Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript, Water resources monitoring in remote region: Earth-observation-based study of endorheic lakes, apparently presents a novel methodology to identify changes in precipitation over time in three lakes based on the variation of water levels; however, there are many doubts regarding the accuracy of the information, mainly when only the correlation between the area that varies in the lake as a function of precipitation and the lack of data that is not contemplated for the entire measurement period is evaluated.

 Although the manuscript is interesting, it should take into account what happens at the bed of the lake since the area may or may not increase as a function of rainfall. The characteristics of the relief below the area that floods, as well as the relief on the slopes, should be considered.

Figure 3 shows the area of Lake Chungará compared to the total annual precipitation between 1987 and 2019; however, some doubts arise.

1. How is it that for 1987, the precipitation was approximately 310 mm, and the lake area was 22.9 km2. On the other hand, for 2007, 2008, and 2009, the precipitation is almost equal to approximately 300 mm, while the area is 21.6, 21.8, and 20.8 km2. What is the reason for this variation in the extension of the lake? Does the relief not influence this variation? If it does, where do the authors consider it?

2. Analyzing the relief from a digital elevation model is essential. The authors should clarify the variability in the behavior of lake extension in relation to rainfall. Although it is indicated that the lakes are in flat areas, this is not always true since the bed of the lakes varies according to the transport and deposition of sediments that occur on the hills surrounding the lakes. Also they indicate that some lakes has depths ranging from 26 to 40 meters.

3. I consider that the low correlations, in addition to the data used, also have to do with the relief that, from my point of view, is not being considered.

I respectfully suggest to the authors that the methodology be revised and that the manuscript be restructured so that it is feasible for publication.

Author Response

We hereby present the review of the article "Water Resources Monitoring in Remote Regions: An Earth-Observation-Based Study of Endorheic Lakes." We appreciate the detailed analysis provided by the reviewers and believe that the suggested changes have enriched the work, making the text clearer to the readers.

First, we are very pleased with the reviewers' comments. The manuscript has been revised and improved to address the reviewers' main comments, including revisions to the abstract, introduction, methodology, and the discussion surrounding lake morphology. The text has been revised and improved, with figure and table added to clarify the manuscript.

 

Comments and Suggestions for Authors

The manuscript, Water resources monitoring in remote region: Earth-observation-based study of endorheic lakes, apparently presents a novel methodology to identify changes in precipitation over time in three lakes based on the variation of water levels; however, there are many doubts regarding the accuracy of the information, mainly when only the correlation between the area that varies in the lake as a function of precipitation and the lack of data that is not contemplated for the entire measurement period is evaluated.

 Although the manuscript is interesting, it should take into account what happens at the bed of the lake since the area may or may not increase as a function of rainfall. The characteristics of the relief below the area that floods, as well as the relief on the slopes, should be considered.

Figure 3 shows the area of Lake Chungará compared to the total annual precipitation between 1987 and 2019; however, some doubts arise.

 

 

1. How is it that for 1987, the precipitation was approximately 310 mm, and the lake area was 22.9 km2. On the other hand, for 2007, 2008, and 2009, the precipitation is almost equal to approximately 300 mm, while the area is 21.6, 21.8, and 20.8 km2. What is the reason for this variation in the extension of the lake? Does the relief not influence this variation? If it does, where do the authors consider it?

We believe that the data show trends rather than absolute values. The authors acknowledge potential issues arising from the use of different satellite series and the existence of variations due to the dates of image acquisition before and after the rainy seasons. However, the 5% variation in the total lake area can be considered an outlier. The study discusses the limitations of the presented methodology (lines 358-371); nevertheless, it is an innovative methodology for monitoring water resources in areas with logistical constraints (i.e., remote and difficult to access).

The observed variations in lake extent despite similar precipitation levels can also be attributed to these factors. Although relief does influence lake extent, as discussed, the primary focus of our methodology is on capturing general trends rather than precise measurements. This approach is particularly suitable for remote areas where on-the-ground measurements are not feasible. Therefore, while the relief does play a role, our methodology primarily aims to provide a practical and innovative means of monitoring hydrological changes in challenging environments.

2. Analyzing the relief from a digital elevation model is essential. The authors should clarify the variability in the behavior of lake extension in relation to rainfall. Although it is indicated that the lakes are in flat areas, this is not always true since the bed of the lakes varies according to the transport and deposition of sediments that occur on the hills surrounding the lakes. Also they indicate that some lakes has depths ranging from 26 to 40 meters.

We have added a detailed description related to the basin metrics derived from topographic variations using SRTM data in the “2. Materials and methods” section. We clarify that the objective of the study is not to analyze the water volume but the water surface area. Temporal analyses of the relief and land use around the lakes did not indicate significant or abrupt changes, such as tectonic activities or landslides, in the area. The watersheds are relatively stable.

We understand the reviewer's concern regarding depth calculation; however, we clarify that due to the remote nature of the studied areas, it is not possible to perform the depth calculation necessary for volumetric analysis of the water body. Our focus remains on the association with the water surface area, using the available data to provide an accurate and relevant analysis. Additionally, we emphasize that the variations in lake extension in response to rainfall were evaluated based on water surface area data, which adequately reflect the dynamics of the flooded areas, especially in regions where the topography is relatively flat but with small local variations due to sedimentation.

This approach allows us to better understand the relationship between precipitation and the extent of water surfaces, respecting the limitations imposed by the lack of precise volumetric data. Finally, we reinforce that the analysis conducted significantly contributes to the understanding of the hydrological dynamics of the studied areas, within the limitations and scope outlined for this study.

3. I consider that the low correlations, in addition to the data used, also have to do with the relief that, from my point of view, is not being considered.

We agree that the low correlation may be related to the geomorphological characteristics of the reservoirs, as described in lines 372-375. Although the relief plays a role, our methodology primarily aims to provide a practical and innovative means of monitoring hydrological changes in challenging environments. Therefore, the influence of the relief was considered within the described limitations, and our results reflect these conditions.

 

I respectfully suggest to the authors that the methodology be revised and that the manuscript be restructured so that it is feasible for publication.

We have updated, improved and revised the text, particularly the methodology section, by adding more details and including a methodology flowchart.

Reviewer 2 Report

Comments and Suggestions for Authors

Comments and Suggestions for Authors

Review Report on remotesensing-3027393

General comments:

In this paper, the authors aim at quantify the extension of endorheic lakes and correlate this information with precipitation data by exploiting a GEE-based tool based on Landsat-OLI8, Landsat-ETM+, Landsat-TM5 and MODIS time series (from 1975 to 2019).

Generally speaking, the manuscript shows a weak innovative aspect with a writing style and paper organization that makes the work more similar to a report than a scientific paper. Furthermore, the work relies on simple statistically-based analysis that contribute to achieve obvious results and/or of questionable scientific interest. In some cases, the achieved findings are not properly satisfactory in terms of statistical significance (see low coefficient of determination) and this aspect contribute to expose the work to heavy limitations and poor exportability to other case studies. The methodological approach (i.e., GEE-based tool), that should be the main innovative aspect of the work, appears to be based simply on a RGB-based visual inspection and is not in-depth described. Furthermore, the relevant criticisms about satellite data processing concern the reflectance data exploited for such an analysis. Within this paper, the authors did not refer to any atmospheric correction method and the possibility to analyze not-atmospherically corrected data is not acceptable. The atmospheric correction for inland waters (lakes) plays a key role in retrieving accurate Rrs(λ) (remote sensing reflectance) estimates and consequently in reliable/incorrect detecting of land/water pixel useful to delineate lakes’ extension. In light of these considerations, I think the paper requires a heavy re-organization hampering publication as it is now.

 

Author Response

Reviewer 2

We hereby present the review of the article "Water Resources Monitoring in Remote Regions: An Earth-Observation-Based Study of Endorheic Lakes." We appreciate the detailed analysis provided by the reviewers and believe that the suggested changes have enriched the work, making the text clearer to the readers.

First, we are very pleased with the reviewers' comments. The manuscript has been revised and improved to address the reviewers' main comments, including revisions to the abstract, introduction, methodology, and the discussion surrounding lake morphology. The text has been revised and improved, with figure and table added to clarify the manuscript.

 

Comments and Suggestions for Authors

Review Report on remotesensing-3027393

General comments:

In this paper, the authors aim at quantify the extension of endorheic lakes and correlate this information with precipitation data by exploiting a GEE-based tool based on Landsat-OLI8, Landsat-ETM+, Landsat-TM5 and MODIS time series (from 1975 to 2019).

Generally speaking, the manuscript shows a weak innovative aspect with a writing style and paper organization that makes the work more similar to a report than a scientific paper. Furthermore, the work relies on simple statistically-based analysis that contribute to achieve obvious results and/or of questionable scientific interest. In some cases, the achieved findings are not properly satisfactory in terms of statistical significance (see low coefficient of determination) and this aspect contribute to expose the work to heavy limitations and poor exportability to other case studies. The methodological approach (i.e., GEE-based tool), that should be the main innovative aspect of the work, appears to be based simply on a RGB-based visual inspection and is not in-depth described. Furthermore, the relevant criticisms about satellite data processing concern the reflectance data exploited for such an analysis. Within this paper, the authors did not refer to any atmospheric correction method and the possibility to analyze not-atmospherically corrected data is not acceptable. The atmospheric correction for inland waters (lakes) plays a key role in retrieving accurate Rrs(λ) (remote sensing reflectance) estimates and consequently in reliable/incorrect detecting of land/water pixel useful to delineate lakes’ extension. In light of these considerations, I think the paper requires a heavy re-organization hampering publication as it is now.

 

The work presents an innovative methodology in an attempt to assess the debate surrounding precipitation pattern changes in the Chilean highlands over recent decades, utilizing fluctuations in water levels of endorheic lakes as natural precipitation indicators. The methodology used for delineating water bodies is described in other scientific works and has been validated in publications since 2014. Additionally, we have made the script available on GitHub (lines 431 to 433) so that the methodology and processing can be replicated in any area.

We clarify that the images used are surface reflectance data provided by the USGS for data analysis. This procedure is detailed in the methodology section, as described in line 172, and has been replicated in other parts of the article to make the data source explicit.

We believe that utilizing a tool based on the Google Earth Engine (GEE) to monitor endorheic lakes in a remote and challenging region is a valuable approach. Our methodology, though simple, offers a practical and efficient means of analyzing hydrological changes, especially in hard-to-reach areas. Furthermore, the focus on using time series data from different satellites (Landsat-OLI8, Landsat-ETM+, Landsat-TM5) allows for a comprehensive analysis over an extensive period (from 1984 to 2024).

Regarding to Atmospheric correction in Google Earth Engine (GEE) is a complex process with various limitations. In this context, we use surface reflectance images, which are adjusted to remove atmospheric effects and provide a more accurate representation of the Earth's surface. This surface reflectance is made available by the agencies that supply the images, such as the United States Geological Survey (USGS).

Reviewer 3 Report

Comments and Suggestions for Authors

The article is titled 'Water resources monitoring in remote region: Earth-observation-based study of endorheic lakes'. The aim of this study is to assess climate changes (mainly precipitation) over recent decades, taking advantage of water level fluctuations in endorheic lakes. The authors used remote sensing data to construct a time series showing changes in the extent of three lakes  in the Chilean Altiplano  (Chungará, Miscanti, and Miniques).

My comments are as follows:

 - The abstract should be corrected, the purpose of the research, methods and results should be written

- I propose to combine subsections 2.1 and 2.2. name the research area. The morphometric data of the lakes should be presented in a table, and the next subsection 2.2 should name the data and research methods

- the methodological part should be presented in the form of a diagram

- In Fig. 1, mark the names of meteorological stations

- Analyzing only the lake surface and rainfall can only explain climate change issues to a limited extent. The authors should focus on land use in the lake's catchment area, including groundwater intakes that may affect the amount of water supply to the lake. A greater added value of this research would be if changes in the bathymetric plans of the lakes were presented. Changes in the water surface do not reflect climate change, especially since the analyzed period covers only 30 years and concerns total rainfall, without division into its type: snow or rain. Air temperature was also not taken into account in this study. Please note that lakes are naturally susceptible to disappearance.

- Please indicate what is new in this study, what research gaps this study fills and how effective the proposed methodology is

 

 

 

 

 

Author Response

We hereby present the review of the article "Water Resources Monitoring in Remote Regions: An Earth-Observation-Based Study of Endorheic Lakes." We appreciate the detailed analysis provided by the reviewers and believe that the suggested changes have enriched the work, making the text clearer to the readers.

First, we are very pleased with the reviewers' comments. The manuscript has been revised and improved to address the reviewers' main comments, including revisions to the abstract, introduction, methodology, and the discussion surrounding lake morphology. The text has been revised and improved, with figure and table added to clarify the manuscript.

Comments and Suggestions for Authors

The article is titled 'Water resources monitoring in remote region: Earth-observation-based study of endorheic lakes'. The aim of this study is to assess climate changes (mainly precipitation) over recent decades, taking advantage of water level fluctuations in endorheic lakes. The authors used remote sensing data to construct a time series showing changes in the extent of three lakes in the Chilean Altiplano (Chungará, Miscanti, and Miniques).

My comments are as follows:

 - The abstract should be corrected, the purpose of the research, methods and results should be written

The abstract has been improved following orientations.

 

- I propose to combine subsections 2.1 and 2.2. name the research area. The morphometric data of the lakes should be presented in a table, and the next subsection 2.2 should name the data and research methods

The metrics of the basins were included in the article as Table 1. The divisions were renamed according to the reviewer's guidance.

 

- the methodological part should be presented in the form of a diagram

The methodological flowchart was included as figure 2 in the article.

 

- In Fig. 1, mark the names of meteorological stations

The names of the stations were included in figure 1.

 

- Analyzing only the lake surface and rainfall can only explain climate change issues to a limited extent. The authors should focus on land use in the lake's catchment area, including groundwater intakes that may affect the amount of water supply to the lake. A greater added value of this research would be if changes in the bathymetric plans of the lakes were presented. Changes in the water surface do not reflect climate change, especially since the analyzed period covers only 30 years and concerns total rainfall, without division into its type: snow or rain. Air temperature was also not taken into account in this study. Please note that lakes are naturally susceptible to disappearance.

 

The paper presents an innovative methodology in an attempt to assess the debate surrounding precipitation pattern changes in the Chilean highlands over recent decades, utilizing fluctuations in water levels of endorheic lakes as natural precipitation indicators. The methodology used for delineating water bodies. However, the work assumes that there is a limitation to the methodology presented (lines 358-371); ideally, we would work with bathymetric data for volume calculations, however, as they are lakes in remote, practically inaccessible regions, there is no possibility of obtaining external data such as bathymetry, weather stations, and precipitation with division (snow or rain); the only source of temporal data are images from the Landsat family obtained in the last 40 years.

The Miniques and Miscanti Lakes basin is 40% located within the Los Flamencos National Park, a protected area with strict environmental regulations. We analyzed high-resolution images from December 2021, which demonstrate that there is no anthropogenic pressure or any type of land use and land cover change in this region.

 

- Please indicate what is new in this study, what research gaps this study fills and how effective the proposed methodology is

The paper presents an innovative methodology based on the Google Earth Engine (GEE) in an attempt to assess precipitation pattern changes in remote area where standard monitoring is challenging. The script is available on GitHub (lines 431 to 433, in the data availability statement section_ script for area calculation of water reservoirs in the Google Earth Engine platform: git clone: https://earthengine.googlesource.com/users/valadaolarissa/tocantinsReservoirsAreas (accessed on).) and the methodological flowchart allowed applying the tool in others area. The proposed tool with detailed methodology, GEE script and processing can be replicated in any area.

 

Reviewer 4 Report

Comments and Suggestions for Authors

Interest in this paper could be increased by stating how the reductions in lake area/volume could adversely affect human use and the ecology of the lakes.

Author Response

We hereby present the review of the article "Water Resources Monitoring in Remote Regions: An Earth-Observation-Based Study of Endorheic Lakes." We appreciate the detailed analysis provided by the reviewers and believe that the suggested changes have enriched the work, making the text clearer to the readers.

First, we are very pleased with the reviewers' comments. The manuscript has been revised and improved to address the reviewers' main comments, including revisions to the abstract, introduction, methodology, and the discussion surrounding lake morphology. The text has been revised and improved, with figure and table added to clarify the manuscript.

 

Interest in this paper could be increased by stating how the reductions in lake area/volume could adversely affect human use and the ecology of the lakes.

We agree that this will enhance the study and may be considered in future work conducted in the Altiplano area. Due to the difficult access to the studied areas, it is currently not possible to assess the adverse effects on human use and the ecology of the lakes.

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Review Report on remotesensing-3027393. Second review

 

Generally the revised manuscript shows appreciable improvements in terms of writing style and paper organization. In particular the the provided flow-chart about the GEE-based tool contributed to making the analysis methodology more understandable. However, I think the main issue of such a paper has not yet been properly resolved, as the authors did not provide a a comprehensive response about the atmospheric correction method adopted. The authors just argue that they use “surface reflectance images, which are adjusted to remove atmospheric effects and provide a more accurate representation of the Earth's surface”. To this aim:

- What does it mean “adjusted to remove atmospheric effects”? Rayleigh and aerosol corrections?

In my opinion, the adopted surface reflectances provided by USGS can be properly used for land applications but tehy need to be atmospherically corrected by methods designed to work in optically complex inland waters. At least the authors should highlight such a main limitation or criticism in the Discussion/Conclusion section.

Author Response

We hereby present the review of the article "Water Resources Monitoring in Remote Regions: An Earth-Observation-Based Study of Endorheic Lakes." We appreciate the detailed analysis provided by the reviewers and believe that the suggested changes have enriched the work, making the text clearer to the readers.

First, we are very pleased with the reviewers' comments. The manuscript has been revised and improved to address the reviewers' main comment.

However, I think the main issue of such a paper has not yet been properly resolved, as the authors did not provide a a comprehensive response about the atmospheric correction method adopted.

 

Surface reflectance datasets for Landsat 5 and 7 were generated by the Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) algorithm (1), and the Landsat 8 surface reflectance products were generated by the Landsat Surface Reflectance Code (LaSRC) algorithm (2). LaSRC uses the coastal aerosol band to perform aerosol inversion tests, employs auxiliary climatic data from MODIS, and uses a unique radiative transfer model. These atmospheric corrections have limitations for obtaining data related to water quality for optically active parameters such as total suspended matter, chlorophyll, turbidity, among others (3, 4, 5). However, the analysis for detecting flooded areas can be performed with reflectance data or even TOA data as demonstrated in studies 6, 7, and 8. Considering the objective of the analyses, we believe that the methodology, products, and types of corrections applied are appropriate and in accordance with recent international literature.

We correct and improve the manuscript to let clearer this issue, following:

Where it was “The areas were approximated using reflectance surface data from Landsat 5/TM, Landsat 7 ETM+, and Landsat 8/OLI satellites spanning from 1986 to 2019. In cases where Landsat data were unavailable for 2012 and 2013, MODIS (MOD09A1) data were utilized, despite the difference in resolution. Within the GEE platform, users can develop processing routines using JavaScript and access a variety of satellite images and sensors, facilitating a semi-automatic and rapid processing technique that is advantageous for time series studies.”

It as been substituted by : “We assumed that the volume of each lake correlates directly with its water surface extension. The areas were calculated using surface reflectance datasets from Landsat 5 and 7, generated by the Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) algorithm (Claverie et al., 2015), while the Landsat 8 surface reflectance products were generated by the Landsat Surface Reflectance Code (LaSRC) algorithm (Vermote et al., 2016). Despite limitations in water quality assessment, these data are routinely used for surface water mapping (Cao et al., 2022; Pickens et al., 2020; Pekel et al., 2016). In cases where Landsat data were unavailable for 2012 and 2013, MODIS (MOD09A1) data were utilized, despite the difference in resolution. Within the GEE platform, users can develop processing routines using JavaScript and access a variety of satellite images and sensors, facilitating a semi-automatic and rapid processing technique that is advantageous for time series studies.”

1. Claverie, M., Ju, J., Masek, J. G., Dungan, J. L., Vermote, E. F., Roger, J. C., ... & Skakun, S. (2015). The Harmonized Landsat and Sentinel-2 surface reflectance data set. Remote Sensing of Environment, 162, 331-340. https://doi.org/10.1016/j.rse.2015.02.008
2. Vermote, E., Justice, C., Claverie, M., & Franch, B. (2016). Preliminary analysis of the performance of the Landsat 8/OLI land surface reflectance product. Remote Sensing of Environment, 185, 46-56. https://doi.org/10.1016/j.rse.2016.04.008
3. Bernardo, N., Watanabe, F., Rodrigues, T., & Alcântara, E. (2017). Atmospheric correction issues for retrieving total suspended matter concentrations in inland waters using OLI/Landsat-8 image. Advances in Space Research, 59(9), 2335-2348. https://doi.org/10.1016/j.asr.2017.03.009
4. WANG, D., MA, R., XUE, K., LOISELLE, S. (2019). The Assessment of Landsat-8 OLI Atmospheric Correction Algorithms for Inland Waters. Remote Sensing, 11(2), 169. https://doi.org/10.3390/rs11020169
5. Cao, Y., Xue, Y., & Liu, Y. (2022). Monitoring surface water dynamics in the Yellow River Basin using Landsat time-series data and Google Earth Engine. Remote Sensing, 14(6), 1432. https://doi.org/10.3390/rs14061432
6. Segedi, G. C., Cicerelli, R. E., Almeida, T., Roig, H. L., Olivetti, D., Bernardi, J. V. E., & Castreghini, A. (2023). Analysis of the effects of atmospheric correction on orbital images for studies in interior water bodies. Revista Brasileira de Geografia Física (RAEGA), 16(7), 3465-3481. https://doi.org/10.5380/raega.v58i0.91408
7. Pickens, A. H., Hansen, M. C., Hancher, M., Stehman, S. V., Tyukavina, A., Potapov, P., Marroquin, B., & Sherani, Z. (2020). Mapping and sampling to characterize global inland water dynamics from 1999 to 2018 with full Landsat time-series. Remote Sensing of Environment, 243, 111792. https://doi.org/10.1016/j.rse.202 .111792
8. Pekel, J. F., Cottam, A., Gorelick, N., & Belward, A. S. (2016). High-resolution mapping of global surface water and its long-term changes. Nature, 540(7633), 418-422. https://doi.org/10.1038/nature20584

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have significantly improved the article. The proposed research method is not innovative and the results obtained do not bring anything new. In my opinion, the article has low scientific value. I leave the decision to the editor.

Author Response

We hereby present the review of the article "Water Resources Monitoring in Remote Regions: An Earth-Observation-Based Study of Endorheic Lakes." We appreciate the detailed analysis provided by the reviewers and believe that the suggested changes have enriched the work, making the text clearer to the readers.

First, we are very pleased with the reviewers' comments. The manuscript has been revised and improved.

We consider that the proposed approach also holds promise as a significant contribution to natural climate observatories in underserved and inadequately equipped areas like the Chilean Altiplano. It introduces an innovative method for proactively predicting water shortages and managing water resources. Additionally, it suggests strategies for safeguarding these invaluable lakes.

Ultimately, the dataset at our disposal empowers us to discuss recent climate fluctuations in this arid region for the first time. It substantially enhances our comprehension of the dynamics these lakes experience under anthropogenic pressures.

best regards