The Role of Large Dams in a Transboundary Drought Management Co-Operation Framework—Case Study of the Kabul River Basin

Round 1

Reviewer 1 Report

The manuscript focused on the role of future reservoirs in migrating hydrological drought in a transboundary river basin. The major problems of the study include:

1. The scientific significance and scientific background are not clearly described in the Introduction Section, whether the focus is the impacts of dams on hydrological drought, or transboundary drought management?
2. Data are mot well described. It says on Line 208-209: “The scattered, measured data from ten flow stations in KRB for 2007 to 2015 were organized’. A more detailed description is needed. What’s the spatial resolution of CFSR data It says “simulated and available measured climate data showed a 210 close relationship with an average determination coefficient of 0.71 for precipitation and 0.76 211 for the temperature at the ten climate stations“, where and when are the climate data measured? In addition, data about reservoir and irrigation are missing. When the author says : “Since most studies predict up to 25% irrigated land increase in KRB, we have increased the World Bank proposed irrigated land by another 30% to account for unplanned agricultural land expansion, making it 77,129 ha irrigated land”, there is no citation about “most studies”, and why should the “unplanned agricultural land expansion” be considered?
3. The methodology should be reorganized. The part on Line 138 – Line 192 about SSI calculation should be concise. How low frequency is conducted, how dam operation is simulated, and how the effects about irrigation is simulated should be presented.
4. According to the title of the paper, i.e., "The Role of Large Dams in a Transboundary Drought Management Co-operation Framework", the paper should present the "Co-operation Framework" first, then show how dams are operated under such a framework. But in fact the framework is proposed at the end of the paper. The overall structure is not quite logical. And, it seems that the contents in section 3.5 about water rights and section 3.6 about drought management are too conceptual, not well connected with the analyses and results by model simulation.

 

Some specific comments:

 

Line 33: ‘hydrological’ or “hydrologic” drought, the expression is not consistent in the manuscript.

Line 74-75: remove the remarks of literature.

Line 107, Figure 2 should focus on the case study region. Please revise the Figure 3, replace Figure 2 with the revised Figure 3, and clearly show the names (or the No. in Table 1) of locations of all dams.

Line 175: is the CDV the same with ADV in line 151 and ACDV in line 188? What does Qs mean in the formula?

Line 178: which one is the selected threshold in the manuscript, 70%, 80%, or 90%?

Line 234: please describe the hydraulic features of the future dams used in SWAT model and the set of future reservoir scenarios in detail.

Line 299: the subtitle needs revision, since water rights and drought management are not belonging to low flow assessment.

Line 394: the subtitle needs revision, as the authors focused on the drought status instead of the drought index. Some of the description of SSI (Standardized Streamflow Index) should be moved to methodology item.

Line 403: which timescale is the used in the manuscript.

Line 411: x-axis signature (Figure 7) should be translated into English.

Line 496-497: the meaning of “the 2075 - 2099 scenarios under RCP 4.5 and RCP 8.5 “ is not clear.

Author Response

Reviewer #1

1. The scientific significance and scientific background are not clearly described in the Introduction Section, whether the focus is the impacts of dams on hydrological drought, or transboundary drought management?

Authors’ Response: Thank you for this comment. In response, the Introduction Section has been significantly improved for clarity:

 

Line 71-75: “Although constructing new dams can resolve the low flow and hydrologic drought issue, environmental and social impacts brought by the dam construction should not be overlooked. In the latter part of this paper, a discussion of benefits and potential impacts of dam construction is provided.”

 

Line 86-91: “The main goal of this paper is to study the impacts of the climate change on the KRB flow regime and the potential benefits of the new reservoirs to retain water for the purposes of low flow augmentation. The issue of ‘steady’ flow to Pakistan from the Dakah outlet is a transboundary matter and the low flow has always been a matter of contention between the users of the two countries. These contentions and grievances are more visible during hydrologic drought events.”

 

2. Data are not well described. It says on Line 208-209: “The scattered, measured data from ten flow stations in KRB for 2007 to 2015 were organized’. A more detailed description is needed. What’s the spatial resolution of CFSR data It says “simulated and available measured climate data showed a 210 close relationship with an average determination coefficient of 0.71 for precipitation and 0.76 211 for the temperature at the ten climate stations“, where and when are the climate data measured? In addition, data about reservoir and irrigation are missing. When the author says : “Since most studies predict up to 25% irrigated land increase in KRB, we have increased the World Bank proposed irrigated land by another 30% to account for unplanned agricultural land expansion, making it 77,129 ha irrigated land”, there is no citation about “most studies”, and why should the “unplanned agricultural land expansion” be considered?

Authors’ Response: A more detailed description of the data has been added, including the spatial resolution of CFSR data, where and when the climate data measured, data about reservoir and irrigation, and citation about “most studies” in support of irrigated land. The reason for the 30% expansion of the irrigated land is to be conservative as in other similar studies we have noticed frequently there is economic pressure to irrigate more than originally planned to  obtain economic incentives and price of irrigated lands compared to barren lands.

 

A more detailed description of CFSR is provided in Line 249-254 as reads:

“Weather data including precipitation, temperature, solar radiation, wind speed, and relative air moisture from 1979 to 2014 were obtained from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) for the KRB. CFSR collects global, high-resolution climate data, coupled with atmosphere-ocean-land surface-sea ice system.

 

The Reservoir data are provided in Table 1. The Irrigation water demand data are provided in Table 2. New citations are added (Lines 233-227, 238, 276-285). And the reasoning for the 30% increase in agricultural land expansion is added in Lines: 310-313. “The agricultural land expansion is an unpredicted process in most developing countries. Studies by Sidiqi, 2018, Najmuddin, 2017, Qureshi, 2002, indicate an increase in agricultural land expansion beyond the predicted threshold in the KRB over the next 25 years.”

 

3. The methodology should be reorganized. The part on Line 138 – Line 192 about SSI calculation should be concise. How low frequency is conducted, how dam operation is simulated, and how the effects about irrigation is simulated should be presented.

Author’s Response: The SSI description was condensed. Please refer to lines 207-212:“Low frequency analysis is the probability of water availability in a specific location under a specific threshold which can qualify the low flow as hydrologic drought (Eris, et al. 2019). It provides information about the magnitude and frequency of flow discharges based on records of lowest annual discharges collected at stream gages. In this study the seven day average for two (Q_7,2), Five (Q_7,5), 10 (Q_7,10 ), 25 (Q_{7,25 )}, 50 (Q_7,50 ) and 100 (Q_7,100 ) return periods have been considered”

 

Line: 213-231: “Different scientific communities are using different types of distributions for flood and low flow (drought) frequency analysis. Great Britain and China use the generalized extreme value distribution and the lognormal distribution, respectively, while other countries commonly use other distributions such as log-Pearson and Gumbel (Singh and Strupczewski, 2002). The most popular distributions to conduct frequency analysis are Generalized Extreme Value (GEV), Weibull (W2), Gamma (G2), and Log-Normal with two parameters probability distribution functions (LN2), Weibull (W3), Gamma (G3) and Log-Normal with three parameters probability distribution functions (LN3). Additional studies carried out to evaluate the suitability of selecting distributional alternatives for flood frequency analysis are reported by Cunnane (1989), Hosking, & Wallis (1988), Nathan & Weinmann (1991), Chowdhury et al. (1991), Mkhand (2009) and Vogel et al. (1993). Given the findings reported from the World Meteorological Organization (WMO) (1989) wherein a survey was conducted and concluded that Lognormal distribution is one of the widely used distributions for flood frequency analysis (Bobee et al., 1993), hence was selected for flood frequency analysis.”  

 

Dam Operation: the Manuscript text was revised as (Line 441-445):

“The proposed reservoir operations procedures were assumed based on the monthly reservoir operation targets. The reservoir routing in the SWAT model was conducted based on the storage assigned for different months in flood and non-flood seasons. The reservoir water release was also synchronised in the model based on the monthly water demand as per the WB, 2010 report.” 

 

Effects irrigation on SWAT modelling: the Manuscript was revised as (Line 296-318)

“Over 80% of the KRB irrigation is conducted with surface water resources.

The study assumed the irrigated land expansion based on the WB reports and past trends. The study considered a 35%, 50% and 35% increase per quarter century in irrigated land in case reservoirs are built. However, the increase will still happen if proposed reservoirs are not constructed. This increase was considered to be 50% less than the expansion with the reservoir scenario”.

There is a total of 292,680 ha of existing irrigated land in the KRB (Afghanistan) and ~ 59,330 ha of potential irrigated land that may be added to the current area of irrigation [30]. Since most studies predict that there will be up to 25% irrigated land area increase in KRB, in this study, irrigated land are increased by another 30% (compares to the 15%-25% increase proposed by the WB) to account for unplanned agricultural land expansion, making it 77,129 ha. A similar trend was used on the Pakistan side of the KRB. After deducting the rain-fed and groundwater-fed irrigated lands, the potential and existing 337,309 ha irrigated land will require an additional ~1,100 Mm³ of water from the KRB flows (Table 4) in Afghanistan and Pakistan in addition to the currently consumed irrigated water of 4,055 Mm³. This constitutes 4% of the total mean annual average flow volume of the KRB flow. The irrigation water demand is considered based on low efficiency irrigation as proposed by the WB report. In case of higher efficiency of irrigation methods the study results will show a reduction in water demand. 

 

4. According to the title of the paper, i.e., "The Role of Large Dams in a Transboundary Drought Management Co-operation Framework", the paper should present the "Co-operation Framework" first, then show how dams are operated under such a framework. But in fact the framework is proposed at the end of the paper. The overall structure is not quite logical. And, it seems that the contents in section 3.5 about water rights and section 3.6 about drought management are too conceptual, not well connected with the analyses and results by model simulation.

 

Authors’ Response: One of the major constraints in transboundary drought management is inadequate water distribution. The purpose of the study is to quantify the flow regime to identify where the water can be conserved and where it should be released to serve a mutual co-operation framework.  The Subtitle topic has been changed and renumbered under 4.1 and revised to: 4.1. Transboundary KRB Water Sharing Risks and Benefits (Line 484)

 

Some specific comments:

Line 33: ‘hydrological’ or “hydrologic” drought, the expression is not consistent in the manuscript.

Authors’ Response: The term ‘hydrologic’ is now being used consistently throughout the manuscript.

 

Line 74-75: remove the remarks of literature.

Author’s Response: The referencing style was modified for this sentence.

 

Line 107, Figure 2 should focus on the case study region. Please revise the Figure 3, replace Figure 2 with the revised Figure 3, and clearly show the names (or the No. in Table 1) of locations of all dams.

Authors’ Response: The purpose of Figure 2, including the entire KRB, is to show the location of the study area and its transboundary relationship. Now the circle is highlighting the study area and the figure is renamed to read:

Figure 2. Location of the Kabul River Basin and the study area. Please refer to Lines 116-117

 

The reason that Figure 3 does not show numbers of names of the dams is due to its small size. If all names or numbers are included in Figure 2, the figure will be overloaded with texts and information. The main purpose of Figure 3 is to demonstrate the spatial relationship between existing and future proposed dams. Hence, we think the name of each individual dam is not appropriate.

 

Line 175: is the CDV the same with ADV in line 151 and ACDV in line 188? What does Qs mean in the formula?

Author’s Response: ADV is Annual Deficit Volume as first introduced in Section 2.2, near Line 151. The sentence with ADV was removed as the intention is to calculate the Cumulative Deficit Volume to determine the drought severity. The abbreviation of CDV is correct.

CDV is Cumulative Deficit Volume as first introduced in the Abstract.

 

Thank you for pointing out the error. The CDV is the Cumulative Deficit Volume. We have corrected ACDV to CDV. Please refer to line 167.

Q_s – Standard Deviation of the streamflow at selected threshold. Please refer to line 199

 

Line 178: which one is the selected threshold in the manuscript, 70%, 80%, or 90%?

Authors’ Response: The 70^th percentile threshold was selected. Please refer to line 196.

 

Line 234: please describe the hydraulic features of the future dams used in SWAT model and the set of future reservoir scenarios in detail.

Authors’ Response: The Manuscript Table 1 provides a description of hydraulic features of the proposed dam. (Line 137)

Line 141-145 also provides details of the dams’ purpose and location.

 

Line 299: the subtitle needs revision, since water rights and drought management are not belonging to low flow assessment.

Authors’ Response: Since the quantitative assessment of the KRB flow is conducted to derive policy recommendations, the transboundary competing interests should be discussed. After careful review, new section titles were assigned, and sections were rearranged.

 

Line 394: the subtitle needs revision, as the authors focused on the drought status instead of the drought index. Some of the description of SSI (Standardized Streamflow Index) should be moved to methodology item.

Authors’ Response: Thank you for an insightful recommendation (Line 165-166). The subtitle was changed from “Standardized streamflow index” to “Hydrologic Drought Duration and Standardized Streamflow Index”. The SSI description was moved from subtitle 3.4 to the subtitle Method under SSI and reads: “The Standardized Streamflow Index is a popular probability distribution function to determine the hydrologic drought by transforming the time series streamflow into a Gaussian distribution.”

 

Line 403: which timescale is the used in the manuscript.

Authors’ Response: The Study used the three timescale periods for future scenarios (01/012025 -31/12/2049) (01/01/2050 - 31/12/2074), (01/011/2075 - 31/12/2099).

 

Line 411: x-axis signature (Figure 7) should be translated into English.

Authors’ Response: The Figure title was revised to: Figure 7. The Standardized Streamflow Index (SSI) SSI Index for KRB flows at the Dakah Station without (top figure) and with (bottom figure) the low flow augmentation benefits of the proposed series of large dams.”

 

Line 499-500: the meaning of “the 2075 - 2099 scenarios under RCP 4.5 and RCP 8.5 “ is not clear.

Authors’ Response: The statement has been revised to: “While the post-reservoir flow augmentation will significantly improve the streamflow during the dry season, the drought severity is expected to increase in the last quarter century under both under RCP 4.5 and RCP 8.5.” Please also refer to Line 505-508.

Author Response File: Author Response.docx

Reviewer 2 Report

My major concerns are comments number 5, 15, and 16.

1- Please rephrase and elaborate more the following sentence in abstract (line 26): "The SSI results reveal that the proposed dams’ storage will partially address the hydrologic drought."

2- In the introduction line 42 to 45, there is a explanation on what extreme climate is. I would recommend to elaborate more on that and explain what is the connection between annual climate variations and water resources variation. Since the focus of this study is hydrological droughts. Also please add citation to this section.

3- Line 46, "Drought is an occurrence when...", what type of drought? climatological, hydrological etc. Please clarify. 

4- Line 58 to the end of sentence, please elaborate on why below zero temperature may cause drought? Since drought based on the definition presented in the manuscript is below normal water availability in forms of precipitation, streamflow and etc. If that is not what authors mean, please rephrase since it may be misleading for readers.

5- Line 64 to the end of the paragraph, please explain how building new dams may not trigger other environmental issues in the KRB. For example what other countries in that neighborhood are dealing with, such as Iran and Iraq and many other countries. In those countries, due to the construction of dams and over regulation of water resources, natural lakes, wetlands and ecological habitats are dried or drying up, which results in sand storms and air pollution, endangering biodiversity and many other catastrophic phenomena. 

6- Please describe briefly drought recovery in the intro using the following references: 

• Ahmadi, B.; Ahmadalipour, A.; Moradkhani, H. Hydrological drought persistence and recovery over the CONUS: A multi-stage framework considering water quantity and quality. Water Res. 2019, 150, 97–110. 
• Parry, S., Prudhomme, C., Wilby, R.L., Wood, P.J., (2016). Drought termination: Concept and characterisation. Prog. Phys. Geogr. 40, 743–767. https://doi.org/10.1177/0309133316652801.

7- Please change the reference to figure 2 in line 106 to figure 3, since there are no dams shown in figure 2.

8- Line 111, "The total KRB glaciers is estimated ~3.3%", percent of what? Total KRB area? The Afghan side of the KRB?

9- Figure 2 looks a bit empty, authors can add more info to it to familiarize readers with the study area. I suggest to add a raster layer to the map showing average annual precipitation over the study area.

10- What metrics were used to determine that CCSM4 is the best climate model for the KRB? (line 227)

11- Line 229 to 235, please add citations for every dataset that has been used for the study. Please make sure that every utilized dataset is cited in the manuscript.

12- I suggest adding a table listing all datasets used in the study, their spatial and temporal resolution, units, citation and etc.

13- Did authors do validation after calibrating their SWAT model? If not I highly recommend to keep a year or 2 of observed data for validation and examine the performance of the calibration.

14- A general comment on the structure of the manuscript, materials and methods are combined with some results. For example section 2.5 is presenting results while it is in the materials and method section. I would recommend to separate them and have clear boundary between each section. My suggestion is, Introduction, Materials and methods, Results, Discussion and Conclusions.

15- One of the main critique to the manuscript is the way releases from dams are assumed. In real dam operation, there are more factors that are involved with estimating/forecasting the releases. For example what is the storage level, how bad is the dry period, what is the water demand that the reservoir is supposed to supply? If a more realistic operation rules were considered in the study, table 3 wouldn't have been this optimistic. I was wondering how authors will address this issue in their study?

16- When it comes to the climate change and the potential changes for the future, the proposed method sounds a bit rough and I believe authors can design a better study to address their research questions. I highly recommend  authors to read the following paper and find inspirations and implement in their study to enrich the section 3.5:

• Karamouz, M.; Ahmadi, B.; Zahmatkesh, Z. Developing an Agricultural Planning Model in a Watershed Considering Climate Change Impacts. J. Water Resour. Plan. Manag. 2013, 139, 349–363.

17- Figure 4, please change the X axis to Date (e.g. 01/2021). Additionally, please indicate that for what time scale the SSI is calculated (for example monthly, 3-month etc.). 

Author Response

Reviewer #2

My major concerns are comments number 5, 15, and 16.

1. Please rephrase and elaborate more the following sentence in abstract (line 26): "The SSI results reveal that the proposed dams’ storage will partially address the hydrologic drought."

Authors’ Response: The SSI results show that if the proposed dams are constructed the low flow will increase by ~ 118%. This could have prevented the 2000-2002 hydrologic drought. However, the construction of the dams will not solve all the problems. In addition, in the fourth quarter of the century the drought severity may increase due further depletion of the glacier budget. The word partially was carefully used so not to make a too promising statement.

 

2. In the introduction line 42 to 45, there is a explanation on what extreme climate is. I would recommend to elaborate more on that and explain what is the connection between annual climate variations and water resources variation. Since the focus of this study is hydrological droughts. Also please add citation to this section.

Authors’ Response: We have elaborated more on the importance of the extreme events in a transboundary water resources management problem and in particular for the drought management strategy. 

 

3. Line 46, "Drought is an occurrence when...", what type of drought? climatological, hydrological etc. Please clarify.

Authors’ Response: The study has focused on hydrologic drought. Line 46 was corrected. Please refer to line 46.

 

4. Line 58 to the end of sentence, please elaborate on why below zero temperature may cause drought? Since drought based on the definition presented in the manuscript is below normal water availability in forms of precipitation, streamflow and etc. If that is not what authors mean, please rephrase since it may be misleading for readers.

Authors’ Response: The Manuscript text was revised to (Line 62-65):

“below zero temperatures may also cause hydrologic drought due to snow accumulation, freezing soils and low percolation [9].

 

5. Line 64 to the end of the paragraph, please explain how building new dams may not trigger other environmental issues in the KRB. For example what other countries in that neighborhood are dealing with, such as Iran and Iraq and many other countries. In those countries, due to the construction of dams and over regulation of water resources, natural lakes, wetlands and ecological habitats are dried or drying up, which results in sand storms and air pollution, endangering biodiversity and many other catastrophic phenomena.

Authors’ Response: We did not indicate that dam construction will only bring benefits; particularly in Table 7 we highlighted the benefits and potential impacts of the dam construction. A sentence is now added at the end of this paragraph indicating the environmental and social impacts from dam construction is possible and leading readers to Table 7.

 

6. Please describe briefly drought recovery in the intro using the following references:
   • Ahmadi, B.; Ahmadalipour, A.; Moradkhani, H. Hydrological drought persistence and recovery over the CONUS: A multi-stage framework considering water quantity and quality. Water Res. 2019, 150, 97–110.
   • Parry, S., Prudhomme, C., Wilby, R.L., Wood, P.J., (2016). Drought termination: Concept and characterisation. Prog. Phys. Geogr. 40, 743–767. https://doi.org/10.1177/0309133316652801.

 

Authors’ Response: A brief description of the drought recovery is added to the introduction with the above citations.

 

7. Please change the reference to figure 2 in line 106 to figure 3, since there are no dams shown in figure 2.

Authors’ Response: Instead of changing the figure reference, we added the reference to direct readers to look at Figures 2 and 3 as a combination.

 

8. Line 111, "The total KRB glaciers is estimated ~3.3%", percent of what? Total KRB area? The Afghan side of the KRB?

Authors’ Response: The estimated total glacier area in the study area was corrected to ~2.3%. For the entire KRB this number is ~3.3%

 

9. Figure 2 looks a bit empty, authors can add more info to it to familiarize readers with the study area. I suggest to add a raster layer to the map showing average annual precipitation over the study area.

Authors’ Response: The main purpose of Figure 2 is to show the location of KRB and its complicated relationship with all neighbours around it. Hence, we think keeping Figure 2 is appropriate.

 

 

10. What metrics were used to determine that CCSM4 is the best climate model for the KRB? (line 227)

Authors’ Response: The analysis of the CCSM4 climate models election was added that reads (Line 269-279).

 

“The selection a particular GCM climate models expends on the variety of factors such as the calibration results between the baseline data and the simulated data and comparative analysis other studies in a particular watershed. Sidiqi, 2018 recommended the CCSM4, MIROL4, BCC-CSM.1; while Hassan et.al. (2020), used BCC-CSM1. Bokhari, 2020 used, BCC-CSM1, CESM1-BGC and BNU-GDDP (Global Daily Downscaling Projections) NEX_GDDP models for the same basin.  Jahangir et.al, 2018 used the GFDL and CanESM. This study benefitted from all recommendations and has used six datasets for analysis. All six model data were compared against the baseline datasets for the KRB. The analysis included the average increase or decrease percentage of both precipitation and temperature. The analyses also included the seasonal change of the models with the baseline data and with the findings of similar climate change studies in the region by (Sahany et al., 2019; DeFlorio et al., 2013; Sayama, 2012; Bokhari, 2018; Lashkaripour, 2007; Najmuddin, 2017, Rehman, 2 020; and Sidiqi, 2018).”

 

 

11. Line 229 to 235, please add citations for every dataset that has been used for the study. Please make sure that every utilized dataset is cited in the manuscript.

Authors’ Response: We have checked and confirm that all datasets used in the study are cited in the manuscript.

 

12. I suggest adding a table listing all datasets used in the study, their spatial and temporal resolution, units, citation and etc.

 

Authors’ Response: We have added a table listing all datasets used in the study including their spatial and temporal resolution. Please refer to Table 2. Line  269.

 

13. Did authors do validation after calibrating their SWAT model? If not I highly recommend to keep a year or 2 of observed data for validation and examine the performance of the calibration.

Authors’ Response: The model validation was conducted for 2011-2013. The results of the model validation associated with the paper is.

Table A6. Goodness-of-fit statistics and associated qualitative ratings of model calibration and validation

Station	Periods	p-factor	r-factor	PBIAS	NSE	R2	Overall rating
Dakah	Validation (2011-2013)	0.71	0.86	-0.69%	0.73	0.82	Good

 

 

 

14. A general comment on the structure of the manuscript, materials and methods are combined with some results. For example section 2.5 is presenting results while it is in the materials and method section. I would recommend to separate them and have clear boundary between each section. My suggestion is, Introduction, Materials and methods, Results, Discussion and Conclusions.

Authors’ Response: The Manuscript titles have been modified as per your recommendation. Thank you for the insightful recommendations.

Subtitle “The SWAT Model of the KRB flows” was moved to 2.6 and the SWAT modelling description as added that reads (Line 384-398). ”The Soil and Water Assessment Tool (SWAT) developed by the Department of Agriculture was used to model the hydrologic processes across the globe and, in particular, in large river basins and data-poor regions (Arnold et al., 2012; Daggupati et al., 2015). SWAT is a semi-distributed model that generates a stream network using the Digital Elevation Model (DEM) and divides the subject watersheds into smaller sub-watersheds and then into Hydrologic Response Units (HRUs) using unique combinations of land use, soil type, and surface slope. The modeling used for the hydrology considered the volumes and spatial extent of snowpack and subsequent snowmelt, allowing spatial variations using a maximum of ten elevation bands in a sub-basin (Neitsch et al., 2011) to simulate the hydrologic processes in cold mountain areas such as the KRB.

 

3.2 Existing and future irrigated land and its water demand was moved to 2.5 in the Materials and Methods and Data acquisition section (Line 296).

 

15. One of the main critique to the manuscript is the way releases from dams are assumed. In real dam operation, there are more factors that are involved with estimating/forecasting the releases. For example what is the storage level, how bad is the dry period, what is the water demand that the reservoir is supposed to supply? If a more realistic operation rules were considered in the study, table 3 wouldn't have been this optimistic. I was wondering how authors will address this issue in their study?

Authors’ Response: The Manuscript text was revised to (Line 441-4451):

“The proposed reservoir operations’ procedures were assumed based on the monthly reservoir operation targets. The reservoir routing in the SWAT model was conducted based on the storage assigned for different months in flood and non-flood seasons. The reservoir water release was also synchronised in the model based on the monthly water demand as per the WB, 2010 report.” Irrigation demand is high during April to August (12.7%, 17.1%, 25.1%, 15.6%, of annual water demand respectively) followed by decreased demands from September to March (3.1%, 2.8%, 3.0%, 3.1%, 2.9%, 5.3%, of annual water demand respectively . The dam operation is guided by two major factors, a) the monthly water demand and b) the peak flow season. It is assumed that at any given season before the next seasons fill up, 50% of the stored water will be released for low flow augmentation and having space in the reservoir for the upcoming season peak flows. However, this method may be under the influence of various uncertainties. These uncertainties are related to precipitation, temperature variability, and other knowledge gaps, including technical information and management practices that should be considered in future studies. The study accounted for increased irrigated land expansion, and storage capacity. It is our understanding that despite these uncertainties, low flow augmentation will significantly increase the low flow during the dry season. Considering possible uncertainties, we used the term “partially addressing the hydrologic drought” in the Abstract (line 27).

 

16. When it comes to the climate change and the potential changes for the future, the proposed method sounds a bit rough and I believe authors can design a better study to address their research questions. I highly recommend authors to read the following paper and find inspirations and implement in their study to enrich the section 3.5:

Karamouz, M.; Ahmadi, B.; Zahmatkesh, Z. Developing an Agricultural Planning Model in a Watershed Considering Climate Change Impacts. J. Water Resour. Plan. Manag. 2013, 139, 349–363.

Authors’ Response: We have read the suggested article and agree that future studies that are more refined can be conducted. The scope of this initial study was to focus on advantages and limitations of a series of large dams in water resources management for a transboundary Kabul River Basin. Karamouz et al. (2013) discuss agricultural water demand and planning issues (this work was cited).  

 

17. Figure 4, please change the X axis to Date (e.g. 01/2021). Additionally, please indicate that for what time scale the SSI is calculated (for example monthly, 3-month etc.).

Authors’ Response: Figure 4 x-axis has been modified. Please refer to Line 380.

 

Author Response File: Author Response.docx

Reviewer 3 Report

The legend in Figure 1 should be corrected - Afg Boundary - Afghanistan?

Line 180 - Vicente-Serrano et al [5].

Change the description of the vertical axes in Figure 6 to Mean monthly flow (left) and Cumulative flow volume (right)

Complete the formula numbering.

Provide an explanation of what m means (Line 162)

Provide an explanation of what Qs means (Line 175).

The description of the horizontal axis in Figure 6 should be corrected.

The purpose of the paper should be better highlighted.

Correct according to the guidelines for authors (Line 73-76).

The "Results and discussion" section should be distinguished.

The section discussion of results should be completed.

Author Response

Reviewer #3

• The legend in Figure 1 should be corrected - Afg Boundary - Afghanistan?

Authors’ Response: The Figure 1 Legend has been corrected (Line 116).

 

• Line 180 - Vicente-Serrano et al [5].

Authors’ Response: This has been corrected.

 

• Change the description of the vertical axes in Figure 6 to Mean monthly flow (left) and Cumulative flow volume (right)

Authors’ Response: The axis title has been modified.

 

• Complete the formula numbering.

Authors’ Response: Formulas in the manuscript are now numbered.

 

• Provide an explanation of what m means (Line 162)

Authors’ Response: µ  is the Mean of the logarithmically transformed streamflow (Line 180)

 

• Provide an explanation of what Qs means (Line 175).

Authors’ Response: explanation is added.

 

• The description of the horizontal axis in Figure 6 should be corrected.

Authors’ Response: the horizontal axis in Figure 6 is improved.

 

• The purpose of the paper should be better highlighted.

Authors’ Response: The paper was revised to better highlight the purpose (Line 82-86).

”The main goal of this paper is to study the impacts of the climate change on KRB flow regime, and investigate the benefits of the proposed reservoirs to retain water for the purposes of low flow augmentation. The issue of ‘steady’ flow to Pakistan from the Dakah outlet is a transboundary matter and the low flow has always been a matter of contention between the two nations. These contentions and grievances are more visible during hydrologic drought events.”

• Correct according to the guidelines for authors (Line 73-76).

Authors’ Response: Referencing style has been modified.

 

• The "Results and discussion" section should be distinguished.

Authors’ Response: The Results and Discussion sections have been distinguished.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

1. The title of paper does match its content. As the author stated, "The main goal of this paper is to study the impacts of the climate change on the KRB flow regime and the potential benefits of the new reservoirs to retain water for the purposes of low flow augmentation", it does talk much about "a Transboundary Drought Management Co-operation Framework", which should be the focus of the paper according to the title. In fact, the so called "Transboundary Drought Management Co-operation Framework", which should be the core of the study, is only described as some rough principles in Section 4.2 without any quantitative support of modelling results, and the result about the impacts of climate change is weak. 
2. As for the data，where are the ten climate stations which are used to evaluate CFSR data?? They should be presented in Figure 2 or Figure 3. 
3. The method was not improved much, espeically nothing about how to operate dams to manage transboundary drought. The author replied that "Dam Operation: the Manuscript text was revised as (Line 441-445):  The proposed reservoir operations procedures were assumed based on the monthly reservoir operation targets. ......" First of all, it should be Line 435-439. More importantly, what's the meaning of "the monthly reservoir operation targets", and the title of the paper talks about the role of large dams for drought management, but there is nothing about management at all.
4. It is stated that "During the model setup, based on the available information, 80% of irrigation water was assumed from surface water (dams), while 20% 340 was assumed from groundwater and precipitation".  Is there any support for this setup?
5. The estimation of SSI is quite doubtful. As a standardized series, SSI should most varies between +2 ~ -2，and approximately 16% falls below -1.  But the results presented in Figure 7 show that the SSI for the situation either without future dams or with future dam mostly falls between +0.5 ~-0.5. There should be some explanation for the results.
6. The organization of the paper is still not satisfying. For instance, 
(1) Figure 1 is about the method of the study, should be put in Section 2.2.
(2) Section 2.4, which describes the data used, and Section 2.5， which describes the situation of the irrigation, should be moved after Section 2.1. 
(3) Line 462-465 and Table 7 should be moved to the Section 2.2.
7. About figures, the map extent in Figure 2 is too large. Please focus on Pakistan. There is definitely enough space to present all the numbers in Table 1 if Figure 3 is enlarged and the labels are well arranged

Author Response

Reviewer #1 Comments:

Comments and Suggestions for Authors

1. The title of paper does not match its content. As the author stated, "The main goal of this paper is to study the impacts of the climate change on the KRB flow regime and the potential benefits of the new reservoirs to retain water for the purposes of low flow augmentation", it does talk much about "a Transboundary Drought Management Co-operation Framework", which should be the focus of the paper according to the title. In fact, the so called "Transboundary Drought Management Co-operation Framework", which should be the core of the study, is only described as some rough principles in Section 4.2 without any quantitative support of modelling results, and the result about the impacts of climate change is weak. 

Authors’ Response:

We believe that the title of the paper accurately matches its content “The Role of Large Dams in a Transboundary Drought Management Co-operation Framework – Case Study of the Kabul River Basin”. However, we do agree that the Manuscript should reflect the transboundary cooperation framework. We have revised the manuscript to put more emphasis on the transboundary drought management to establish the need for a science-based drought management framework using the computer modeling to provide the essential information for an open and transparent transboundary management. As for discussion of the framework, we have highlighted that the framework can only be based on magnitudes and hence, need the models described in the paper, to provide the science behind the policy framework.

Line 589 -595 provides a connection between the FAO three major transboundary drought risk management and the current study modelling process. The paper Table 8 (line 556) and Table 9 (Line 595) also provide evidence of a transboundary cooperation approach to drought risk management. Section 4.2 (Line 576) is, in fact, dedicated to this matter.

 

The introduction was revised to include:

“The climate change impact has been considered in the pre- and post-reservoirs emission scenarios (RCP4.5 and RCP8.5). Table 7 (line 501) under S0, S1 and S2 are indicating the climate change impacts on flow regime under pre-reservoir and post-reservoirs scenarios.”

The Methods part was enriched based on your recommendations that reads (Lines 154-169) 

“Ahmadi et al.(2019) described two groups of drought identification methods a) probability and statistical calculation based method b) Threshold-based method (constant percentile of annual long-term cumulative frequency distribution and variable threshold). Both of Ahmadi et al. methods require long time series of hydro-meteorological data. The variable method requires the daily quantiles calculation for the streamflow duration curve over the entire observation period (Ahmadi et al, 2019). Another important aspect of drought identification and monitoring is the drought termination.  The end of a drought is the critical time during which water resource managers urgently require information on the replenishment of supplies (Parry et al.,  2016). Drought termination is associated with notable hydro meteorological events making the end of drought far more critical than the drought itself (Parry et al., 2016).

The variable threshold considers the short term drought identification and recovery, and the drought termination is looking at a specific timeline of a hydrologic events and are important knowledge for local managers and agricultural community. This study is more focused on the longer hydrologic drought, ignoring shorter events (after Hisdal et al., 2004) and is concentrated on the policy formulation and transboundary efforts in drought management during the entirety of this hydrologic event including occurrence, termination and recovery.”  

2. 
   As for the data where are the ten climate stations which are used to evaluate CFSR data?? They should be presented in Figure 2 or Figure 3. 

Authors’ Response:

Figures 2 and 3 were amalgamated. The revised figure shows the climate stations, existing and proposed reservoirs. Please refer to Figure 1. Line 122-123

3. 
   The method was not improved much, especially nothing about how to operate dams to manage transboundary drought. The author replied that "Dam Operation: the Manuscript text was revised as (Line 441-445):  The proposed reservoir operations procedures were assumed based on the monthly reservoir operation targets. ......" First of all, it should be Line 435-439. More importantly, what's the meaning of "the monthly reservoir operation targets", and the title of the paper talks about the role of large dams for drought management, but there is nothing about management at all.

Authors’ Response:

Thank you for the valuable comment. The paper was improved in the area of methods (Lines 153-168). In particular, the paper considered your comments and recommendations to explain the simplified methodology behind reservoirs target operation management. Please refer to Lines (435-448) as reads:

“The World Bank (2010) report identified the monthly water demand for the agricultural land in KRB [30]. The KRB low flow seasons are October to March where the water demand for agricultural lands is also low on the Afghanistan side of the KRB. The proposed reservoirs/dams are based on the variables a) irrigation water demand, b) hydropower water demand, c) flood mitigation, d) environmental water demand. The SWAT modelling considered the reservoir operation  schedule based on the above variables and has estimated the percentage of the reservoirs water release and flood routing based on Reservoir Operation Volume targets. The proposed reservoirs being considered will have a total capacity of 7,140 Mm³ of which 50% is assumed to be ‘active’ storage and hence, water in the active storage for each reservoir is released by April, ahead of the flood season (as shown in Figure 5). The period of water storage season is from April to August. The SWAT database was assigned with the target release percentage at each month based on the above variables. The modeling also considered that the minimum flow will always be equal or more to the historical low flows for recreational and environmental purposes. This includes the post construction fill up of reservoirs”.

4. It is stated that "During the model setup, based on the available information, 80% of irrigation water was assumed from surface water (dams), while 20% was assumed from groundwater and precipitation".  Is there any support for this setup?

Authors’ Response:

Qureshi (2002), World Bank (2010), and Walter (2014) have studied the irrigation methods in Afghanistan, in general, and in the KRB in particular. They report that about 80% of irrigation water is supplied from surface water sources (rivers), the ground water use is around 15% and roughly 5% are rainfall fed irrigation. Please refer to line 130 of the revised manuscript.

5. 
   The estimation of SSI is quite doubtful. As a standardized series, SSI should most varies between +2 ~ -2，and approximately 16% falls below -1.  But the results presented in Figure 7 show that the SSI for the situation either without future dams or with future dam mostly falls between +0.5 ~-0.5. There should be some explanation for the results.

Authors’ Response:

The explanation for the different SSI in the KRB is provided in Lines (512-521) as reads:

“The KRB average annual temperature is around 8ºC. It is below the average in the surrounding basins. Most of the study area is mountainous with higher snow storage capacity, higher runoff coefficient and Curve Number. The milder drought graph can be explained by the above terrain and climatic conditions. However, in the steeper areas (eastern provinces of Afghanistan and in the KRB Pakistan) drought longevity is a serious matter.  The results show that the KRB is not experiencing +2 and ~ -2 drought severity index which are severe drought or wet climate. The KRB is more associated with mild and moderate drought that is hydrologic and seasonal in nature. This type of drought can deplete agricultural products in the economically weak regions. In areas with severe poverty and lack of access to services and resources this type of drought can have devastating effects on the population”.

6. The organization of the paper is still not satisfying. For instance, 
   (1) Figure 1 is about the method of the study, should be put in Section 2.2.
   (2) Section 2.4, which describes the data used, and Section 2.5， which describes the situation of the irrigation, should be moved after Section 2.1. 
   (3) Line 462-465 and Table 7 should be moved to the Section 2.2.
7. About figures, the map extent in Figure 2 is too large. Please focus on Pakistan. There is definitely enough space to present all the numbers in Table 1 if Figure 3 is enlarged and the labels are well arranged

Authors’ Response:

• Figure 1 was moved from Introduction to Methods section under the name of Figure 2. (Line 254)
• Since this topic is part of the Method, and within the same section, we prefer to keep it under 2.4
• We agree with the reviewer’s comment regarding Table 7. This table was moved to Methods under the name of Table 2.(Line 224)
• The study area is focused on the basin with the outlet located at Dakah station. This is mostly the Afghanistan In this study the Pakistan-based planned dams are not accounted for. However, the majority of the focus is on how downstream Pakistan can benefit from an equitable incentive-based balanced flow regime. 

Reviewer 2 Report

Thank you for addressing most of comments in the revision. I still couldn't find drought recovery explanation section in the introduction. For authors reference, I provide them with my previous comment. I was expecting addressing comments thoroughly in the revised manuscript. Other than that I don't have any further comments.

"Review 1: 

Please describe briefly drought recovery in the intro using the following references:

• • Ahmadi, B.; Ahmadalipour, A.; Moradkhani, H. Hydrological drought persistence and recovery over the CONUS: A multi-stage framework considering water quantity and quality. Water Res. 2019, 150, 97–110.
  • Parry, S., Prudhomme, C., Wilby, R.L., Wood, P.J., (2016). Drought termination: Concept and characterisation. Prog. Phys. Geogr. 40, 743–767. https://doi.org/10.1177/0309133316652801."

Author Response

Reviewer #2 Comments:

Comments and Suggestions for Authors

Thank you for addressing most of comments in the revision. I still couldn't find drought recovery explanation section in the introduction. For authors reference, I provide them with my previous comment. I was expecting addressing comments thoroughly in the revised manuscript. Other than that I don't have any further comments.

Please describe briefly drought recovery in the intro using the following references:

• Ahmadi, B.; Ahmadalipour, A.; Moradkhani, H. Hydrological drought persistence and recovery over the CONUS: A multi-stage framework considering water quantity and quality. Water Res. 2019, 150, 97–110.
• Parry, S., Prudhomme, C., Wilby, R.L., Wood, P.J., (2016). Drought termination: Concept and characterisation. Prog. Phys. Geogr. 40, 743–767. https://doi.org/10.1177/0309133316652801."

Authors’ Response:

We benefitted from the two papers suggested. While the manuscript is more focused on water quantity, these papers provided valuable insights into the drought recovery and stages. The manuscript was therefore revised in several areas to reflect the recommendation: The Methods part was enriched based on your recommendations that reads (Lines 154-169):

“Ahmadi et al. (2019) described two groups of drought identification methods a) probability and statistical calculation-based method b) Threshold-based method (constant percentile of annual long-term cumulative frequency distribution and variable threshold). Both methods require long time series of hydro-meteorological data. The variable method requires the daily quantiles calculation for the streamflow duration curve over the entire observation period (Ahmadi et al., 2019). Another important aspect of drought identification and monitoring is the drought termination.  The end of a drought is the critical time during which water resource managers urgently require information on the replenishment of supplies (Parry et al., 2016). Drought termination is associated with notable hydro meteorological events making the end of drought far more critical than the drought itself (Parry et al., 2016).

The variable threshold considers the short-term drought identification and recovery, and the drought termination is looking at a specific timeline of hydrologic events and are important knowledge for local managers and the agricultural community. This study is more focused on the longer hydrologic drought ignoring shorter events (as per Hisdal et al., 2004) and is concentrated on the policy formulation and transboundary efforts in drought management during the entirety of this hydrologic event including occurrence, termination and recovery.”