Impacts of Human Activities on the Variations in Terrestrial Water Storage of the Aral Sea Basin

Round 1

Reviewer 1 Report

The paper is well organized and well written. The figures and table are clear and represent the authors work well. I recommend that the conclusions section should include bullets summarizing the conclusions.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Authors,

I read your manuscript carefully and I realized that you made a great job. Your manuscript is well organized and well written. My very minor concern is dedicated to Introduction. Please refer to the following current studies:

Tangdamrongsub N, Šprlák M (2021) The Assessment of Hydrologic- and Flood-Induced Land Deformation in Data-Sparse Regions Using GRACE/GRACE-FO Data Assimilation. Remote Sensing, 13(2), 235

Yin W, Li T, Zheng W, Hu L, Han S-C, Tangdamrongsub N, Šprlák M, Huang Z (2020) Improving Regional Groundwater Storage Estimates from GRACE and Global Hydrological Models over Tasmania, Australia. Hydrogeology Journal, 28(5), pp. 1809-182

Ghobadi-Far K, Šprlák M, Han S-C (2019) Determination of Ellipsoidal Surface Mass Change from GRACE Time-Variable Gravity Data. Geophysical Journal International, 219(1), pp. 248-259

Tangdamrongsub N, Han S-C, Jasinski MF, Šprlák M (2019) Quantifying Water Storage Change and Land Subsidence Induced by Reservoir Impoundment Using GRACE, Landsat, and GPS Data. Remote Sensing of Environment, 233, 111385

p. 5, l. 146 Laster - Laser

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Review: Impacts of human activities on the variations in terrestrial water storage of the Aral Sea Basin

I have read the manuscript entitled “Impacts of human activities on the variations in terrestrial water storage of the Aral Sea Basin”, written by Yang and coauthors, proposed for publication in Remote Sensing. The papers discussed changes in TWS (Total Water Storage) in the Aral sea basin between 2002 and 2017, using GRACE-SH coefficient data and GLDAS Noah LSM L4 simulations. The objectives of the paper are to (1) asses annual and seasonal variations in TWS and (2) quantify human induced changes. I think that the topic presented and the research questions addressed are highly relevant, but could be presented in a more convincing manner. I think that there are several opportunities for the authors to improve the readability and scientific quality of their manuscript, which I will discuss in detail in the following.     

Main Comments:     

1) Better explanation how the human influence is assessed! The main topic of the manuscript is the identification of hydrological impacts of human activities in the basin. The way the authors have done this remained, however throughout the manuscript unclear. The only clearer explanation that I found comes in section 4.2.2, which is too late.

1a) The main thing that I found unclear in the manuscript was how the authors calculated the impact of humans in the Aral basin. In the beginning, I got the feeling that the difference between the modelled TWSA and the measured TWSA described the human influence on the system. The modelled TWSA, however did not include the entire surface  water component of the TWS – surface water storage components and groundwater are mostly absent in Table 1 (except perhaps for snow depth). This means that the difference in modelled and measured TWSA also includes the natural surface and groundwater and not only human components are included in this difference. The fact that the authors did it like this is also mentioned in lines 197 – 199).            
1b) Later in the manuscript this is somehow acknowledged, see e.g. line 320 – 324. Then, they state that the difference in modelled ET and ET obtained from GRACE can explain human-induced ET differences. This, however, comes with the assumption that the ET from Noah is accurate and not in any way under-/overestimated.          
1c) I think that the component change assessment is very interesting – Table 4. I do not see this as a human influence quantification per se, as this could also be caused by different climate conditions (which might partly of course also be human induced). I suggest to add this as a separate objective for this paper.  

2) I think that the written text in the manuscript still needs to be improved. I have tried to address several example cases that I have found in the text and listed them in “Details”. These might, however not include all cases. I therefore suggest the authors to again check the written text in the entire manuscript for any misleading sentences/ sentences that are not detailed/ precise enough, and grammar/ spelling issues.       
             
3) I generally found it misleading that an abbreviation for the Aral Sea Basin (here ASB) was used and would suggest the authors to stick with the full name of the region. This especially is the case for the abstract. I, however, think that it would generally make the manuscript easier to read -  also for the sake of people that might not read the entire manuscript.      
           
4) In the manuscript, the authors sometimes use TWS and sometimes TWSA. While reading, I got the feeling that in some cases the use of TWS/ TWSA was not always accurate. I suggest the authors to check the manuscript and consider rephrasing sentences where TWS/TWSA is inaccurate.
           
5) It would be great if some assumptions that are behind the setup of this study would be written out. See e.g. Line 69-70 “…the comparison of TWSA derived from GRACE and land surface models can indirectly evaluate the human water withdrawal in the region”.  There are several assumptions behind the possibility to do so. I think it would be worthwhile if some of these assumptions and perhaps also the limitations are more clearly discussed in the manuscript.

6) At the end of the introduction, the objectives are explained (Line 73 -77). Besides that I would recommend rewriting this sentence into two sentences (both containing one objective), I did not entirely get the second objective and how this is done? How is the effects of humans calculated with the GRACE and GLDAS data products? I recommend the authors to more clearly formulate this objective and more clearly explain how this is done.       

7) I think that Figure 2 needs to be improved. First of all, the quality (text x axis and legend) on the provided MPI pdf is not very high - I would recommend improving this. Moreover, I think the figure is more readable if the y axis presents the years (2002 - 2017) and the bars are colored according to available (one color) or not available (2nd color). This way it is super clear in which year, which month was missing etc. In the current version, some similar colors occur twice and it is much more complicated to read the graph and figure out where the data gaps are.         

8) I did not entirely understand the choice for the GLDAS Noah model, and the choice of the variables used to calculate TWS. IT would be great if the authors could elaborate in the text on the reason for choosing the Noah surface model. This is important, because GLDAS offers a lot of choice! I also do not understand the choice for the GLDAS variables that were used in this study to calculate TWS. The variables that are presented here do not include a lot of surface and groundwater components (little to none). This goes back to comment 1: Why was the choice made to not include simulated groundwater and surface water levels that might represent the natural conditions (no human extraction)?    

9) In several parts of the methodology, the reason for introducing a topic is not clear. For example, in line 177 GRACE errors are introduced. It is however not clear for what purpose these errors are calculated/ evaluated. For the sake of understanding/ readability, the authors should include such information at the beginning of the section/ paragraph!
Another example are line 212 – 215:”Since ET only simulates ET under …ET grace represents total ET”. I do not understand what the authors mean here. They should further explain what other human induced ET component they refer to. This is currently only mentioned in section 4.2.2., which comes, according to my opinion, way too late.            

10) Everywhere were “ temporal variations are presented, authors should mention how they have dealt with the spatial component. For example “4.1.1.1 – Temporal variations in TWS from GRACE” – Is the monthly value average over the entire basin? I assume it is, but authors need to write this in the manuscript to avoid such questions.        

11) It would be highly beneficial to have the precipitation data also plotted in Figure 4 and 6. This helps to better interpret the inter-annual and intra-annual variability.  


Details:          

1) Line 14 – 17: “ … using Gravity Recovery and Climate … (GLDAS) model”. I recommend the authors to rephrase this sentence. You did not use the model itself, but certain simulation data/ model output – be more precise here!        

2) Line 17 – 18: “The impacts of human … and water balance. The use of “perspectives” in this sentence is not correct and misleading. I recommend the authors to rephrase this sentence. This wording is used several other times in the introduction – it is recommended that the authors also rephrase other sentences where this is the case.            

3) Line 18 – 21: “ The results indicate … mm/year).” I highly recommend the authors to rephrase to avoid confusion. A decline in total water storage anomalies suggests here that the total water storage anomalies are getting smaller (all values get closer to 0). I think the authors try to state that the total water storage anomalies are becoming more “negative” with time.

4) Line 24-25:” Evapotranspiration (ET) played …water balance”. In this case it is not clear how ET played a dominant role in the depletion of TWS – please elaborate a little on this please.            

5) Line 33 – 34: “As water is much scarce in arid regions…” Incorrect wording, please consider rephrasing.

6) Line 48 – 50: ”Traditional site observations… is no exception”.  In this case the authors need to explain what site observations are meant here. I think there are indeed several hydrological observations that provide point information (e.g. certain groundwater and soil moisture measurements) , but I think this is definitely not the case for all hydrological measurements! The way these sentences are written, sounds like the authors state that there is no data transparency and no accessibility, which is NOT ALWAYS true. I would add a word like OFTEN or similar to avoid such a statement. The way these sentences are written, also sound like there is no data transparency and no accessibility, which is NOT ALWAYS true. I would add a word like OFTEN or similar to avoid such a statement.     

7) Line 56 – 57: “It has already … etc.” Consider rephrasing.         

8) Line 65 – 66: “… and they often lack … water and groundwater [6,29].” Please rephrase. Water and groundwater are not processes! Only the movement of water would be a process.

9) Line 67: “ … is less enough to be neglected”. Consider rephrasing.       

10) Line 84 – 86: “The main water resource in this … river flow [9].” Consider rephrasing.

11) The text in the caption of Figure 1 should be rephrased.

12) Line 94 – 95: “…and cold and dry in winter.” This part does not fit with the rest of the sentence. Cold and dry what? Consider rewriting.         
13) Line 99: “Due to the severe drought…”. Here it is unclear which drought is referred to. Or are the authors referring to the arid conditions in this region?           
           
14) Line 151 – 153:”The comparison of … (Figure 3d, e, and f).” Please write down why this approach effectively represents the variability of TWS? Based on what measures is this statement made? How did the authors decide on what is “best/ effective”?     

15) Line 168: Here, a scaling factor is introduced. I was thinking that this might affect the absolute difference between the modelled TWS and GRACE TWS? Does this affect the “human influence” that is quantified here? It would be great if the authors could elaborate on this.

16) Line 233 “… which means that total water consumption was much larger…”. This is not the only explanation for the observed data, but one potential explanation. Authors should consider rewriting to avoid too “harsh” causality statements that cannot be proven.           

17) “The variation in trend …”. I like that the authors compare their results with other papers. I, at the same time, wish that the author also provide a quantitative comparison here – to give the reader a clearer image of how similar the trends are (without having to read the other publication(s)).

18) Line 277 . 278: “ Presumable, the reduction in TWS…plains.” I do not understand/ agree with this statement. How is the downstream area expected to have higher water storages if less water is stored in the upstream area? This is not necessary a consequence! If less water is moving through the stream upstream, less water will end up downstream. It would even be possible that the opposite is true for nested catchments – if less water from upstream is delivered, the downstream area might even have a more severe effect (more extraction downstream + less incoming Q from upstream).     

19) Line 299- 300: “… soil moisture anomalies increased…”. If soil moisture accounts for 98.37% of the TWS, why is the rate then negative - closer to snow water equivalent! I propose to put the contributions of all components in Table 3 as well.      

20) Line 417 – 424: “The spatial heterogeneity … for a greater one”. This sentence is way too long! Consider rewriting!

           

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

I think the authors have put a lot of time and effort in addressing the comments/ suggestions. I think the quality of the manuscript has improved a lot and think that the manuscript is ready for publication in its current form.