Predicting hydrologic responses to climate changes in highly glacierized and mountainous region Upper Indus Basin

The Upper Indus Basin (UIB) is a major source of supplying water to different areas because of snow and glaciers melt and is also enduring the regional impacts of global climate change. The expected changes in temperature, precipitation and snowmelt could be reasons for further escalation of the problem. Therefore, estimation of hydrological processes is critical for UIB. The objectives of this paper were to estimate the impacts of climate change on water resources and future projection for surface water under different climatic scenarios using soil and water assessment tool (SWAT). The methodology includes: (i) development of SWAT model using land cover, soil and meteorological data; (ii) calibration of the model using daily flow data from 1978 to 1993; (iii) model validation for the time 1994–2003; (iv) bias correction of regional climate model (RCM), and (v) utilization of bias-corrected RCM for future assessment under representative concentration pathways RCP4.5 and RCP8.5 for mid (2041–2070) and late century (2071–2100). The results of the study revealed a strong correlation between simulated and observed flow with R2 and Nash–Sutcliff efficiency (NSE) equal to 0.85 each for daily flow. For validation, R2 and NSE were found to be 0.84 and 0.80, respectively. Compared to baseline period (1976–2005), the result of RCM showed an increase in temperature ranging from 2.36°C to 3.50°C and 2.92°C to 5.23°C for RCP4.5 and RCP8.5 respectively, till the end of the twenty-first century. Likewise, the increase in annual average precipitation is 2.4% to 2.5% and 6.0% to 4.6% (mid to late century) under RCP4.5 and RCP8.5, respectively. The model simulation results for RCP4.5 showed increase in flow by 19.24% and 16.78% for mid and late century, respectively. For RCP8.5, the increase in flow is 20.13% and 15.86% during mid and late century, respectively. The model was more sensitive towards available moisture and snowmelt parameters. Thus, SWAT model could be used as effective tool for climate change valuation and for sustainable management of water resources in future.

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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. Thank you for submitting "redicting Hydrologic Responses to Climate Change in Highly Glacierized and Mountainous Region Upper Indus Basin" to Royal Society Open Science. I have received two reviews of your manuscript, which are included below and/or attached. Both reviews indicate that this is an interesting and generally well implemented modelling study; however, one reviewer highlights several areas that require further attention. My own views on the paper are well-aligned with this review.
While I suggest that you address each of the comments indicated in the review, a greater description of the treatment of glacier melt and further discussion of the findings (especially in reference to previous work in the Indus basin) is especially important.
I am therefore returning the paper to you so that you can make the necessary changes, which fall under the category of 'Major Revisions'.
Author's Response to Decision Letter for (RSOS-191957.R0) Decision letter (RSOS-191957.R1) We hope you are keeping well at this difficult and unusual time. We continue to value your support of the journal in these challenging circumstances. If Royal Society Open Science can assist you at all, please don't hesitate to let us know at the email address below.
Dear Dr Akbar: On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-191957.R1 entitled "Predicting hydrologic responses to climate changes in highly glacierized and mountainous region Upper Indus Basin" has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the Editor suggestions.
The Editors have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
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• Data accessibility It is a condition of publication that all supporting data are made available either as supplementary information or preferably in a suitable permanent repository. The data accessibility section should state where the article's supporting data can be accessed. This section should also include details, where possible of where to access other relevant research materials such as statistical tools, protocols, software etc can be accessed. If the data has been deposited in an external repository this section should list the database, accession number and link to the DOI for all data from the article that has been made publicly available. Data sets that have been deposited in an external repository and have a DOI should also be appropriately cited in the manuscript and included in the reference list.
If you wish to submit your supporting data or code to Dryad (http://datadryad.org/), or modify your current submission to dryad, please use the following link: http://datadryad.org/submit?journalID=RSOS&manu=RSOS-191957.R1 • Competing interests Please declare any financial or non-financial competing interests, or state that you have no competing interests.
• Authors' contributions All submissions, other than those with a single author, must include an Authors' Contributions section which individually lists the specific contribution of each author. The list of Authors should meet all of the following criteria; 1) substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; and 3) final approval of the version to be published.
All contributors who do not meet all of these criteria should be included in the acknowledgements.
We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. Dear Muhammad Shah and co-authors, My apologies for the delay in returning these comments to you. As already communicated, we had problems in seeking a sufficient number of referee reports, no doubt at least in part a consequence of the current global pandemic. Many thanks for providing a rebuttal to the major corrections suggested by the first original reviewer. I have now assessed these myself. Overall, these have improved the clarity and flow of the manuscript and helped place the study more clearly alongside existing research o9n the topic. I have the following comments, based on the original 'major changed' suggested: 1) The introduction and discussion now provide greater context and links with existing literature. The comparison with other work (P14) is especially informative. As a minor addition, I think it would be useful to include a sentence towards the end of section 1, indicating clearly how this study builds upon those existing studies cited. Essentially, a clear statement of novelty would be useful here.
2) Details of the methods applied are now much clearer (though see my comment below). Justifications for research choices (e.g. choice of RCM) are now provided and the precedents for these research methods stated explicitly, which is good to see. 3) I think there remains a need for greater clarity around the representation of glaciers in the model. The reviewer rightly highlighted this as a point requiring further description, given the expected significance of glacier melt in the future hydrology of the study basin. The reviewer questioned a number of times whether or not the glaciers are represented dynamically in the model, and I remain unsure of the answer even having read through the new corrections. I think this point needs to be addressed prior to publication. 4) All minor comments have been addressed. 5) The writing is clear and understandable throughout, but certainly a final proof read is required. This most likely comes at a later stage in the publication process, but I thought it best to raise as a note here. Based on the above, I suggest that only minor changes are needed before this paper should be published in RSOS. These should not be too onerous and do not require any new data analysis. with other studies (that may have used a more dynamic treatment of glaciers?) would be useful. Perhaps even a conceptual flow chart as to how glacier response is incorporated would be useful. I see this as the main outstanding issue here, but should be relatively easy to address.
Associate Editor: 2 Comments to the Author: Many thanks for revising the manuscript as detailed. Given the nature of the changes and addition of whole sections of text, I feel it appropriate to send this out to review.

Decision letter (RSOS-191957.R2)
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Dear Dr Akbar, It is a pleasure to accept your manuscript entitled "Predicting hydrologic responses to climate changes in highly glacierized and mountainous region Upper Indus Basin" in its current form for publication in Royal Society Open Science.
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Review of Predicting Hydrologic Responses to Climate Change in Highly Glacierized and Mountainous Region Upper Indus Basin by Shah et al.
This manuscript documents an application of climate downscaling to upper Indus basin. The problem setup is generally Ok, but writing needs to be significant improved. Currently there are many typos and grammar errors. I only give several examples below P3, L15, "…severe storms and floods have been occurred in its history" should be "severe storms and floods have occurred in its history" P3, L16-17, "Besides, the swift population growth and the accompanying land-use alterations further intensifying the problems induced by climate-change …" should be "Besides, the rapid population growth and the accompanying land-use alterations further intensify the problems induced by climatechange" P4, L10-L11, "The River Indus can be classifies as one of the major river in Asia,…" => "The Indus River can be classified as one of the major rivers in Asia,"

Predicting Hydrologic Responses to ClimateChange in Highly Glacierized and Mountainous Region Upper Indus Basin
Muhammad Izhar Shah, Asif Khan, Tahir Ali Akbar, Quazi K Hassan,Asim Jahangir Khanand Ashraf Dewan The paper looked at the impact of climate change on river flows in the Upper Indus basin using SWAT hydrological model which was forced with high resolution regional climate model (RCMs) for two future scenarios RCP4.5 and 8.5. The model has able to replicate the historic reference period well, based on which the future hydrology is quantified. Under different scenarios, the future flows are likely to increase.   The change in precipitation under RCP8.5 from mid to late century is from 6% to 4.6% in abstract. However, in conclusion, the reverse has been written. It should be corrected before publishing.

Predicting hydrologic responses to climate changes in highly glacierized and mountainous region Upper Indus Basin
The paper looked at the impact of climate change on river flows in the Upper Indus basin using SWAT hydrological model which was forced with high resolution regional climate model (RCMs) for two future scenarios RCP4.5 and 8.5. The model has able to replicate the historic reference period well, based on which the future hydrology is quantified. Under different scenarios, the future flows are likely to increase.

Response:
The authors would like to appreciate the reviewers' time and effort for providing us her/his valuable comments.

Comment 1:
The

Response:
Yes, all of the mentioned and some other important papers have been cited in introduction and discussion section (please see in Pages 2 and 14).

Comment 2:
I think it would be very useful if authors compare the results with these published results to see where the historical hydrological modelling from this study compares

Response:
Yes, the above information has been added and comparison is drawn in discussion section (please see Page 14).

Response:
To incorporate the contribution of snow/glacier melt in the model, we used Temperature Index approach [1] with elevation bands. This approach allows the model to replicate the response of snow/glacier in a glaciated watershed by distributing the sub basins to several elevation bands. SWAT model provides melt water at each sub basin including the contribution of melt water from both snow and glaciers [2]. SFTMP, SMTMP, SMFMN, SMFMX, TIMP, SNO50COV and SNOCOVMX are some parameters used by SWAT model for melt contribution form snow/glaciers. In SWAT model, the glacier melt can be accounted using snowmelt parameters such as depletion curves and temperature lag factor. All these parameters were successfully incorporated into the model and the information about the parameters were collected from literature study. Furthermore, detailed information can be found in Neitsch et al., [3].
The above information has been added (please see Section 3.1, Page 7).

Comment 4:
The methodology of using one RCM from CORDEX is not strong methodology, as the bias within one model could be high. There are many studies which look at the ensemble approach of few models.

Response:
There are many research studies that considered several GCMs or RCMs. But in a study, conducted by Khan and Koch, 2018 [4], a step-wise methodology was adopted for shortlisting and selection of suitable climate models for the Upper Indus Basin, based on a range of projected mean and extreme changes and skill in reproducing the past climate. The study was concentrated on RCA4 regional climate models from CORDEX. Out of all the selected CORDEX-South Asia experiments, the RCM "NorESM1-M_RCA4" was the most appropriate as depiction of the median tendencies of future climate for UIB. Hence, the NorESM1-M_RCA4 was selected for the present study.
Description of the RCM used in this study Rossby Centre regional atmospheric model version 4 (RCA4) [5] The above information has been added (please see Section 2.2.4, Page 6).

Comment 5:
The increase in future flow is attributed to what? Increase in rainfall or increase in accelerated melting from glacier. It is not clear how the future temperature has affected glacier response. Is the SWAT glacier incorporation (if yes) is dynamic (changes in glacier area in the future) and stagnant?

Response:
Based on our results, a projected change in temperature varies between 2.36°C to 3.5°C under RCP4.5 (from mid-century to late century) and 2.92°C to 5.23°C under RCP8.5 (from mid-century to late century) was observed. Similarly, the expected changes in precipitation ranges from 2.4% to 2.5% for RCP4.5 and 6% to 4.6% under RCP8.5 (from mid-century to late century). It is clear that the increase in the future flows may be attributed to the increased temperature and also the precipitation extremes.
In the Upper Indus Basin, the increased temperature contributed to increased melt rates which rises the streamflow [6]. The same results were reported by Garee, K. et al., [7] that annual flow will increase ranging from 7.57% to 32.12% till the end of 21 st century with a temperature increase from 1.39°C to 6.58°C. In our study, the flow increases in both mid (2041-2070) as well as in late century (2071-2100). The increased flow is due to high melt rates and the algorithm of snow/glacier melt was successfully incorporated in the SWAT model in the form of temperature index [1] with elevation bands. The SWAT model allows the sub basins to further split into ten elevation bands and the snow/glacier melt processes are simulated individually. The snow melt parameters (SMFMX, SMFMN), temperature lag factor (TIMP), snow fall temperature (SFTMP) and snow melt temperature (SMTMP) are allowed to vary spatially within the sub basins.
The above information has been added (please see Section 5, i.e., discussion, Page 14).

Comment 6:
It is not clear how the authors have implemented glacier melt in the SWAT model. Authors have used the snow/glacier melt but it is not clear whether snow and glacier melt are deal in a different way, as both have different melt processes; snow is more seasonal and based on available snow storage, but glacier remains available even the snow is gone.

Response:
Yes the snow and glacier are different melt processes. In the current study, the temperature index approach [1] with elevation band is used to simulate the snow/glacier melt and its contribution to streamflow. SWAT model provides melt water at each sub basin including the contribution from both snow and glaciers. The glacier melt in SWAT can be accounted using snowmelt parameters such as depletion curves and temperature lag factor. All these parameters were used in the model. Similarly, the temperature index approach has been used by babur et al., [8] in Jhelum river basin, Garee et al., [7] in Hunza river basin, Anjum et al., [9] in swat river basin and zhang et al., [10] in yellow river basin for streamflow simulation in glaciated watershed.
The above information has been added (please see Section 3.1, Page 7).

Response:
In our study, the snow and glacier melt processes are dealt with the help of temperature index combined [1] with elevation band approach. The above mentioned authors used different models in their studies. In the present study, we used the Soil & Water Assessment Tool (SWAT) which is a river basin scale model developed to quantify the effect of land management practices in large and complex watersheds. In SWAT model, there are some parameters related to and most sensitive to glacier and snowmelt i.e. SFTMP, SMTMP, SMFMN, SMFMX, TIMP, SNO50COV and SNOCOVMX. The SFTMP (snowfall temperature) is used as a threshold to categorize the precipitation as rainfall or snowfall. When the air temperature is lower than SFTMP, the precipitation is classified as snowfall [2]. The snowpack will not melt until the snowpack temperature exceeds the threshold value i.e. SMTMP (snowmelt base temperature). SMFMX is the melt factor for 21 June and SMFMN is the melt factor for 21 December [2]. SNOCOVMX represents the snow water content agreeing with watershed full snow cover [7,11]. The SNO50COV parameter which is volume of snow water that relates to 50% snow cover, can be used to adjust shape of depletion curve [12]. The TIMP is an empirical parameter used for snow density, extent, depth and other factors affecting snow pack temperature [11]. TIPM is used to regulate temperature effect on previous days based on current temperature of snow pack.
The above information has been added (please see Section 4.1, Pages 10 and 11).

Comment 8:
What is the basis for lapse rate approach of this research? It would be better if you provide reference of the approach.

Response:
One of the co-author, Asim Jahangir Khan [13] used a new method for interpolation and correction of the data (lapse rate approach) across the whole Upper Indus Basin considering the orographic effect in the region and specifically correcting the influences induced by higher elevation, glacier mass-balance and actual evapotranspiration. In the present study, we used the same lapse rate approach.