Sentinel-2 MSI Observations of Water Clarity in Inland Waters across Hainan Island and Implications for SDG 6.3.2 Evaluation

Round 1

Reviewer 1 Report

The study “Sentinel-2 MSI observations of water clarity in inland waters across Hainan Island and implications for SDG6.3.2 evaluation” presents an interesting and important study for the scientific community. The results of the study are promising for the scientific community, making it possible to establish strategies for the conservation of water bodies in the region, helping in local public policies. However, before recommending the present study for publication, some points need correction. Therefore, I am considering this manuscript for minor revisions, highlighting as major observations:

 

• In my reading, I detected several errors in the writing of the work, therefore, I suggest to the authors a deep revision in the writing of the manuscript by a fluent in the language.

• Is just the results addressed in terms of water clarity enough to associate the different agents that can influence the dynamics of the waters? I see it as a superficial analysis to characterize the different effects and attenuating agents on the island of Hainan.

As a suggestion to the authors, explore the calculation of the NDCI for chlorophyll-a (https://doi.org/10.1016/j.rse.2011.10.016), as water clarity alone does not significantly explain the aspects that influence the dynamics of these waters.

• Why did the authors not bring a water turbidity index via remote sensing techniques? Works such as (https://doi.org/10.1016/j.rsase.2020.100382) and (https://doi.org/10.1016/j.jsames.2022.103965), present Turbidity and highlight the importance of exploring this variable in the characterization of water contaminants.

• In conclusion to my main observations, I find it interesting for the authors to present at least one of the aforementioned indexes in their study, as in my opinion, it will further increase the quality of the present study.

 

 

As minor observations, I bring:

1 – According to the rules of Remote Sensing, only 300 words are allowed in the abstract, the authors present 344 words. The abstract must be synthesized!!!

 

2 – I suggest authors replace the last keyword with a shorter one.

 

3 – Before subtopic 2.1., it would be interesting for the authors to bring a subtopic referring to “Characterization of the study area”, bringing information such as the number of inhabitants, Köppen-Geiger climate classification (https://doi.org/10.1038/sdata. 2018.214), annual precipitation based on climatological normals of 30 years of information, the average temperature in the region, topographic elevation (As a suggestion, explore the possibility of inserting it in Figure 1 itself via data from NASA's SRTM) and others.

 

4 – In Figure 1, the authors need to remove the latitude and longitude from the right and bottom of the two figures.

 

5 – In table 4 remove the indentation to “443 nm”.

 

6 – In Figure 6 (a) align the information of N, R2, MRE, and RMSE with those in Figure 6 (b), 6 (a) has a large indentation.

 

7 – Do the authors consider the values of the coefficient of determination lower than 0.60 significant?

 

8 – In Figure 9, I suggest the authors increase the distance of the letter “km” from the scale of the figure, as I am finding them very close.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors!

In terms of presentation quality, this is a very good manuscript!

However, I do not understand the relevance of the article... assessment of transparency as one of the indicators of water quality.

Yes, of course, water transparency is an important indicator, but it does not determine the quality of water ...

The conclusions of the authors regarding precipitation and changes in transparency are quite understandable, studies of the effect of vegetation cover on water transparency are completely unfounded...

I will give you an example. To take into account the effect of precipitation on transparency, it is necessary to take into account their amount, intensity, and depth of penetration into water bodies. In addition, it is necessary to take into account bottom sediments, how quickly do they erode and affect transparency? And this is only one side of the issue.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Sentinel-2 MSI observations of water clarity in inland waters across Hainan Island and implications for SDG6.3.2 evaluation:

·        In the last paragraph of the Introduction, the authors should mention the weak point of former works (identification of the gaps) and describe the novelties of the current investigation to justify that the paper deserves to be published in this journal.

·        Discuss more the spatiotemporal dynamics of lake clarity in the Hainan Province during 2017–2021.

·        Discuss the most important reasons for the variations of the Proportion of the average annual transparent water bodies in the dry season and rainy season of inland water bodies in the Hainan Island from 2017–2021.

·        “After 2018, there was a significant increase in the proportion of water bodies with good water quality in the Hainan Island.”. Why?

·        “Spatially, it was found the water clarity of inland waters in central regions was generally higher than that in the coastal regions.”. Why? Explain.

·        Focus on the advantages/disadvantages of the proposed method concerning the obtained results.

·        What are the strategies/recommendations to reduce uncertainties in this study?

·        How can expand the results to other regions with similar/different climates?

 

·        The quality of the language needs to be improved for grammatical style and word use.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thank you for your answers, however, I cannot agree with them, because a deeper analysis of all acting factors should be given to assess the quality of water. I hope that this recommendation will be taken into account in future studies.

Reviewer 3 Report

I appreciate the authors addressing the comments. The manuscript can be accepted in its current form. Congrats!