Impact of Climate Change on the Spatio-Temporal Variation in Groundwater Storage in the Guangdong–Hong Kong–Macao Greater Bay Area
Round 1
Reviewer 1 Report
Huang et al provide an application of the use of satellite data to estimate the spatial and temporal variation of the groundwater storage in Great Bay area. I appreciate the elaborations made on the remote sensing data, but any assumption suffers the lack of a description of the geological and hydrogeological background. The results are then poorly supported by the knowledge of the groundwater dynamics. In my opinion the work maybe improved with the comments I include below, but it can not be published on Sustainability Journal. In my opinion the authors should focus on the methods and resubmit the manuscript to Remote Sensing journal (MPDI).
Comments:
Most of the references in the first sections are in Chinese. I suggest to avoid as much as possible the use of grey literature (or articles in Chinese). In literature are present many articles that may support your manuscript like 10.1016/j.horiz.2022.100042 and 10.1080/17445647.2020.1761903 (I’m not co author of any of this works). I suggest to improve and update your reference list.
Line 42 “the per capita water resources” means the used water resources or the available? In any case you should explain how it is related with the increase of the population
Line 52-54 “Groundwater is a water resource stored in the cracks…” it is true in fractured aquifers (crystalline limestone etc) characterized by secondary permeability. On the contrary in porous media (sand gravel etc) the groundwater flows thought the pores. Please check a book on the basic hydrogeological knowledge
Line 55 the GBA has a great potential for groundwater exploitation…this statement should be supported by other geological and hydrogeological data because the bibliography I checked on this area, the aquifers seems not so productive especially in the sectors where the crystalline aquitard basement crops out
2.1 Study area: this area suffer the lack of any Hydrogeological information. It’s difficult to discuss about groundwater without any background
2.3.5 26 groundwater table stations: in the figure I can recognize only 18 stations, please check
Line 156-157 before delete the outliers you checked if this data may be associated to an impulsive response in fast recharge systems (e.g. a karst aquifer)??
Line 158 – 159 the time series with more than 45% of missing data should not be taken in account because the lack of the complete monitoring of the hydrologic year may led to overestimate or underestimate the mean water table
Fig. 1 please check the zone at the elevation -111 m. Please add m a.s.l.
The monitoring data seems to be clustered. According to the hydrogeological heterogeneities why the authors did not focus only on smaller areas?
Fig 2 “the shaded areas represent grids with statistically significant trends. This issue should be discussed in the text giving a reason why we have only in these areas a trend
Line 250 absolute value relatively small: in the manuscript the authors correctly pose the accent to the presence of uncertainties in their elaborations. The authors should stated if the amount of the uncertainties has the same magnitude of the detected values and trends
Section 3.2 should be rewritten with more details
Fig 4 why are present some empty (blank) areas?
Section 3.3 the first part is not very clear. The authors should better describe how they manipulate the original data and the quality of the available datasets
Line 299 some uncertainties: how much is the magnitude of the uncertainties? May be comparable to the detected trends?
Line 301-303: the authors may made a deep research in literature to find this data. If not they should take in account to move the attention of their results from the groundwater storage to just the anomalies (then correct the title accordingly)
Figure 5: I’m not sure if the simulated and observed times series refer to a specific point (in this case insert the Id the label in Fig1.) or is it is a mean value over the study area. In case it is a mean value it seems not so relevant according to the extension of the area, the different behaviours stated in the last part of the manuscript and due to the different hydrogeological settings
Section 3.4 the results are not clearly discussed in a hydrologic/hydrogeologic point of view. The comment for the fig 6 is the same for the previous one: the graphs represent mean values? How they can be relevant at this scale?
Fig 6a represent the yearly rainfall or what? The values seem to be smaller for a year but at the same time the mean monthly rainfall may not be a useful data according the seasonal variability of the rainfall
The 3.5 section may be more relevant, but it is not clear why the authors take in account the evapotranspiration and the temperature separately. The temperature is usually a fundamental parameter for the evapotranspiration calculation. Please discuss in detail how you estimate the evapotranspiration and if these results are in agreement or not with the temperature variations
It is not clear why the evapotranspiration reaches values less than 20% in some areas even if the evapotranspiration is the main cause of water loss before the infiltration
Line 377 378 please describe it more in detail
Line 386 The significant decrease in GWS in this region was closely related to evapotranspiration. It seems not in accord with line 301 “Note that the groundwater level data obtained from the water wells needed to be multiplied by specific yields to estimate the GWS [51]. Due to unreliable specific yield data, GWSA was verified by comparing the annual variation and trends of observed and calculated data”. Please justify.
The significant decrease may be put in relationship with the anthropic withdrawals and the increase in water demand? Please discuss it
Author Response
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Author Response.pdf
Reviewer 2 Report
The study "Impact of climate change on the spatio-temporal variation of 2 groundwater storage in the Guangdong-Hong Kong-Macao 3 Greater Bay Area" by Huang et al is very interesting.
I have only minor comments as given below:
Line 38: Reference missing
Line 41: It is not clear what is meant by “productivity”….
Line 45: Is it “with” or…”from a single water source” ?
Line 46: What are the “hidden threats” ?
Line 52: “Groundwater is a water resource stored in the cracks of underground sand” Please rephrase this
Line 53: Please rephrase and give reference. Groundwater is actually accounting for around 99% of all liquid freshwater on earth…
61: What is meant by “stations” is it monitoring wells ?
Line 121/122: “The data was obtained from…” Please give more details how the data was collected, was it downloaded from a website, in what format etc.
Line 127: “2 m of air temperature”… Is air temperature 2 m above ground meant here ?
“10 m of wind speed” … Please rephrase
Line 132: Should be approximately 1 km x 1 km
Line 133: Is it 8 soil layers or 8 soil types
Line 148: “data mainly bythe”—Check spacing
“adjustment of other measurements” This is quite general here, consider deleting
Line 170: “SM” I assume SM stands for Soil Moisture has it been introduced as such before in the manuscript ?
Line 212: “ evapotranspiration was obtained by CLM5.0 simulation” – There is no measured evapotranspiration data available that can be used ?
Line 217: Please check spacing
Line 233: “The CMFD was used to force the CLM5.0” : Please rephrase this sentence
Line 256: “and a significant peak in 2013”: There is also a significant trough in 2015. What could this relate to ?
Line 265: “like the trend” I suggest to change it to “similar”as both values are not alike.
Line 267: “indicated reasonable simulated SM” : change to “indicated a reasonable simulated SM”
Line 281: “Overall, CLM5.0 could better reflect the SM changes in the GBA” …better than what ?
Line 320: “especially the leakage problem” Please describe how the “leakage problem” affects the simulation.
Line 323: “affect the availability of water infiltrates” should be “…water infiltration..”
Conclusion: Coming back to the title of the paper. The conclusion could better describe the impact of climate change on groundwater storage in the GBA. In the discussion results can be compared to other studies in the literature that investigated the impact of climate change on water resources and water quality, e.g. (https://doi.org/10.1007/s12665-020-09157-2)
The study "Impact of climate change on the spatio-temporal variation of 2 groundwater storage in the Guangdong-Hong Kong-Macao 3 Greater Bay Area" by Huang et al is very interesting.
I have only minor comments as given below:
Line 38: Reference missing
Line 41: It is not clear what is meant by “productivity”….
Line 45: Is it “with” or…”from a single water source” ?
Line 46: What are the “hidden threats” ?
Line 52: “Groundwater is a water resource stored in the cracks of underground sand” Please rephrase this
Line 53: Please rephrase and give reference. Groundwater is actually accounting for around 99% of all liquid freshwater on earth…
61: What is meant by “stations” is it monitoring wells ?
Line 121/122: “The data was obtained from…” Please give more details how the data was collected, was it downloaded from a website, in what format etc.
Line 127: “2 m of air temperature”… Is air temperature 2 m above ground meant here ?
“10 m of wind speed” … Please rephrase
Line 132: Should be approximately 1 km x 1 km
Line 133: Is it 8 soil layers or 8 soil types
Line 148: “data mainly bythe”—Check spacing
“adjustment of other measurements” This is quite general here, consider deleting
Line 170: “SM” I assume SM stands for Soil Moisture has it been introduced as such before in the manuscript ?
Line 212: “ evapotranspiration was obtained by CLM5.0 simulation” – There is no measured evapotranspiration data available that can be used ?
Line 217: Please check spacing
Line 233: “The CMFD was used to force the CLM5.0” : Please rephrase this sentence
Line 256: “and a significant peak in 2013”: There is also a significant trough in 2015. What could this relate to ?
Line 265: “like the trend” I suggest to change it to “similar”as both values are not alike.
Line 267: “indicated reasonable simulated SM” : change to “indicated a reasonable simulated SM”
Line 281: “Overall, CLM5.0 could better reflect the SM changes in the GBA” …better than what ?
Line 320: “especially the leakage problem” Please describe how the “leakage problem” affects the simulation.
Line 323: “affect the availability of water infiltrates” should be “…water infiltration..”
Conclusion: Coming back to the title of the paper. The conclusion could better describe the impact of climate change on groundwater storage in the GBA. In the discussion results can be compared to other studies in the literature that investigated the impact of climate change on water resources and water quality, e.g. (https://doi.org/10.1007/s12665-020-09157-2)
Author Response
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Author Response File: 
Author Response.docx
Reviewer 3 Report
Comments and Suggestions for Authors
1. Line 82. When an abbreviation first appears in the main text, its full name should be given. Please check it throughout the whole main text.
2. The advantages of the GRACE+CLM model used in this paper should be further illustrated by comparing with other research methods.
3. Draw a technical flowchart of the data and methods used in this MS.
4. It’s recommended to place Figure 2 in the results section.
5. The good correlation between SM simulated by CLM5.0 and SM simulated by ESA CCI does not mean that the results of CLM simulation are better.
6. The interpretation of the principle and method of CLM model to simulate the change of GWS from 2002 to 2018 is not clear enough.
7. Line 364-365. It’s recommended to explain the meaning of the contribution rate mentioned in the passage. Is it the average contribution rate or what?
8. The abstract mentions simulating GWS, but the MS simulates GWSA. What are the differences and connections between the two?
9. The multivariate linear model can only explore the linear relationship between factors and dependent variables, and it is suggested to further consider the nonlinear relationship between them.
10. It’s recommended to combine the subsurface hydrogeological conditions to analyze the spatial-temporal variation of groundwater storage. See https://doi.org/10.3390/w14101651 and https://doi.org/10.3390/w13091255
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Comments to the authors (if any)
I am writing in regard to manuscript ID sustainability- 2399344 entitled “Impact of climate change on the spatio-temporal variation of groundwater storage in the Guangdong-Hong Kong-Macao Greater Bay Area”, which was submitted to the Sustainability MDPI. After careful review, I have a major revision that I would recommend the author consider:
1- The linear trend is not significant for trend detection on the time series. Thus, the authors can add one the non-parametric test such as Man Kendell or Pettit tests. In addition, Innovative trend methodology can be also applied.
2- REMSE only is not sufficient to make a good decision regarding the model performance. Thus, at least, NSE, MSE, and R2 are suggested for assessing the model performance
3- Figure 4e must be presented in a separate figure including observed SM compared with SM simulated CLM5.0 and another one observed SM compared with SM simulated ESA CCI
4- A new table must be added including the suggested performance criteria for simulated and observed SM values
5- The paper needs a table including a literature review about the performance of the proposed models for SM simulation, and the results obtained from this study.
6- What is the novelty of this research compared to other studies?
7- Discussion must be added as a separate section
8- In conclusion, what are the limitations of this study and future recommendations?
Reviewer.
Comments for author File: Comments.pdf
Moderate editing of the english language is required
Author Response
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Reviewer 5 Report
I read the manuscript carefully, and I think it needs some improvements before it can be published.
1.I suggest that authors refine the expression abstract and highlight the innovation and necessity of research.
2.Proofreading of the manuscript by an expert of English language is required.
3.The discussion section needs to be improved, including "comparison with other experts", "limitations of this study", etc. In addition, the corresponding references should be added.
Proofreading of the manuscript by an expert of English language is required.
Author Response
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Reviewer 6 Report
The manuscript titled “Impact of climate change on the spatio-temporal variation of groundwater storage in the Guangdong-Hong Kong-Macao Greater Bay Area” has been reviewed. The objective of the study was to determine groundwater storage changes in the Greater Bay Area by combining data from the gravity recovery and climate experiment (GRACE) satellite and land surface models. The paper has scholarly significance and my recommendation is that it should be considered for publication. However, the following comments must be addressed by the authors:
1. The description given to groundwater is not correct (refer to line 53). Groundwater is water is found in rock formations.
2. The time duration is inconsistent. In line 95, the authors refer to 2002-2018, whereas in line 110, reference is made to 1979-2018.
3. The time frame for the datasets appears to be different. How did the authors synthesize all the datasets in a common duration?
4. Refer to all equations in the text before they are presented.
5. There has to be a statement or two on why the RMSE statistical indicator was used for the research.
6. For a study of this nature, it is important to present a flowchart for all the methods that were employed.
7. The discussion under section 3.1 (Spatio-temporal Distribution of GWSA) could be improved. What is the significance of the observed decreasing/increasing trends?
8. The information in Figure 6 cannot be considered a spatial distribution, but rather trend.
9. Figure 7 talks about spatial distribution. However, the caption is not a true reflection. For example, Figure 7a and b indicate precipitation values at two different times. Therefore, the name “trend” cannot describe Figure 7.
10. The are some areas where some of the text are together and needs to be corrected.
11. There is a citation in the conclusion. This is not acceptable and should be reviewed.
The article has scholarly importance and is therefore recommended for publication subject to the minor revision.
Author Response
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Round 2
Reviewer 1 Report
Author Response
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Reviewer 3 Report
1. It’s recommended to place Figure 3 into the Results section instead of the Materials and Methods section.
2. I suggest to entitle Section 3 as Results and Section 4 as Discussions.
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Reviewer 4 Report
I am writing in regard to manuscript ID sustainability- 2399344 entitled “Impact of climate change on the spatio-temporal variation of groundwater storage in the Guangdong-Hong Kong-Macao Greater Bay Area”, which was submitted to the Sustainability MDPI. I think the authors for the improvements that have been done during the first round of revision.
After careful review, one minor revision that I would recommend the author consider:
- Please add more details to the Table 1 (Why there is a statistical results for one location)
Minor editing of English language required
Author Response
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