Is Sustainable Watershed Management Feasible under Climate Change? An Economic Appraisal of the Nile River
Round 1
Reviewer 1 Report
The article has scientific and practical value. The results are interesting and have high impact and global relevance for publication in an international journal.
Author Response
Thank you for your time and valuable comments.
Reviewer 2 Report
Review for sustainability-645531 “Is Sustainable Watershed Management Feasible under Climate Change? An Economic Appraisal of the River Nile”
7 November, 2019
This study produced an economic optimization model to understand how climate change and uncertainties will affect the Nile River, its management, and economics throughout three future periods. The authors used net social present values and downstream damage estimates to determine that hydro-suction sediment removal is the most feasible form of watershed management for future climates. If no watershed management controls are used, damages downriver were estimated to be $763.6 billion, but the use of controls such as HSRS could lead to an NSPV of $255.6 billion. A sensitivity analysis was also performed, and the findings are a good start for future research.
I found the article generally easy to follow and an interesting read. It has important applications for watershed management along the river and for future research. I give my critiques with the goal of providing constructive feedback. My main critiques involve a need for background on methods and concepts, and for a discussion section that ties the findings with existing research.
Abstract and Introduction: I feel the goals and objectives of the study could be stated more clearly. Add a sentence to the abstract and introduction that clarifies the objectives. For example, the abstract sentence (line 18) that states “In this sense, this paper attempts to solve heterogeneous problems by introducing an economic optimization approach with uncertainty (i.e. climate change)” is confusing to me. Rewording as “The purpose of our study was to use an economic optimization approach to evaluate if sustainable management of the Nile River is feasible concerning climate change” would make more sense to me. I would do the same for the similar Introduction sentence on pg. 2 line 79.
Pg. 1, line 22. The abstract states that “among technically feasible sediment removal schemes, the HSRS is the most desirable”. Does this contradict what is stated on pg. 9, line 285 that HSRS is the only feasible scheme? If so, you should clarify that HSRS was the only technically feasible scheme. Also, do you have any references that support HSRS being the only feasible scheme?
Pg. 1, line 38. It is unclear what the citation is for the sentence that begins “For example, in the hydrologic cycle…” Clarify this.
Pg. 7, line 254. It is unclear what the citation is for the sentence that begins “Unfortunately, some researchers…” Clarify this.
Table 1. Rename mean water flow (BCM) as mean annual water inflow (BCM) so it is more specific.
Pg. 9, line 295. The Shim et al. study that is referenced describes the procedure for South Korea only. Add some more details about the downscaling process as used for the Nile.
Pg. 10, line 317. Provide the NSPV abbreviation, “net social present value (NSPV)”. Also, the first time NSPV is mentioned is in the results. Where is it calculated in the explanation of the equations? Provide some background on the measure, such as a brief description, and cite previous studies that have used it.
Pg. 10, line 324. Where do the $100 and $200 million initial construction costs come from? How do they fit into the model? Provide an explanation of these numbers.
Pg. 10, line 350. What is NSPC? Is it a typo?
Table 3. This table helps me make sense of the results greatly. I do suggest organizational improvements for it though. First, from this table I can tell how NSPV is calculated, though I don’t see it explained in the text or caption. Explain this in the manuscript text and table caption. Second, the NSPV and DL columns for RCP2.6 are very tall and narrow, and need to be fixed. This causes the rows to be about 8x as tall as they need to be, which makes the table not fit on one page. The table should either all fit on one page, or be divided into 2 tables each with separate headers. Third, instead of the term “Climate Change” in the upper left corner, it would help to name the column “Management scenario,” then expand the caption “Simulation results under different RCP scenarios and management scenarios, including the use of hydro-suction sediment removal system (HSRS) (Unit: billion USD).” That would better explain what is contained within the table. Fourth, turn the second row of the table with benefit/damage abbreviations into a second line of table header, so it’s not confused with the observations. Also, put an * on the U, D, Ds, Da, NSPV, and DL headers that directs readers to the * footnote. These changes should make the table better organized and easier to interpret.
4.2 Sensitivity Analysis: The results section is the first time that the sensitivity analysis is brought up in the manuscript. I don’t understand it without being provided a background on its purpose and methods. Update the methods and maybe introduction sections of the manuscript to provide a background on sensitivity analysis and the technique you used to perform it. Include an explanation of the “restricted (X-bar)” and “restricted (S)” alternatives for HSRS strategies (a) and (b). Are they the sample mean and standard deviation? If so, why does strategy (a) get the mean and (b) get the standard deviation?
5. Conclusions. This section reads more like a discussion of the results. Perhaps change the name to “Discussion.” Also, this would be a good opportunity to discuss the results of the study amongst findings of other studies. Do other studies tend to support the findings of the model? Are there studies in the Nile that had opposing findings about sediment control? What about studies for other watersheds that have used similar techniques? Try to tie in the findings with existing research. This could help provide credibility to the model and evaluate its effectiveness
Author Response
Reviewer's Commment: This study produced an economic optimization model to understand how climate change and uncertainties will affect the Nile River, its management, and economics throughout three future periods. The authors used net social present values and downstream damage estimates to determine that hydro-suction sediment removal is the most feasible form of watershed management for future climates. If no watershed management controls are used, damages downriver were estimated to be $763.6 billion, but the use of controls such as HSRS could lead to an NSPV of $255.6 billion. A sensitivity analysis was also performed, and the findings are a good start for future research. I found the article generally easy to follow and an interesting read. It has important applications for watershed management along the river and for future research. I give my critiques with the goal of providing constructive feedback. My main critiques involve a need for background on methods and concepts, and for a discussion section that ties the findings with existing research. Response: Thank you for your comments.
Reviewer's Commment: Abstract and Introduction: I feel the goals and objectives of the study could be stated more clearly. Add a sentence to the abstract and introduction that clarifies the objectives. For example, the abstract sentence (line 18) that states “In this sense, this paper attempts to solve heterogeneous problems by introducing an economic optimization approach with uncertainty (i.e. climate change)” is confusing to me. Rewording as “The purpose of our study was to use an economic optimization approach to evaluate if sustainable management of the Nile River is feasible concerning climate change” would make more sense to me. I would do the same for the similar Introduction sentence on pg. 2 line 79. Response: We have changed sentences based on your comment. The sentence in line 18-20 at page 1 was rewritten to read as follows: "The purpose of our study is to use an economic optimization approach to evaluate the feasibility of sustainable management of the Nile concerning climate change." The sentence in line 78-79 at page 2 was rewritten to read as follows: "In this sense, the purpose of our study is to present an economic optimization approach to evaluate if sustainable management of the Nile River is feasible under climate change."
Reviewer's Commment: Pg. 1, line 22. The abstract states that “among technically feasible sediment removal schemes, the HSRS is the most desirable”. Does this contradict what is stated on pg. 9, line 285 that HSRS is the only feasible scheme? If so, you should clarify that HSRS was the only technically feasible scheme. Also, do you have any references that support HSRS being the only feasible scheme? Response: We agree and have changed sentences based on your comment. The sentence in line 22-24 was rewritten to read as follows: "The results indicate that among the various technically feasible sediment removal schemes, the hydro-suction sediment removal system (HSRS) is the only desirable solution under severe climate change."
Reviewer's Commment: Pg. 1, line 38. It is unclear what the citation is for the sentence that begins “For example, in the hydrologic cycle…” Clarify this. Response: To clarify this, the sentence in line 37-40 was rewritten to read as follows: "For example, in rivers, an increase in temperature causes a rise in the evaporation rate which leads to a reduction in incoming water flow from upstream to downstream. The situation can be worsened when there is a dam downstream, since the decreased incoming water flow will eventually reduce the value of a reservoir [2]."
Reviewer's Commment: Pg. 7, line 254. It is unclear what the citation is for the sentence that begins “Unfortunately, some researchers…” Clarify this. Response: We agree and to clarify this, the sentences line 272-275 was rewritten to read as follows: "Unfortunately, Conway and Hulme [17] indicated that the River Nile’s water flow could decrease by up to 40% due to climate change impacts. They also estimated that a 1oC increase in temperature would lead to a 4% storage loss in the AHD due to evaporation."
Table 1. Rename mean water flow (BCM) as mean annual water inflow (BCM) so it is more specific. Response: We agree and changed in our revised manuscript
Reviewer's Commment: Pg. 9, line 295. The Shim et al. study that is referenced describes the procedure for South Korea only. Add some more details about the downscaling process as used for the Nile. Response: We appreciate the comment on the wrong reference that has been changed to the right one [26].
Reviewer's Commment: Pg. 10, line 317. Provide the NSPV abbreviation, “net social present value (NSPV)”. Also, the first time NSPV is mentioned is in the results. Where is it calculated in the explanation of the equations? Provide some background on the measure, such as a brief description, and cite previous studies that have used it. Response: We agree and provided the NSPV abbreviation in line 338. Since we provided a discount rate, equation or description of this may not be necessary.
Reviewer's Commment: Pg. 10, line 324. Where do the $100 and $200 million initial construction costs come from? How do they fit into the model? Provide an explanation of these numbers. Response: We added references and it is fitted in the model as a cost parameter when we executed optimization process.
Reviewer's Commment: Pg. 10, line 350. What is NSPC? Is it a typo? Response: Yes, it is a typo, we fixed it.
Reviewer's Commment: Table 3. This table helps me make sense of the results greatly. I do suggest organizational improvements for it though. First, from this table I can tell how NSPV is calculated, though I don’t see it explained in the text or caption. Explain this in the manuscript text and table caption. Response: The way that NSPV is calculated is explained in equation (19).
Reviewer's Commment: Second, the NSPV and DL columns for RCP2.6 are very tall and narrow, and need to be fixed. This causes the rows to be about 8x as tall as they need to be, which makes the table not fit on one page. The table should either all fit on one page, or be divided into 2 tables each with separate headers. Response: We don’t know why but this seems like editing error or converting problem. We provided the result table as horizontal page. In our manuscript, it is hard to find any misreading problem. Please see revised version of manuscript.
Reviewer's Commment: Third, instead of the term “Climate Change” in the upper left corner, it would help to name the column “Management scenario,” then expand the caption “Simulation results under different RCP scenarios and management scenarios, including the use of hydro-suction sediment removal system (HSRS) (Unit: billion USD).” That would better explain what is contained within the table. Response: Thanks for your comment, we changed as you mentioned.
Reviewer's Commment: Fourth, turn the second row of the table with benefit/damage abbreviations into a second line of table header, so it’s not confused with the observations. Also, put an * on the U, D, Ds, Da, NSPV, and DL headers that directs readers to the * footnote. These changes should make the table better organized and easier to interpret. Response: Thanks for your comment, we changed as you mentioned.
Reviewer's Commment: 4.2 Sensitivity Analysis: The results section is the first time that the sensitivity analysis is brought up in the manuscript. I don’t understand it without being provided a background on its purpose and methods. Update the methods and maybe introduction sections of the manuscript to provide a background on sensitivity analysis and the technique you used to perform it. Include an explanation of the “restricted (X-bar)” and “restricted (S)” alternatives for HSRS strategies (a) and (b). Are they the sample mean and standard deviation? If so, why does strategy (a) get the mean and (b) get the standard deviation? Response: X-bar and S in the table were Typos. We fixed them. We explained why the sensitivity analysis is necessary for and methods are very common. To clarify this, the sentences line 380-386 was rewritten to read as follows: "Although it is well known that future values are very sensitive to interest rate, the role of the HSRS in the entire watershed becomes much more important when climate conditions of the Nile watershed change. Furthermore, the HSRS effect on altering nutrient deposition to downstream agriculture impacts the social planner’s decision making. Since the model assumes that only 7% of nutrients are deposited to downstream agricultural land by the HSRS, we conduct the sensitivity analysis by introducing 30% of the nutrient deposition rate to downstream agriculture. The result can be found in Table 4."
Reviewer's Commment: 5. Conclusions. This section reads more like a discussion of the results. Perhaps change the name to “Discussion.” Also, this would be a good opportunity to discuss the results of the study amongst findings of other studies. Do other studies tend to support the findings of the model? Are there studies in the Nile that had opposing findings about sediment control? What about studies for other watersheds that have used similar techniques? Try to tie in the findings with existing research. This could help provide credibility to the model and evaluate its effectiveness. Response: Our findings are elaborated the way you suggested.
We, authors, appreciated all your valuable corrections and comments to improve the quality of our current manuscript.
Reviewer 3 Report
This manuscript provided a mathematical derivation of optimized benefits considering upstream farmers, reservoir level, and the downstream watershed, and apply the equations to the Nile River watershed. Generally, the manuscript is well composed, but the reviewer would like to point out the following issues. In summary, the manuscript used many relationships that were not defined, or the definitions were not supported. The main idea of this manuscript is good, but the presentation still needs a lot of work.
Writing is generally good, but some minor mistakes in grammar are visible. For example, line 14 should be “…a well-known transboundary river…” Such mistakes are easy to spot and the free functions of several software packages (such as Grammarly) can handle it quite well. Please review the whole document for grammar issues. In Equation 1, the parameters of r and A are not explained. In fact, several key functions were not defined well in Equation 1. For example, how are Y and C defined? If they are fundamental parameters in some niche fields, please provide references for them. The construction of NBUF itself is unsupported either. Similar issues also apply to other major equations in this manuscript. This is the main issue with this manuscript. Please unify the usage of subscripts. For example, Zpr in Equation 7 does not use subscription, but its definition at line 140 does. Please check the whole manuscript for similar issues. Line 156: the definition of Xt is too vague. From later sections, it is a function of time, but the definition here does not give that out. Line 212: Is the control variable Chi (Greek alphabet of X) or X (English alphabet)? Both representations have been used for different parameters in the manuscript. Chi looks like what was used here, but Equation 20 used X. Line 212: The parameter of Fs was not defined before. Line 212: Why are these variables the control variables? There is no explanation whatsoever before. This should be discussed at least in the introduction section. Lines 220, 221: How are the “co-state” equations formed? Line 242: Please elaborate on how the optimization was done. You have five 1st-order derivative equations and two “co-state” equations. How were they used together in this case? Table 1: not all parameter values were defined here. Besides, these values are likely to be the average value. Please perform a sensitivity analysis and a Monte Carlo analysis to see how the variation of the parameters can do to your results. The sensitivity analysis in Table 4 is not sufficient.
Author Response
Reviewer's Commment: This manuscript provided a mathematical derivation of optimized benefits considering upstream farmers, reservoir level, and the downstream watershed, and apply the equations to the Nile River watershed. Generally, the manuscript is well composed, but the reviewer would like to point out the following issues. In summary, the manuscript used many relationships that were not defined, or the definitions were not supported. The main idea of this manuscript is good, but the presentation still needs a lot of work. Response: Thanks for your comments.
Reviewer's Commment: Writing is generally good, but some minor mistakes in grammar are visible. For example, line 14 should be “…a well-known transboundary river…” Such mistakes are easy to spot and the free functions of several software packages (such as Grammarly) can handle it quite well. Please review the whole document for grammar issues. Response: Thanks for your comments. We looked over the entire manuscript to check grammar issues.
Reviewer's Commment: In Equation 1, the parameters of r and A are not explained. In fact, several key functions were not defined well in Equation 1. For example, how are Y and C defined? If they are fundamental parameters in some niche fields, please provide references for them. The construction of NBUF itself is unsupported either. Similar issues also apply to other major equations in this manuscript. This is the main issue with this manuscript. Response: In equation 1, A was already defined and we have included explanation of r. In addition, Y and C is defined in the paragraph. We included a reference as you mentioned.
Reviewer's Commment: Please unify the usage of subscripts. For example, Zpr in Equation 7 does not use subscription, but its definition at line 140 does. Please check the whole manuscript for similar issues. Response: We fixed this as you mentioned.
Reviewer's Commment: Line 156: the definition of Xt is too vague. From later sections, it is a function of time, but the definition here does not give that out. Line 212: Is the control variable Chi (Greek alphabet of X) or X (English alphabet)? Both representations have been used for different parameters in the manuscript. Chi looks like what was used here, but Equation 20 used X. Line 212: Response: Xt in line 174 in revised manuscript is an English alphabet and in equation 20 it is the same one. But Chi is used in the Hamiltonian equation and upstream, it is already defined.
Reviewer's Commment: The parameter of Fs was not defined before. Line 212: Why are these variables the control variables? There is no explanation whatsoever before. This should be discussed at least in the introduction section. Lines 220, 221: How are the “co-state” equations formed? Line 242: Please elaborate on how the optimization was done. You have five 1st-order derivative equations and two “co-state” equations. How were they used together in this case? Response:Fs mean F1 and F2, we fixed those. Setting up control variables and co-state equation are done by the common dynamic optimization approach (i.e. Hamiltonian). Since storage capacity and soil depth are decreased overtime, we can apply dynamic approach here.
Reviewer's Commment: Table 1: not all parameter values were defined here. Besides, these values are likely to be the average value. Please perform a sensitivity analysis and a Monte Carlo analysis to see how the variation of the parameters can do to your results. The sensitivity analysis in Table 4 is not sufficient. Response: Since the approach used in this research is the Hamiltonian, not estimation, there is no distribution of parameters here. Thus, a Monte Carlo is inappropriate. And the value in table 1 is not an average value, those are calculated based on the dynamic model. Therefore, we reported the value of all the stakeholder’s benefits and damages, not the value of parameters. However, we fixed table 4 and its explanations.
We, authors, appreciated all your valuable corrections and comments to improve the quality of our current manuscript.
Round 2
Reviewer 3 Report
Thank you for providing a revised manuscript quickly. The reviewer appreciates the authors' efforts. However, it appears that the manuscript was only minimally revised. The reviewer would like to point out several lingering issues:
1. The derivation and example are exclusively targetted to the application area and the equations are in lack of flexibility for general applications. There are a lot of assumptions made to the relations between variables, which may or may not be realistic. The reviewer suggests changing the submission to a "case report" or "concept paper". The latter is probably more suitable.
2. The reviewer does not understand why the Nile River was chosen as the application example? None of the authors are currently working in that area. Why don't you choose a more familiar study area so that the result can be more realistic?
3. Pursuant to the previous point, the study area is huge, so it is unlikely that the value for any variable will stay constant throughout the study area. If the authors cannot provide an accurate spatial distribution of all variables, some kind of error estimate for the result should be provided. The reviewer recall that Hamiltonian Monte Carlo is indeed an available technique. Please try to explore the influence of variation of variables to the result.
4. The optimization process is still vaguely described. Like the reviewer said before, a major revision to the manuscript is necessary. In addition, some of the reviewer's old questions are still not answered either in the response or in the manuscript. For example, how the control variables are defined is still absent either in the manuscript or in the response.
Author Response
1. The derivation and example are exclusively targetted to the application area and the equations are in lack of flexibility for general applications. There are a lot of assumptions made to the relations between variables, which may or may not be realistic. The reviewer suggests changing the submission to a "case report" or "concept paper". The latter is probably more suitable. Response: We agree that our approach has some limitations, but the approach was to design to analyze the reality based on the given circumstance. For instance, when there is a lack of information, estimating the value would not be possible. However, the Hamiltonian maximization approach tries us to calculate the optimal proxy on given reality. Of course, we used some assumptions but all the data we used are from literature and previous studies. And the relationship between functions and variables were assumed, but based on theories. Thus, we feel that this manuscript can be treated as an article instead of “case report”.
2. The reviewer does not understand why the Nile River was chosen as the application example? None of the authors are currently working in that area. Why don't you choose a more familiar study area so that the result can be more realistic? Response: Since authors investigated the Nile for a long time. Some of references are written and published by authors. Moreover, as we mentioned in the manuscript, the Nile is a good application to apply our approach due to its current conditions. Therefore, we feel that choosing the Nile as a case study does fit in our research.
3. Pursuant to the previous point, the study area is huge, so it is unlikely that the value for any variable will stay constant throughout the study area. If the authors cannot provide an accurate spatial distribution of all variables, some kind of error estimate for the result should be provided. The reviewer recall that Hamiltonian Monte Carlo is indeed an available technique. Please try to explore the influence of variation of variables to the result. Response: We agree that the study site is huge, but as we mentioned earlier our approach is not based on estimations. Since we mentioned in the manuscript, the available data for the Nile is partial, more recent data can increase the accuracy of the results. We are also aware of Hamiltonian Monte Carlo is available technique if the variables have distributions. As we mentioned earlier, the approach that we used was the Hamiltonian maximization. This approach is well elaborated in Solow (1986) and Berck (1971) or Chaing (1992). Among the variables used in the model, nutrient deposition and climate change impacts may have distributions, but they are also simulation results. So, we reported the results based on climate change impacts and the sensitivity analysis of nutrient deposition rate. In this sense, we included this as limitation of this research in the discussions in line 454-457 to read as follows. “Finally, although our findings rely on existing documents and previous literature, the available data for the River Nile and its watershed is partial and out of date. Recent data or science-based simulation results excluding climate change scenarios have a high probability in increasing the accuracy of the results.” Berck, P. (1976). Natural resources in a competitive economy (Doctoral dissertation, Massachusetts Institute of Technology). Solow, R. M. (1986). On the intergenerational allocation of natural resources. The Scandinavian Journal of Economics, 141-149. Alpha C. Chiang. (1992). Elements of dynamic optimization. Waveland Press. Pp. 200-264.
4. The optimization process is still vaguely described. Like the reviewer said before, a major revision to the manuscript is necessary. In addition, some of the reviewer's old questions are still not answered either in the response or in the manuscript. For example, how the control variables are defined is still absent either in the manuscript or in the response. Response: For the issues of the control variables, the control variables, E, X, beta, F1, and F2 are explained in the equation (1), (8), and (15). Those variables are the only strategic behaviors that either farmers or dam manager can choose. Of course, the social planner can choose those options too. This procedure is commonly used methodology in the economics of natural resource that was well elaborated in Solow (1986) and our previous study (reference [2]), which is now included in line 223. And more explanations in line 230-232 are rewritten to read as follows: “The first-order conditions with respect to control variables that either an individual agent or the social planner only could choose policy or strategic options (i.e. the amount of sediment removal (X), soil conservation efforts (E), fertilizer use (F1,2), and the amount of environmental flow (beta)). Therefore, the first-order conditions can be written as follows:”
Round 3
Reviewer 3 Report
The reviewer appreciates the authors' response and revision of the manuscript. As the authors agreed, the data used in the study was outdated and incomprehensive, so the reviewer had a hard time believing that the authors do work in this geographical area. Nevertheless, it is not required that the authors must acquire the most up-to-date data before filing a paper; however, the type of submission must be reconsidered. The MDPI's definition for an article is a paper that "provides a substantial amount of new information". Throughout the manuscript, the reviewer can only find a novel concept, but the Nile example does not contain good data thus the result is for reference only and cannot be trusted. Based on such observations, this paper is at best a "concept paper".
Besides, the concept is new, but it is deterministic. The authors cited several very old papers in the previous response, but none of the referenced paper was known to provide evidence that a deterministic approach is a good approach for the application of this study. This study is suffered from the issues of scarcity and spatial variation of data. Since the authors did not want to do a Monte Carlo study, the deterministic approach adopted by this manuscript can only be considered as a conceptual application at best. Without a good application example, this paper should be published as a "concept paper". Please change the submission type from "article" to "concept paper".
Author Response
The reviewer appreciates the authors' response and revision of the manuscript. As the authors agreed, the data used in the study was outdated and incomprehensive, so the reviewer had a hard time believing that the authors do work in this geographical area. Nevertheless, it is not required that the authors must acquire the most up-to-date data before filing a paper; however, the type of submission must be reconsidered. The MDPI's definition for an article is a paper that "provides a substantial amount of new information". Throughout the manuscript, the reviewer can only find a novel concept, but the Nile example does not contain good data thus the result is for reference only and cannot be trusted. Based on such observations, this paper is at best a "concept paper".
Response: Authors appreciate the reviewer’s fast response. We agreed that the data was not perfect, but our manuscript contains good Nile data and a novel concept to analyze it. Thus, it is hard for us to accept the reviewer’s suggestion.
Besides, the concept is new, but it is deterministic. The authors cited several very old papers in the previous response, but none of the referenced paper was known to provide evidence that a deterministic approach is a good approach for the application of this study. This study is suffered from the issues of scarcity and spatial variation of data. Since the authors did not want to do a Monte Carlo study, the deterministic approach adopted by this manuscript can only be considered as a conceptual application at best. Without a good application example, this paper should be published as a "concept paper". Please change the submission type from "article" to "concept paper".
Response: As the reviewer pointed out, our approach is deterministic. However, tons of articles applied this deterministic approach when there is a lack of information. The authors declined the reviewer’s suggestion of applying a Monte Carlo approach only because our approach is based on the Hamiltonian Dynamic Maximization. The reviewer suggested an inappropriate method, a Monte Carlo. We cited old papers because they are the classic and novel papers. In this regard, changing the submission type from “article” to “concept paper” is not our decision to make.
