Water Allocation, Return Flows, and Economic Value in Water-Scarce Environments: Results from a Coupled Natural-Human System Model

Round 1

Reviewer 1 Report

1. There are two branches of industrial return flow in Figure 1B (flesh-color arrow and purple arrow), but the flesh-color arrow has been annotated as agricultural return flow, it is inevitably confusing to appear in industrial return flow again.

2. Lines 129~130,“The absolute magnitude of peak demand values are of no significance because the system dynamics are driven by the relative values of each of these parameters.”,The authors are recommended to explain the principle in depth.

3. Is the WTP ratio in Table 1 based on actual conditions？Is it significantly different from the actual industrial WTP?

4. What is the actual percentage of agricultural return flow, whether it is similar to the percentage of return flow in the experimental design in Table 1, and whether high return flow scenarios such as 45% and 60% can be realized at present, the application of the model needs to be considered.

5. Figure 2: Is agriculture use (AF) defined as horizontal axes of all the graphics too one-sided? The curves of industry and total water use also share the same horizontal axis, which is easy to cause ambiguity. This problem also appears in the subsequent figure.This part needs to be revised slightly considering above comments, and make it easier and clearer to understand the information the authors want to present .

6. There are deviations in the size and position of the three figures in Figure 4, which should be as uniform as possible, so please check it carefully.

7. Conclusions are not just about summarizing the key results obtained, in which more quantified and useful information should be provided.

8. Authors are asked to double-check the grammatical issues throughout the text to ensure that there are no grammatical or word errors.

Author Response

 

1. There are two branches of industrial return flow in Figure 1B (flesh-color arrow and purple arrow), but the flesh-color arrow has been annotated as agricultural return flow, it is inevitably confusing to appear in industrial return flow again.
   
   We appreciate the reviewer pointing out that this figure needs clarification. The purpose of this figure is to trace the fate of agricultural return flows through the entire system. Thus, the flesh-colored arrows (or portions of arrows) represent flows that were once used for agriculture and have been recycled through the river system. To clarify this purpose, we have modified this figure and the legend and added clarification to both the figure caption and the text. We believe it should now be clearer what each of the arrows represents.
   
   
2. Lines 129~130,“The absolute magnitude of peak demand values are of no significance because the system dynamics are driven by the relative values of each of these parameters.” The authors are recommended to explain the principle in depth.
   
   We thank the reviewer for pointing out this confusion. We have moved this sentence and expanded it to better explain our objectives, and to better summarize the reasons that relative values of each of these parameters are more important than absolute values.
    
3. Is the WTP ratio in Table 1 based on actual conditions? Is it significantly different from the actual industrial WTP?
   
   We have modified the text to address this question. Specifically, we have clarified that in many parts of the western United States, the embedded value for municipal and industrial water can be orders of magnitude higher than the value for agricultural water (i.e., WTP ratios can significantly exceed 4:1). However, once a value of 4:1 is reached all of the water is allocated to the industrial user regardless of how much higher the WTP ratio goes. Thus given the parameter space we are exploring there is no need to explore system dynamics with WTP ratios higher than 4:1.
   
   
4. What is the actual percentage of agricultural return flow, whether it is similar to the percentage of return flow in the experimental design in Table 1, and whether high return flow scenarios such as 45% and 60% can be realized at present, the application of the model needs to be considered.
   
   We included two references in the original paper that describe actual irrigation efficiencies for agricultural systems in the western United States. The values of 15% and 45% are reflective of those efficiencies. We have modified the text to clarify that we used the higher value of 60% primarily to explore additional system dynamics at an extreme high end of observed ranges.
   
   
5. Figure 2: Is agriculture use (AF) defined as horizontal axes of all the graphics too one-sided? The curves of industry and total water use also share the same horizontal axis, which is easy to cause ambiguity. This problem also appears in the subsequent figure. This part needs to be revised slightly considering above comments, and make it easier and clearer to understand the information the authors want to present.
   
   We thank the reviewer for noting that this needs clarification. Because of the return flows, we felt it was most straightforward to express these axes in terms of water withdrawn by the upstream user. This is because the water remaining for downstream users is a function of three factors: total water available, the amount of water withdrawn by the upstream user, and the return flow fraction. However, to clarify we have added a second set of x-axis labels to Figures 2 and 4 that explicitly show the remaining water available for industrial uses, and we have modified the figure captions where appropriate. An example of this change for Figure 2 is pasted below. We believe these changes will make the results more interpretable, per the reviewer’s comment.
   
   
   
6. There are deviations in the size and position of the three figures in Figure 4, which should be as uniform as possible, so please check it carefully.
   
   We have updated these figures so the sizes are uniform.
   
   
7. Conclusions are not just about summarizing the key results obtained, in which more quantified and useful information should be provided.
   
   We have expanded the Discussion and Conclusions section to compare our results to previous studies, and describe implications of our work for broader water conservation efforts and markets in the future.
   
   
8. Authors are asked to double-check the grammatical issues throughout the text to ensure that there are no grammatical or word errors.
   
   We have completed a more thorough review of grammar, spelling, and overall language.

Reviewer 2 Report

Abstract

The model used in this research and the data used should be presented in more detail in the abstract.

 

Introduction

It is recommended that the authors carefully review the research literature and identify the research gaps and contribution of this research.

It is better to consider a separate section for research literature.

 

Martials and method

The research method part of this study is not written very clearly, it needs to be explained in detail.

Results

The results of this study should be compared with the findings of other studies.

 

 

The policy implications and conclusion need to be more concrete.

Author Response

 

1. The model used in this research and the data used should be presented in more detail in the abstract
   
   We have edited the abstract to clarify that our model was built in the MATLAB computing environment, and that the parameter values used are abstractions of reality but are intended to represent realistic values of each parameter.
   
   
2. It is recommended that the authors carefully review the research literature and identify the research gaps and contribution of this research.
   
   We have expanded our literature review to look more deeply at other hydro-economic modeling studies and evaluate the degree to which return flows are included in those studies. We have expanded the references in our introduction to reflect these changes. We note that the Introduction section of our manuscript already included more than a dozen references that are relevant to our research.
   
   To the reviewer’s second point, the last paragraph of our introduction specifically highlights the major research gap our study seeks to fill, which is that return flows have rarely been incorporated into hydro-economic modeling studies in the past. We have also expanded the number of references cited in this part of the Introduction.
   
   
3. It is better to consider a separate section for research literature.
   
   As noted above, we included a review of relevant literature into the Introduction section of our manuscript. We followed the recommended template for the journal, which does not include a separate section for a literature review.
   
   
4. The research method part of this study is not written very clearly, it needs to be explained in detail.
   
   We have expanded the methods section of the paper significantly, to clarify how the model was developed, what it does, and how the physical and economic components of the model interact. We believe these changes address the reviewer’s concerns about clarity of methods.
   
   
5. The results of this study should be compared with the findings of other studies.
   
   We have expanded the Discussion and Conclusions section to compare our results to previous studies, and describe implications of our work for broader water conservation efforts and markets in the future.
   
   
   
6. The policy implications and conclusion need to be more concrete.
   
   We have expanded the Discussion and Conclusions section to compare our results to previous studies, and describe implications of our work for broader water conservation efforts and markets in the future.
   
   

Reviewer 3 Report

Specific Comments

1.      Keywords first letter should be capital

2.      In the introduction the author add recent references.

3.      Page number 4: Table merged with line numbers. The author should check the line numbers

4.      Figure 2: The author should mention the a,b,c in the figures.

 

5.      Section 4: The author should use Discussion and Conclusion 

Author Response

 

1. Keywords first letter should be capital
   
   We have capitalized the first letter of each keyword, as requested.
   
   
2. In the introduction the author add recent references.
   
   We have expanded the introduction both to better explain our objectives, and to increase reference to recent and past work on similar topics. We believe the expanded introduction provides better context for what this manuscript sets out to do and how it relates to previous work.
   
   
3. Page number 4: Table merged with line numbers. The author should check the line numbers
   
   We have checked and updated line numbers throughout.
   
   
4. Figure 2: The author should mention the a,b,c in the figures.
   
   We have updated the figure and caption so that it is clear which components are which.
   
   
5. Section 4: The author should use Discussion and Conclusion 
   
   We have renamed this section Discussion and Conclusions. We have also expanded this section in response to Reviewer #1, Comment #7, and Reviewer #2, Comment #6.

Round 2

Reviewer 1 Report

要求作者仔细检查整个文本中的语法问题，以确保没有语法或单词错误。

Reviewer 2 Report

I believe the manuscript has been sufficiently improved