Streamflow Decline in the Yellow River along with Socioeconomic Development: Past and Future

Round 1

Reviewer 1 Report

Dear Authors

Congratulations on a very interesting and relevant study.

I have now read it, and the only comment I would like you to consider is the lack of a section with recommendations. After going through your quantitative evaluation of the different dimensions that may impact on the reduction of the YR streamflow, I was expecting to see some recommended measures or ideas on how to address ecah of those aspects. 

There are 2 or 3 comments I made regarding what I found less justified in a few of the quantitative estimatiosn, so I attach the pdf with my notes to support your revision.

Good luck with your publication.

Best regards,

The reviewer

Comments for author File: Comments.pdf

Author Response

Review 1

In Review 1, we found 8 highlights made by the reviewer. 4 of them have comments.

Review highlight in Line 321: More than 3,000 reservoirs have been constructed in the YRB since the 1950s (Dai et al. 2009)

Author response: We guess that the reviewer wants us to check the correctness of the highlighted sentence. We have checked this sentence and found no error. This information is cited from the Table 3 by Dai et al (2009).

Review highlight in Lines 345-346: We therefore roughly estimate that reservoir-increased evaporation and water impoundment together explain approximately 5% of the decreased streamflow at Lijin from 1957 to 2016.

Reviewer’s comment: “This is a very important component of the impact on the streamflow. How do you base and justify this 5% estimation?”

Author response: In our revision, we have added explanation of the reservoir impact on streamflow and change the “5%” to 6%: “For example, net reservoir water impoundment in the YRB showed an increasing trend (Table S3). Without the changes in net reservoir water impoundment (Table S3), the decreasing rate of linear trend in streamflow at Lijin from 1957 to 2016 would be 0.6617 km3/yr, or 0.0144 km3/yr lower than the decreasing rate of linear trend in streamflow measured at Lijin from 1957 to 2016 (0.6761 km3/yr, Table S2). That is, the increasing trend in net reservoir water impoundment resulted in a cumulative streamflow reduction by 0.86 km3 over the past 60 years, which was responsible for 2.2 % of the trend-based cumulative decrease in streamflow at Lijin from 1957 to 2016 (39 km3/yr). Considering that the reservoir-increased evaporation in the YRB was responsible for 3.5 % of the trend-based cumulative decrease in streamflow at Lijin from 1957 to 2016, we roughly estimate that reservoir-increased evaporation and water impoundment together explain approximately 6% of the decreased streamflow at Lijin from 1957 to 2016.” See Lines 368-376. In the Abstract, we also have changed the reservoir impact on streamflow from “5%” to 6%. See line 27.  

 

Review highlight in Line 358： …, we attribute the remaining 6% of the decreased streamflow at Lijin mainly to APG.

Reviewer’s comment: “These estimations should be better explained.”

Author response: We have added explanation for the estimation of APG contribution to the streamflow decline: “Because the potential evaporation in the YRB has not shown any increasing trend over the past decades (Liu et al. 2013), evaporation change is unlikely to be responsible for the streamflow decline at Lijin. Considering that water consumption, precipitation decrease and reservoir construction contributed to 76%, 13% and 6% of the streamflow decline at Lijin, respectively, we attribute the remaining 5% of the decreased streamflow at Lijin mainly to APG.” See Lines 391-396.

 

Review highlight in Lines 410-412：However, the temporal trends in precipitation are non-significant (Table S2). Thus, no firm conclusion regarding the impact of precipitation on streamflow can be made, and, therefore further studies are needed.

Author response: We guess that the reviewer wants us to check the necessity of these two sentences. In our revision, we found that these two sentences are postiche and unnecessary. Thus, we have deleted them. See Line 470.

 

Review highlight in Lines 445-447：These programmes will further decrease streamflow. By 2030, there will likely be insufficient water to satisfy the water requirements and therefore result in a water shortage.

Author response: We guess that the reviewer wants us to improve our writing in these sentences. We have revised the two sentences to be: “These programmes presumedly will lead to further decrease in streamflow in the YR. By 2030, the streamflow in the lower reaches of the YR will most likely be insufficient to satisfy the water requirements.” See Lines 503-505.

 

Review highlight in Lines 496-497：…unless effective countermeasures are taken.

Reviewer’s comment: “Maybe be you could identify some of these measures.” 

Author response: Three measures are suggested in the following sentences. We have revised the addresses to be: “…unless effective countermeasures against water shortage are taken. The countermeasures could include (1) improving the efficiency of water usage especially in agriculture, (2) water diversion (e.g., 5–10 km3/yr) from the neighbouring Yangtze River where water resources are relatively abundant (Yang et al. 2010), and (3) artificially increasing precipitation within the YRB (Li 2019). See Lines 555-558.

 

Review highlight in Lines 496-497：…The streamflow decline was mainly (87%) attributed to rapid socioeconomic development which significantly increased water consumption,…

Author response: We guess that the reviewer wants us to improve the description of this sentence. We have revised the sentence to be “The streamflow decline was mainly (87%) attributed to rapid socioeconomic development which significantly increased water retention and water consumption within the drainage basin”. See Lines 610-612.

 

Review highlight in Lines 559-561：Our results suggest that streamflow in semiarid basins is highly vulnerable to human impacts and that streamflow decline would in turn hinder further socioeconomic development and endanger river-sea ecosystems also.

Reviewer’s comment: “It would be interesting to follow your conclusions with some recommendations, regarding the specific weight and impact of each analysed dimension to the streamflow decrease”

Author response: We have added a sentence in the end of Conclusions section: “We appeal for in-depth studies on future streamflow trends under human and climatic impacts and for river-sea integrated and socioeconomics-ecosystem integrated water resources management within semiarid basins in North China and worldwide.” See Lines 625-628.    

Dear Reviewer 1, Thank you very much for your helpful comments!

 

Author Response File: Author Response.docx

Reviewer 2 Report

find attached

Comments for author File: Comments.pdf

Author Response

Review 2

GENERAL COMMENTS

The paper aims to deepen research on the status and trends of the of the Yellow River streamflow, that plays a key role in the socio-economic development of the country. The analysis focuses on the causes of the loss of the streamflow, evaluating the weights of the main pressure drivers (water consumption, compression of resources, revegetation, construction of reservoirs). As stated by the authors, other studies have already examined the contribution of climatic and anthropogenic factors on the reduction of the Yellow River streamflow. The paper, in addition to providing further results on the subject, aims to enrich the degree of knowledge on the state of the outflow of the Yellow River, also predicting future trends, taking a step forward compared to the state of knowledge of the topic. The object of the analysis is therefore scientifically relevant, since it aims to fill the gaps in the current level of knowledge. The results are clear and well represented in the figures and tables. However, the methodology that led to the results is not completely clear.

SPECIFIC OBSERVATION (Author’s note: Probably because the manuscript version seen by Reviewer 2 is different from that seen by Reviewer 1 and that we can download from the submission system, the line numbers after Line 123 are dislocated.)

Lines 52-53 "As the amount of water (as well as sediment, nutrients, etc.) passing through a river section in a unit time, streamflow is the most important natural river process". I would suggest to review the phrase.

Author response: We have rephrased this sentence to be: “Streamflow is the amount of water passing through a river section in a unit time.” See Lines 55-56.    

Lines 123-135. The difference between the method used in the paper and the traditional one is not clear.

Author response: The line numbers are probably Lines 121-133. We have added description of the difference between our method and the traditional one: “In the traditional method, the population, grain yield and GDP of the administrative regions which stretch across the watershed boundaries are completely included as the data in the basin. In other words, some areas beyond the watersheds are included as parts of the river basin in the traditional method. In comparison, only areas within the watersheds are included as portions of the river basin in our method.” See Lines 129-134.

Line 154. The specification of the test the regression model and the values used (also

through an Annex section) would make the analysis clearer.

Author response: The line number is probably Line 153 that represents the paragraph below this subtitle. We have added specific description of the regression model and the values used: “…using the best temporal regression trend equations of annual streamflow in Table S2. For example, the best temporal regression trend equation of annual streamflow at Lijin in is QM = –1344ln(Y) + 10235.9 (R₂ = 0.656, p < 0.0001) where Y represents calendar year and QM represents the streamflow (km3/yr) measured at Lijin in the corresponding calendar year. Based on this equation, the QM 1957 and QM 2016 were calculated to be 49.5 km3/yr and 9.6 km3/yr, respectively…..”. See Lines 160-174.  

Line 172. R2 = 65 should be R2 = 0.65

Author response: We found “R² = 65” only in Line 166. We have changed it to “R² = 0.65”. See Line 178.

Line 234. I would suggest to recall and specify the two methods with reference to Table S2, also with reference to the methodological section.

Author response: We could not find any information on “the two methods” around Line 234. We found “the two methods” only in Line 213. We have added a few of sentences to recall and specify the two methods with reference to Table S2 and the methodological section: “These inconsistent results are attributed to differences in calculation between the two methods. Specifically, in the baseline period method, the average annual streamflow values during the earliest and latest decades are calculated and compared. In comparison, in the statistical trend method, regression trends based on the time series of annual streamflow over the 60 years are established and employed to predict the streamflow values in the earliest and latest annual years (see the methodological section 2.2 and Table S2).” See Lines 231-236.

Line 313-314. It would be appropriate to clarify the aggregation of the reaches of the river, specifying which gauging stations belong to upper, middle and lower reaches.

Author response: In the manuscript version we can see, the words “upper, middle and lower reaches” occur in Lines 292-293. We have added the information of the gauging stations: “ Spatially, approximately 40% of the water consumption occurred in the upper reaches (above the Toudaoguai Station), 30% in the middle reaches (between the Toudaoguai and Huayuankou Stations), and 30% in the lower reaches (below the Huayuankou Station). See lines 314-316.

Line 328. The reference to Figure 3a suggests that a relationship between the irrigated area and the population is represented, while Figure 3a only contains data on the population.

Author response: In the manuscript version we can see, the line number is probably Line 303. The relevant sentence mentioned by the reviewer should be: “Based on the regression equation between irrigation area and population, the irrigation area would have reached 57´103 km² by 2016 when the population was 107´10⁶ people (Fig. 3A).” We accept that our reference to Fig. 3 in this sentence is misleading. Our reference to Fig. 3 was originally for “by 2016 when the population was 107´10⁶ people”, but the sentence ended with (Fig. 3A) misleads to “the regression equation between irrigation area and population”. In order to avoid this misleading, we deleted the reference to Fig. 3 in the sentence. See Line 326.  

Line 422. Figure E should be figure 5F.

Author response: We have changed “Fig. E” to “Fig. 7E”. See Line 449.

Lines 454-455. Table S6 should be Table S5.

Author response: We have changed “Table S6” to “Table S5”. See Line 458.

Paragraph 3.2 The problem of the non-significance of temporal precipitation trends is not mentioned.

Author response: We have added two sentences to mention this problem: “It is necessary to indicate that the temporal regression trends in precipitation mentioned above are all nonsignificant in statistics (Table S2), and that their applications are less reliable than significant trends if there are. Nevertheless, we suppose that the utilization of these nonsignificant trends is better than no trend can be used in identifying the impact of precipitation change on streamflow.” See Lines 262-266.

Table 1. There is a misprint in "Tannaihai"

Author response: We have changed "Tannaihai" to ‘Tangnaihai” in Table 1.

 Table 1. I would suggest to review the% changes. In particular, several results have a wrong sign (e.g. % change of precipitation water in Toudaoguai and % change of streamflow in Lanzhou). Some values do not correspond to the calculations made (e.g. %change of precipitation in Lanzhaou and Toudaoguai and %change of precipitation in Lanzhou); some values are imprecise for decimal places (e.g. change in rainfall% and change in runoff% in Tangnaihai).

Author response: We have checked the calculation of the values and corrected the wrong signs and numbers in Table 1.

Table S1. It is not clear whether the data sources refer only to the values of the Yellow River Basin or even to the global scale. Otherwise the data source on a global scale is missing.

Author response: We have made changes to separately show the data sources for the Yellow River Basin and the global scale. See Table S1.

 Figure 2. The results obtained from the best regressions do not correspond to those reported in the text (lines 214-217). In particular, figure 2a shows a value of Qm obtained from a regression with the highest p-value of those reported in table S2 (instead of the lowest that leads to select Qm = -14% correctly reported in the text).

Author response: We apologize for our mistake! We had submitted an old version of Fig. 2. In submitting our revision, we will upload the correct Figure which corresponds to Table S2 and the text.

Dear Reviewer 2, Thank you very much for your helpful comments!

 

Author Response File: Author Response.docx

Reviewer 3 Report

In my opinion the manuscript seems suitable to be published in the Water after suggested changes (See Information for Authors).

Comments

1. In Abstract: please change the sentence: “We appeal…”. The abstract should contain the main conclusions, not appeals.
2. It is also very important to identify causes of water shortages at local scale (line 44). Sometimes even more important than at regional or global scale. There are e.g. areas of local water shortages resulting from the existence of a mine… In general, the problem discussed in the article is very complex and it is difficult to expect convincing results. The Yellow River basin is bigger than the largest surface country in the  European Union… In my opinion, it is difficult to draw valuable conclusions for such an area based on only 7 gauging stations…
3. I suggest to add a diagram showing and describing the methodology.
4. Land use changes in analysed years as an important factor should be described more in detail.
5. In the context of retention reservoirs, it should be remembered that they should contribute to maintaining an inviolable flow throughout the hydrological year.
6. If we think about water management, we have to remember that the demand for water (especially in agriculture) is also seasonal.
7. The Introduction sections lacks references to the problem of water shortages in other major rivers in the world.
8. Irrigations area should be showed in a map.
9. For future scenarios, it would be worth considering more efficient water management in agriculture.
10. The authors should not use CNY… in international paper (I suggest USD).
11. The work is interesting, but from the hydrological point of view it contains too many assumptions and generalizations.
12. I suggest, due to the wider socio-economic context of the manuscript and vague conclusions (a form of appeal), its publication in the journal Sustainability.

Author Response

Reviewer 3

In my opinion the manuscript seems suitable to be published in the Water after suggested changes (See Information for Authors).

Comments

1. In Abstract: please change the sentence: “We appeal…”. The abstract should contain the main conclusions, not appeals.

Author response: We have deleted the sentence beginning with “We appeal…” in the Abstract, because our main conclusions are addressed before this deleted sentence. See Line 32.

2. It is also very important to identify causes of water shortages at local scale (line 44). Sometimes even more important than at regional or global scale. There are e.g. areas of local water shortages resulting from the existence of a mine… In general, the problem discussed in the article is very complex and it is difficult to expect convincing results. The Yellow River basin is bigger than the largest surface country in the European Union… In my opinion, it is difficult to draw valuable conclusions for such an area based on only 7 gauging stations…

Author response: We agree on that sometimes water shortages at local scale are even more important than at regional or global scale. In our original manuscript, local scale was included by regional scale. Perhaps this inclusion is inappropriate. In our revision, we changed “at both global and regional scales” to “at global, regional and local scales”. See Line 47.

As for the last sentence in Comment 2, we agree that the more the gauging stations, the better the conclusion. Actually, data on precipitation, temperature and pan evaporation from 82 gauging stations were employed in this study. Gauging of streamflow is much more difficult than gauging of precipitation, temperature and pan evaporation. Although streamflow data from only 7 gauging stations were used in this study, these stations are located in different reaches of the mainstem of the Yellow River. Most importantly, because of the characteristics of drainage area, streamflow changes at a station reflect the comprehensive impact from the catchment above station. For example, streamflow changes at the Lijin Station reflect the comprehensive impact from nature and anthropogenic drivers in the entire basin above the tidal limit. In fact, there are many examples of study on streamflow change in large rivers which are based on data from a gauging station close to the river moth. In this study, even though data from only the 7 stations are not perfect, that are what we can collect, and that are valuable and efficient for us to examine the anthropogenic and climatic impacts on streamflow over the past 60 years.     

3. I suggest to add a diagram showing and describing the methodology.

Author response: We have added a diagram to show and describe the methodology of this study. See Figure 2.

4. Land use changes in analysed years as an important factor should be described more in detail.

Author response: We have added a paragraph to discuss relationship between the land use/cover changes and the streamflow decline. See Lines 397-419.

5. In the context of retention reservoirs, it should be remembered that they should contribute to maintaining an inviolable flow throughout the hydrological year.

Author response: We have added a sentence to address the role of reservoirs in maintaining an inviolable flow throughout the hydrological year. See Lines 379-382.

8. If we think about water management, we have to remember that the demand for water (especially in agriculture) is also seasonal.
9. Author response: We have added a sentence to address the seasonal variability of water demand and its potential relation to water management. See Lines 600-603.
10. The Introduction sections lacks references to the problem of water shortages in other major rivers in the world.

Author response: We have added three sentences to address examples of water shortage in other major rivers. See Lines 39-43.

9. Irrigations area should be showed in a map.

Author response: It is difficult for us to show the spatial distribution of the irrigation area in a map, because this area was changed in the history and detailed data of its distribution are unavailable. You may suggest that we show the historical increases in the catchment-wide irrigation area. To do this, we have added a histogram. See Figure 5.   

10. For future scenarios, it would be worth considering more efficient water management in agriculture.

Author response: We accept this comment. Because the time period given by the editor for our revision is short (12 days even after we applied for a delay) and revision suggested by the three reviewers is large, we could have added a few sentences to simply address the influence of a future scenario of more efficient water management (especially in agriculture) on the future streamflow trend. See Lines 556 and 559-563.

11. The authors should not use CNY… in international paper (I suggest USD).

Author response: We have changed CNY to USD. See Lines 599-560.

12. The work is interesting, but from the hydrological point of view it contains too many assumptions and generalizations.

Author response: Thank you for your comment! Because of the urgent deadline given for us to submit our revision and because this comment is generalized, it is difficult for us to make specific revision. However, after our revision by following so many comments and suggestions of the three reviewers, the flaw indicated by you in this comment has been improved. 

13. I suggest, due to the wider socio-economic context of the manuscript and vague conclusions (a form of appeal), its publication in the journal Sustainability.

Author response: Both Water and Sustainability are good journals. If the editor of water agrees on this suggestion and if the editor of Sustainability accepts this revised manuscript, we would agree. Otherwise, we insist on publication in Water.  

Dear Reviewer 3, Thank you very much for your helpful comments!

Author Response File: Author Response.docx