to justify our parameter choices.
Model Uncertainties: In L165-170, we discussed potential issues with the gamma model, such as aggregation and truncation effects, and referenced Kirchner (2016) and Stewart et al. (2010) to explain how Fyw was used to constrain MTT estimates.
- Discussion and Interpretation of Results
Reviewer’s Comment:
The Results section lacks in-depth discussion and fails to highlight the novelty and international significance of the study.
Response and Revisions:
We have expanded Section 5 to include a detailed discussion of the results, particularly the impact of dams on water transit times and the international context of the study. The following changes were made:
Impact of Dams on Water Transit Times: In L260-270, we compared our findings with global studies (e.g., Lehner et al., 2011; Zarfl et al., 2015) to discuss how dams prolong water transit times through interception and evaporation, emphasizing the unique contribution of this study in arid inland river basins.
Novelty of the Study: In L330-340, we highlighted that this study is the first to quantitatively assess the impact of dams on water cycle times from an isotope dynamics perspective and discussed its potential applications in global water cycle research.
- Discussion of Uncertainties
Reviewer’s Comment:
The discussion of uncertainties is incomplete, particularly regarding the derivation of the input function and the impact of varying model parameters.
Response and Revisions:
We have expanded Section 5.3 to include a detailed analysis of uncertainties. The following changes were made:
Uncertainties in the Input Function: In L305-310, we discussed the influence of seasonal variations in precipitation isotope data on Fyw and MTT estimates, citing Stockinger et al. (2016) to emphasize the importance of high sampling frequency in improving result accuracy.
Uncertainties in Model Parameters: In L315-320, we analyzed the impact of varying α and β parameters on MTT estimates and referenced Hrachowitz et al. (2011) to explain how the Generalized Likelihood Uncertainty Estimation (GLUE) method was used to quantify model uncertainties.
- International Context and Significance of the Study
Reviewer’s Comment:
The conclusion that dams prolong water transit times is unsurprising, and the study lacks sufficient comparison with other research.
Response and Revisions:
We have expanded Section 6 to include a discussion of the international context of the study. The following changes were made:
Comparison with Other Studies: In L345-355, we compared our findings with global research (e.g., Vörösmarty et al., 1997; Wang et al., 2019) to highlight the similarities and differences, emphasizing the unique contribution of this study in arid inland river basins.
Significance of the Study: In L360-370, we discussed the potential implications of this study for global water cycle research, particularly in guiding water resource management in arid regions.
Through these revisions, we have significantly improved the clarity, rigor, and academic value of the manuscript. We believe these changes align the paper with the publication standards of major international journals and provide new insights into global water cycle research. Once again, we sincerely appreciate your constructive feedback and look forward to your further comments.
Best regards,
The Authors
Citation: https://doi.org/10.5194/hess-2024-277-AC2
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AC2: 'Reply on RC2', Guofeng Zhu, 26 Feb 2025
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