What is the Redline Water Withdrawal for Crop Production in China?—Projection to 2030 Derived from the Past Twenty-Year Trajectory

Round 1

Reviewer 1 Report

Dear Authors,

The manuscript „What is redline water withdrawal for crop production in China? – Projection to 2030 derived from past two-decade trajectory“ by Huang and Li is devoted to the determination of the limit of water withdrawal for crop production in China for the next decade based on different scenarios but also by taking into account the part of blue and green waters. In addition, a lot of data are available in order to understand the calculation of “REWCU” in the current work. Although the work is interesting, the manuscript cannot be published in the present form. Hereafter are some comments and questions, thus helping to revise your manuscript:

• Abstract: there are too many details. I strongly recommend to shorten the abstract in order to give concise information.
• Introduction: line 56 – please define here CWP.
• Materials and methods:
  1. Lines 91 to 96: I advise to reformulate this part by introducing the concept of blue and green waters here, since the difference between “irrigated water” and “rainfalls” is introduced.
  2. Line 100: I recommend to delete the concept of IRWR and/or to introduce it later. In this work, there is too many acronyms and the reader can be quickly lost.
  3. Lines 159 to 184: this part is not essential for the rest of the manuscript. I advise to shorten this part by briefly explaining the terms Pcr, Rcr and Dcr or to put it in supplement materials.
  4. Line 185: If I understand, until this line, the concept of BAWCU was defined using Qcbw and Qcgw. But from this line 185, other definitions are introduced to explain/calculate REWCU. This should be precised before introducing contribution and depletion rates, because it would be clearer for the reader.
  5. Line 202: in eq. 11, I think the term Cir should be replaced by Cgr.
  6. Lines 214-220: This part is not clear. Please, clarify what is the definition of REWCU by giving an equation if possible (since it is based on blue and green water components). If I understand, the BAWCU cannot be taken as definition for REWCU since it does not take into account the green water.
  7. Lines 232 to 254: I recommend to put the methodology in supplement materials.
  8. Line 288: In Table 3.1, there is only information on crop specificity.
• Results and discussion:
  1. For better understand, I strongly recommend to rename this section “results and discussion”. Therefore, the section 4 can be also renamed “implications in China”.
  2. Line 324: this section only described the Fig. 3. This is “useless”. I advise to shorten this part and to introduce a discussion.
  3. Lines 351, 367 and 379: the subsection should be 3.2.1, 3.2.2 and 3.2.3, respectively.
  4. Line 350: at this stage, please, remind/explain again that the parameters such as GWCR, BWCR, GWDR, BWDR etc are necessary to define the REWCU.
  5. Line 357: the global average is a world global average?
  6. 4: please, discuss briefly the variations between the regions (instead of systematically describing the data). The Fig. 3c could be also described here.
  7. Line 392: please discuss the value of CWP and its impact on the determination of REWCU.
  8. Lines 397 to 409: this part could be place at the beginning of the “results and discussion” section. (Line 404: please also explain the green water part in the redline).
  9. Table 3.2: what are the values for “sugar crops”? In addition, put the footnote in the table caption and define what is “Mg”.
  10. Line 438: it should be “lower scenario (LS)”.
  11. Line 440: please, clarify if it is ALD or ALS?
  12. Line 468: I recommend to put the Table 3.3 in supplement materials.  

Author Response

Dear reviewer,

Thanks for your reviewing comments and we deeply appreciate your critical and constructive comments and suggestions on revising and improving our original manuscript. We have revised the manuscript as you suggested, and herein in this cover letter we will reply to each and every point you mentioned in your reviewing. We insert our responses in your original reviewing texts and all our reply texts are highlighted by italics.

Reviewer1

Dear Authors,

The manuscript „What is redline water withdrawal for crop production in China? – Projection to 2030 derived from past two-decade trajectory“ by Huang and Li is devoted to the determination of the limit of water withdrawal for crop production in China for the next decade based on different scenarios but also by taking into account the part of blue and green waters. In addition, a lot of data are available in order to understand the calculation of “REWCU” in the current work. Although the work is interesting, the manuscript cannot be published in the present form. Hereafter are some comments and questions, thus helping to revise your manuscript:

• Abstract: there are too many details. I strongly recommend to shorten the abstract in order to give concise information.

Reply:

Thanks for your suggestion and we agree with you that the original abstract is over-laden by so many figures. So, we have cut it short as you suggested and made it more readable, as can be seen in the track-change revisions. We have removed detailed figures and their appended texts, and replaced them with percentages in line 17 through line 25. What is more, we have given complete form of some abbreviation in line 29 through line 31, e.g. AWW as agricultural water withdrawal, and RETWW, redline total water withdrawal.

• Introduction: line 56 – please define here CWP.

Reply:

Thanks for your suggestion and we have defined crop water productivity here, as shown in line 62 through line 65 in the track-change revision. We have added following texts:

“Crop Water Productivity (CWP) herein in this research is defined as the economic yield of a particular crop or an aggregate of crops divided by the water depleted in producing it as measured by actual evapotranspiration. CWP has been widely used metric measure ‘crop per drop’ and it is a comprehensive reflector of diverse biophysical and management elements [9] and can be used as a reliable proxy in assessing water withdrawal requirements for crop production.”.

• Materials and methods:
1. Lines 91 to 96: I advise to reformulate this part by introducing the concept of blue and green waters here, since the difference between “irrigated water” and “rainfalls” is introduced.

Reply:

Thanks for your suggestion and we have added brief explanations and definitions on green and blue water herein to render readily understanding for audience. The added texts were shown in line 102 through line 105 in the track-change revision. Because in the immediate next paragraph, we will a through and detailed explanation on splitting blue/green water, so, we just mentioned green and blue water herein to make readers first familiarize the concept. We expect your understanding on our treatment. The added texts are as follows:

“Irrigated water is also counted as blue water and the rainfall water entering into croplands soil as green water. Hence, green water played no less important roles in crop production, not only for rain-fed system, but for irrigated system as well. The split of blue/green water will be presented in detail in the next paragraph.”

1. Line 100: I recommend to delete the concept of IRWR and/or to introduce it later. In this work, there is too many acronyms and the reader can be quickly lost.

Reply:

 Thanks for your suggestion and we have removed the abbreviation IRWR as shown in line 112 in the track-change revision. However, we kept ‘water resources’ to alert the audience the conventional references to water resource since we assumed that the audience of reading interest in our paper all know that common sense concept in water community.

1. Lines 159 to 184: this part is not essential for the rest of the manuscript. I advise to shorten this part by briefly explaining the terms Pcr, Rcr and Dcr or to put it in supplement materials.

Reply:

 Thanks for your suggestions. And to be frank, we only agree in part with your recommendations because we also worry about stuffing so many terms, concepts, and equations to our potential audience. However, we also concern about the scientific and logical coherence of introducing redline water withdrawal for crop production. But we accept your suggestion, removing equation1 through equations 12, and their associated explanations into a newly added ‘supplemental materials: methodology’. In addition, due to the removal of methods into supplemental materials, we revised the title of the section as ‘developing REWCU’ to make the section more due description, as shown in line 91 of track-change revision.

1. Line 185: If I understand, until this line, the concept of BAWCU was defined using Qcbw and Qcgw. But from this line 185, other definitions are introduced to explain/calculate REWCU. This should be precised before introducing contribution and depletion rates, because it would be clearer for the reader.

Reply:

 Thanks for your suggestion. And as you afore-suggested, we have put previous all equations into supplemental materials. And furthermore we added more detailed explanation on relationship between BAWCU and REWCU in line 221 through line 223 in the track-change revision. Hence, the audience will more readily understand it.

1. Line 202: in eq. 11, I think the term Cir should be replaced by Cgr.

Reply:

 Thanks for your correction, and we have corrected in Eq.S11 in supplemental material: methodology.

1. Lines 214-220: This part is not clear. Please, clarify what is the definition of REWCU by giving an equation if possible (since it is based on blue and green water components). If I understand, the BAWCU cannot be taken as definition for REWCU since it does not take into account the green water.

Reply:

Thanks for your suggestions, we fully understand your confusions. In short, BAWCU and its associated set of parameters offer the theoretical foundation and practical toolkit for developing REWCU. In our original manuscript when defining REWCU, we rarely mentioned BAWCU - but only once in line 216 of original manuscript- in an explicit manner, but actually we mentioned a lot on BAWCU associated parameters such as green and blue water contribution rate and depletion rate. Anyway, we have interspersed more explanatory notes on both implicit and explicit relationship between BAWCU and REWCU in line 221 through line 223 in the tack-change revision. Moreover, as you have also mentioned, our manuscript should avoid stuffing so many abbreviations to readers, so, with the same spirit in mind, and as we have already developed a dozen of equations regarding BAWCU, we decided not to give further equations on relation between BAWCU and REWCU for such treatments will involve some overlapping with already defined equation. We expect your kind understanding. And again in line 319 through 324, we make a theoretically numerical relationship between CWP and REWCU based on BAWCU-related parameters BCDR and BWDR, which can supplement the explicit description on BAWCU-REWCU relationship. The added texts are as follows:

“In essence, REWCU definition is founded upon the theoretical foundation of blue/green water split and practical toolkit offered by BAWCU and its associated set of parameters, as can be referred in methodology supplement. For instance,”

1. Lines 232 to 254: I recommend to put the methodology in supplement materials.

Reply:

 Thanks for your suggestions and we have removed them to supplemental methodology part, as shown in supplemental materials: methodology.

1. Line 288: In Table 3.1, there is only information on crop specificity.

Reply:

 Thanks for your correction and it is really a non-available specificity, we have removed the sentence in the track-change revision.

• Results and discussion:
1. For better understand, I strongly recommend to rename this section “results and discussion”. Therefore, the section 4 can be also renamed “implications in China”.

Reply:

 Thanks for your suggestions, and we have renamed both sections, as shown in line 306 and line 499, respectively.

1. Line 324: this section only described the Fig. 3. This is “useless”. I advise to shorten this part and to introduce a discussion.

Reply:

Thanks for your suggestion, and we have removed first paragraph, except that we restructure the paragraph by only preserving the head sentence of the first paragraph and moved it to the head of the second paragraph, as shown in line 368 through line 369 in the track-change revision. And in our original manuscript, the second paragraph of this section is actually devoted to the brief discussion on multiple-year BAWCU dynamics. Anyway, we have added more brief discussions on that in line 378 through line 380. The added brief discussion is as follows:

“The BAWCU composition reinforced the important role played in available water that could and would be utilized by crop production, and BAWCU dynamics revealed also the substance foundation for crop production over years in China.”

1. Lines 351, 367 and 379: the subsection should be 3.2.1, 3.2.2 and 3.2.3, respectively.

Reply:

Thanks for your corrections, and we have corrected them in line 381, line 410, line 422, respectively, as shown in track-change revision.

1. Line 350: at this stage, please, remind/explain again that the parameters such as GWCR, BWCR, GWDR, BWDR etc are necessary to define the REWCU.

Reply:

Thanks for your reminding, and we have added a reminding sentence to stress the relationship between BAWCU-associated parameters with REWCU, as shown in line 382 through line 384 in the track-change revision. The added texts are as follows:

“In this and next subsection, contribution and depletion rates of green/blue water will be presented and discussed since they are BAWCU-associated parameters that are keys to defining REWCU.”

1. Line 357: the global average is a world global average?

Reply:

Yes, it is. We have added a few words to make it more explicitly referring to world average, as shown in line 370 in the track-change revision. The added texts are:

“for all countries in the world.”

1. 4: please, discuss briefly the variations between the regions (instead of systematically describing the data). The Fig. 3c could be also described here.

Reply:

Thanks for your suggestion, and we have added brief discussions on regional variations in line xxx through line xxx in the trach-change revision. The added texts are as follows:

“As compared to green/blue composition in BAWCU of 6:4, the blue and green water contribution rate is 7:3, which is consistent with the potential water available for crop use. In addition, regional variations in GWCR and BWCR also reflect regional variations in green/blue water split in BAWCU, that is: the higher the green water in BAWCU is, the higher the GWCR is (Figure 3a, and Figure 4. For those provinces with BWCR exceeding GWCR, three categories might be roughly identified. The first category belongs to extreme dry climatic zones, such as Xinjiang and Ningxia; the second belongs to main grain productions provinces, such as Jiangsu; the third belongs to developed metropolitan crop production type with developed irrigation system, such as Shanghai, Tianjin, and Beijing (Figure 4). Nevertheless, the overall pattern of Chinese GWCR and BWCR is that green water contributed more to crop production than blue water.”

1. Line 392: please discuss the value of CWP and its impact on the determination of REWCU.

Reply: Thanks for your suggestion, and we have added additional texts to explicitly explain relationship between CWP and REWCU in line 319 through line 324 in the track-change revision. The added texts are as follows:

“More explicitly, total water consumption under a given amount of crop outputs can be obtained by inverting the value of CWP. And then, the water consumption that is derived from blue water can be attained by multiplying the total water consumption and BWCR, the resulting value of which is divided by BWDR and the gross blue water that will be available for crop use will be gotten. Hence, in theory, the higher the CWP is, along with the lower BWCR and higher BWDR, the lower the REWCU.”

1. Lines 397 to 409: this part could be place at the beginning of the “results and discussion” section. (Line 404: please also explain the green water part in the redline).

Reply:

Thanks for your suggestion, and we have moved the part to the head of ‘results and discussion”, as shown in line 307 through line 326. We also added a sentence to explain why the present REWCU only confined to blue water part, and green water part will be treated in subsequent studies. The added texts on green water part of REWCU are as follows:

“In addition, the green water part of a more generalized REWCU will be touched upon in future studies for its complexity due to its reliance on rainfall patterns and cropland distribution.”

1. Table 3.2: what are the values for “sugar crops”? In addition, put the footnote in the table caption and define what is “Mg”.

Reply:

Thanks for your suggestion. Values for sugar crop are non-available and we have specified them in the table, as shown in the track-change revision. Also, we appended conversion between Mg and g in footnote of the table. Both revisions are shown in Table 3.2 and line 480, respectively.

1. Line 438: it should be “lower scenario (LS)”.

Reply:

Thanks for your correction, we have corrected it, as shown in line 482 in the track-change revision.

1. Line 440: please, clarify if it is ALD or ALS?

Reply:

It should be ALH. We have corrected in all cases, as shown in line 511, line 513 in the track-change revision.

1. Line 468: I recommend to put the Table 3.3 in supplement materials.  

Reply:

Thanks for your suggestion, and we have removed it to supplement materials: table.

Reviewer 2 Report

This article brought up the trajectory of minimal or red-line water withdrawal requirements for China’s crop production by year 2030. This study developed an inverse inference method to assess irrigation requirements for crop production. This is a well-written manuscript and encompasses all the necessary parameters. Please check if all the abbreviations are defined at their first place in the manuscript. In line 28, please define AWW. Overall in my opinion, this article is fit for publication in its present form.

Author Response

Dear reviewer,

Thanks for your positive comments on the original manuscript, and we have revise it as you suggested.

Reviewer 2

Comments and Suggestions for Authors

This article brought up the trajectory of minimal or red-line water withdrawal requirements for China’s crop production by year 2030. This study developed an inverse inference method to assess irrigation requirements for crop production. This is a well-written manuscript and encompasses all the necessary parameters. Please check if all the abbreviations are defined at their first place in the manuscript. In line 28, please define AWW. Overall in my opinion, this article is fit for publication in its present form.

Reply: Yes, we have specified AWW in its complete form, as shown in line 29 through line 30 in the track-change revision.