Spatiotemporal Variability of the Lake Tana Water Quality Derived from the MODIS-Based Forel–Ule Index: The Roles of Hydrometeorological and Surface Processes
Round 1
Reviewer 1 Report
In work entitled " Spatio-temporal variability of Lake Tana Water quality derived from MODIS-based Forel-Ule Index: The role of hydrometeorological and surface processes” by Abegaz et al., ; the Authors demonstrated the role of hydrometeorological and surface processes on Spatio-temporal variability of Lake Tana. However, the author needs some improvements in the text for better readability and some modification in the figures.
Keywords:
Comment 1: It is better to avoid the abbreviation, for example, FUI
Abstract:
Overall, the contents of the abstract is enough; however, authors should improve the readability of the Abstract by better arranging the text. For example….
Comment 2: Please rephrase “Lake Tana, the biggest inland water body in Ethiopia, has witnessed significant changes in and around the Lake due to ongoing urbanization and socioeconomic activities in recent times” as
“Lake Tana, the biggest inland water body in Ethiopia, has witnessed significant changes due to on-going urbanization and socioeconomic activities in recent times”
Comment 3: It is better to delete “The lake is a source of income for many livelihoods in the region. ”
Comment 4: SPEI is not defined.
Introduction:
Comment 5: Overall, the Introduction is well-written and organized, it needs to add some recent studies and discuss the limitations and needs of the present study.
Comment 5: Figures' colorbar scales are not good in all the shaded plots.
For example, in figure 4, only 6 colors represent for 11 values. Thus, it is not possible to identify the values of corresponding colors. Which color represents -.4 and -.6. Please update the figures.
Author Response
Manuscript ID: atmosphere-2096543
Response to Reviewers
Thank you for giving us the opportunity to submit a revised draft of the manuscript “Spatio-temporal variability of Lake Tana Water quality derived from MODIS-based Forel-Ule Index: The role of hydro-meteorological and surface processes ” for publication in the Journal of Atmosphere. We appreciate the time and effort that you and the reviewers dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. We have incorporated all of the suggestions made by the reviewers. Those changes are included within the manuscript. Please see below, in blue, for a point-by-point response to the reviewers’ comments and concerns. All page numbers refer to the revised manuscript file with tracked changes.
Reviewers' Comments to the Authors:
Reviewer 1
In work entitled " Spatio-temporal variability of Lake Tana Water quality derived from MODIS based Forel-Ule Index: The role of hydro-meteorological and surface processes” by Abegaz et al., ; the Authors demonstrated the role of hydro-meteorological and surface processes on spatio-temporal variability of Lake Tana. However, the author needs some improvements in the text for better readability and some modification in the figures.
Author response: We thank the reviewer for the suggestion. We have made a number of rewriting in different parts of the revised manuscript to improve readability and amended all the figures as suggested by the reviewer.
1. It is better to avoid the abbreviation, for example, FUI
Author response: Thank you for pointing this out. The reviewer is correct, and we have [changed “FUI” to “Forel-Ule Index” , “MODIS” to “ Moderate Resolution Imaging Spectroradiometer” and “LULC” to “ Land use and land cover” ]. The revised text is found in lines 44-45
2. Please rephrase “Lake Tana, the biggest inland water body in Ethiopia, has witnessed significant changes in and around the Lake due to ongoing urbanization and socioeconomic activities in recent times” as “Lake Tana, the biggest inland water body in Ethiopia, has witnessed significant changes due to on-going urbanization and socioeconomic activities in recent times”
Author response: Thank you for this suggestion. The revised text is now found in lines 12-13.
3. It is better to delete “The lake is a source of income for many livelihoods in the region”.
Author response: Thank you for this suggestion. We amend accordingly.
4. SPEI is not defined.
Author response: Thank you for pointing this out. The revised text is found in lines 31-32.
5. Overall, the Introduction is well-written and organized, it needs to add some recent studies and discuss the limitations and needs of the present study.
Author response: We agree with the reviewer’s assessment. Accordingly, we have added some recent studies and their limitations in the introduction. The text is found in the revised manuscript on page 3 line numbers 108-111 and 118-120.
6. Figures' color bar scales are not good in all the shaded plots. For example, in figure 4, only 6 colors represent for 11 values. Thus, it is not possible to identify the values of corresponding colors. Which color represents -.4 and -.6. Please update the figures.
Author response: Thank you for this suggestion. Accordingly, throughout the manuscript, we have revised all figures and their color bars.
Reviewer 2 Report
The manuscript entitled Spatio-temporal variability of Lake Tana Water quality derived
from MODIS-based Forel-Ule Index: The role of hydrometeorological and surface processes after Major Revision.
In my opinion, the subject of this work is relevant for the Journal Atmosphere MDPI after major revisions and approved corrections.
The topic of the paper, is very interesting and important, especially in the context of the Remote sensing in analysis and hydrometeorological surface processes
The Journal Atmosphere MDPI wants interesting and quality papers.
First, before all the paper has the next sections and sub-sections (i.e. Abstract, Introduction, Study area and data sets, Description of study area, Datasets, MODIS water surface reflectance dataset, Diversity II dataset, Reanalysis and observational datasets, land use and land cover change datasets, Methods, Correction for spectral reflectance of day light and sky light in MOD09A1 reflectance, FUI formulation, FUI-based trophic state assessment of lake Tana water, Categorical statistics, Composite analysis for establishing qualitative causal linkage between FUI and environmenta, Factors, Results and discussion, Performance of FUI as a trophic state indicator based on categorical statistical metrics and pearson correlation, The spatio-temporal variablity of FUI of the Lake Tana water, FUI composites over Lake Tana under different direction of changes of the deriving factors, FUI composites under different ranges of temperature and evaporation, FUI composites under different ranges of precipitation and surface runoff, FUI composites under different ranges of wind speed, FUI composites under different ranges of NDVI and EVI, FUI composites under different classes of drought conditions, Conclusions, etc.)
I strongly recommend to the authors add a section of abbreviation because of the large number of short words (scientific terms).
The section of Abstract
The section of abstract is not fully explaining the main results of this research. The authors must add the main results and one sentence to explain how this research get influence on of Lake Tana Water quality in connection with MODIS satellite recordings. Also, in this section the authors have large number of abbreviations and it is not usual in this stage of the paper.
The section of Introduction
The authors next time must obligatory add line numbering. The line numbers are good for reviewers to better marks all mistakes and comments within the text.
For this rank of Journal, the section of Introduction is overall short. The authors must add more references which reflect connection between satellite data and MODIS. MODIS or Moderate Resolution Imaging Spetroradiometer is good in showing land, water and atmosphere changes. There are many valuable papers which showed MODIS recordings and connection with spatial changes. I recommend two
- Valjarević, A., Popovici, C., Djekić, T., Morar, C., Filipović, D., Lukić, T., 2022.
Long-term monitoring of high optical imagery of the stratospheric clouds and their properties new approaches and conclusions. The Egyptian Journal of Remote Sensing Space Science, 25(4), 1037-1043. https://doi.org/10.1016/j.ejrs.2022.11.006.
- M. L. Carroll, C. M. DiMiceli, J. R. G. Townshend, R. A. Sohlberg, A. I. Elders, S. Devadiga, A. M. Sayer & R. C. Levy (2017) Development of an operational land water mask for MODIS Collection 6, and influence on downstream data products, International Journal of Digital Earth, 10:2, 207-218, DOI: 10.1080/17538947.2016.1232756.
Study area and data sets
In this section the authors must explain better investigated area and more data about Lake Tana. Also, the authors must add more about general climate properties and geographical position in comparison with other parts of the country.
Subsection datasets
The authors labeled that used MODIS water surface reflectance dataset in resolution of 500 m. Is it possible to find better resolution? Can the authors show link where they downloaded data?
Subsection Diversity II dataset
In this section the authors didn’t explain in good way and order how they created lake properties and borders?
Did the author used supervised or unsupervised classifications? Which software of GIS they are used?
Figure 1.
Please, change the color of water to be more realistic on right picture. The color is too greener.
With this trophic index equation your cited formula can be compared and commented.
ln 1 = 0
6 – 0 = 6
6 = 60
Therefore, the TSI of a 1 meter Secchi depth is 60. If the Secchi depth were 2 meters,
ln 2 / ln 2 = 1
6 – 1 = 5
10 x 5 = 50
The indices for the chlorophyll and total phosphorus are derived in a similar manner, but, instead of a Secchi depth value in the numerator, the empirical relationship between chlorophyll or total phosphorus and Secchi depth is given instead. For example, the chlorophyll TSI is:
The above forms of the TSI equations may illustrate how the indices were derived, but they can be simplified for everyday use. The simplified equations are below:
TSI(SD) = 60 – 14.41 ln(SD)
TSI(CHL) = 9.81 ln(CHL) + 30.6
TSI(TP) = 14.42 ln(TP) + 4.15
Section of Methods
The Equation 2.
This equation 2 describe formula of near-infrared bands from the visible
bands. Can the authors in this section included formula which explain correction of recordings when haze, cloudiness and fog get an influence of quality of recordings.
Below of this sentence For MODIS, the CIE tristimulus
values are obtained from, please put the numeration of Equation.
Below of this Equation I think that this equation is not necessary to be in the text.
The same for the Table 1,
The statistic in this section used in this research is not enough. So, I recommend to the authors to analyze better all results with some advanced statistical tool or software.
Below of the Figure 4, the authors labeled p<0.05. Can the authors better explain which statistical software they used to analyze statistical significant.
Can the authors in the section Results and Discussion better describe water properties variability in weekly, monthly and seasonal scale?
The section of Conclusion
In this section, the authors must answer on following questions?
Why this research is important?
Did the authors find a connection between MODIS data and Tana Water quality?
How is the forecast for this lake?
Please, add more results and main goals in the section of the Conclusion.
This paper has the potential to be published. The authors did a lot of things within this manuscript. The paper is very interesting and scientifically correct.
In the end, I recommend Major Revision.
Good luck to the authors
The Reviewer#2
Author Response
Manuscript ID: atmosphere-2096543
Response to Reviewers
Thank you for giving us the opportunity to submit a revised draft of the manuscript “Spatio-temporal variability of Lake Tana Water quality derived from MODIS-based Forel-Ule Index: The role of hydro-meteorological and surface processes ” for publication in the Journal of Atmosphere. We appreciate the time and effort that you and the reviewers dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. We have incorporated all of the suggestions made by the reviewers. Those changes are included within the manuscript. Please see below, in blue, for a point-by-point response to the reviewers’ comments and concerns. All page numbers refer to the revised manuscript file with tracked changes.
Reviewer 2
1. I strongly recommend to the authors add a section of abbreviation because of the large number of short words (scientific terms).
Author response: Thank you for your recommendation. We added the section of abbreviation in our revised paper on page 21-22.
2. The authors next time must obligatory add line numbering. The line numbers are good for reviewers to better marks all mistakes and comments within the text.
Author response: As suggested by the reviewer, we have added the line numbers to the manuscript.
3. The section of abstract is not fully explaining the main results of this research. The authors must add the main results and one sentence to explain how this research get influence on of Lake Tana Water quality in connection with MODIS satellite recordings. Also, in this section the authors have large number of abbreviations and it is not usual in this stage of the paper.
Author response: We agree with the reviewer’s assessment. Accordingly, we have revised and include the reviewer suggestion in the abstract. “These changes are indicated in the revised paper in line numbers 12-17 and 20-24 ”.
3. For this rank of Journal, the section of Introduction is overall short. The authors must add more references which reflect connection between satellite data and MODIS. MODIS or Moderate Resolution Imaging Spectroradiometer is good in showing land, water and atmosphere changes. There are many valuable papers which showed MODIS recordings and connection with spatial changes. I recommend two.
Author response: As suggested by the reviewer, we have added some recent studies including papers recommended by the reviewer on the introduction part of the paper. The text is found on page 3, line numbers 108-111 and 118-120.
4. In this section the authors must explain better investigated area and more data about Lake Tana. Also, the authors must add more about general climate properties and geographical position in comparison with other parts of the country.
Author response: We agree with the reviewer’s assessment, and we have included details of our study area. The text that we added is found on pages 3-4, line numbers 138-150 and 154-160.
5. The authors labeled that used MODIS water surface reflectance dataset in resolution of 500m. Is it possible to find better resolution? Can the authors show link where they downloaded data?
Author response: There is higher resolution than the MOD09A1 (500m resolution) surface reflectance which is an 8-day composite, well geo-referenced, integrated, and cloud stamped data set and has been extensively utilized for monitoring of the long term variability of water quality globally. Because of this reason we use 500m resolution data sets. Although there is 250 m resolution, it is restricted to band 1 and 2 and cannot be used for this kind of study. The link from where the data was downloaded is already listed in page-4 line number 166.
6. In this section the authors didn’t explain in good way and order how they created lake properties and borders? Did the author used supervised or unsupervised classifications? Which software of GIS they are used?
Response: The observations of the reviewer is ok but missed a piece of important information. The main aim of this study is to estimate lake water quality in terms of FUI and assess how hydro-meteorological and land use and land cover variables affect water quality. So, the description of how Diversity-II datasets are generated is already explained on their platforms (http://www.diversity2.info/products/) and publications therein, and it is not the focus of this work. The published water quality parameters such as CDOM TSM, chl_a, and turbidity provided by Diversity-II platform from the European Space Agency(ESA) are based on more advanced retrieval approach and can be used to assess the quality of more simplified index, FUI, derived from reflectance measurements by inspecting the correlation between water quality parameters and FUI. Moreover, the skill of FUI relative to TSI derived from Diversity-II data in capturing trophic state of the lake water is evaluated based on categorical statistical metrics. We have never used for either calculating FUI nor producing the figures. Codes written in Matlab are used in all our analysis except map in Fig.1. Moreover, we have not done any supervised or unsupervised classification. In this regard, we are a bit lost to understand what the last two statements of the reviewer are referring.
7. Please, change the color of water to be more realistic on right picture. The color is too greener.
Author response: Thank you for pointing this out. Based on the reviewer’s suggestion we have changed the color of the water in figure 1.
8. The indices for the chlorophyll and total phosphorus are derived in a similar manner, but, instead of a Secchi depth value in the numerator, the empirical relationship between chlorophyll or total phosphorus and Secchi depth is given instead. For example, the chlorophyll TSI is: The forms of the TSI equations may illustrate how the indices were derived, but they can be simplified for everyday use.
Author response: We thank the reviewer for insightful analysis. We used the simplified form of equation 1 as suggested by the reviewer.
9. This equation 2 describe formula of near-infrared bands from the visible bands. Can the authors in this section included formula which explain correction of recordings when haze, cloudiness and fog get an influence of quality of recordings.
Response: The reviewers' comment is good. But MOD09A1 (level-2) datasets are already undergone through atmospheric correction including correction of aerosol scattering, correction of air molecule scattering, and correction of cirrus. Besides, there is quality flag associated with each pixel reflectance measurements with respect presence of cloud, cloud shadow, aerosol and cirrus clouds near the scene of the pixel. We have used the highest quality that excludes cloud, cloud shadow, aerosol and cirrus clouds. The additional correction method that is used in this paper is to do further correction to remove water surface spectral reflectance as suggested by Shenglie et,al., 2016.
10. Below of this sentence For MODIS, the CIE tristimulus values are obtained from, please put the numeration of Equation.
Author response: Thank you for pointing this out. Based on the reviewer’s suggestion we have put the equation number of the formula on page-6.
11. Below of this Equation I think that this equation is not necessary to be in the text. The same for the Table 1,
Author response: Thank you for pointing this out. But the reason that we put the equation as well as the table in the text is to make our paper easily understood by the readers.
12. The statistic in this section used in this research is not enough. So, I recommend to the authors to analyze better all results with some advanced statistical tool or software.
Author response: Thanks for your comment. We used advanced statistical analysis in our study such as pearson correlation, categorical statistics and composite analysis.
13. Below of the Figure 4, the authors labeled p<0.05. Can the authors better explain which statistical software they used to analyze statistical significant.
Author response: Thanks for your comment. We have used Matlab software to analyze the statistical significant level of correlation in figure-4 and we have explained it in the caption of the figure.
14. Can the authors in the section Results and Discussion better describe water properties variability in weekly, monthly and seasonal scale?
Author response: Thank you for this suggestion. The aim of the work is not only assessing the variability of water quality, it also to demonstrate the impacts of hydro-meteorological and land use and land cover variables on the variability of water quality. We found that the impacts of hydro-meteorological and land use and land cover variables is clearly seen in monthly and seasonal scales. Moreover, due to data gaps arising from filtering out low quality data, higher temporal resolution than monthly is not feasible. So we are focused on the discussion of lake water quality in annual, inter annual and seasonal scales. Figures 5-8 and their discussion show the spatial as well as temporal variability of water quality in terms of FUI.
15. Please, add more results and main goals in the section of Conclusion.
Author response: We agree with the reviewer’s assessment. Accordingly, we have amended the conclusion.
Reviewer 3 Report
The paper examines the lake quality index and has used satellite data in this regard. The paper has a good innovation and is acceptable with the existing conditions.
Author Response
Manuscript ID: atmosphere-2096543
Response to Reviewers
Thank you for giving us the opportunity to submit a revised draft of the manuscript “Spatio-temporal variability of Lake Tana Water quality derived from MODIS-based Forel-Ule Index: The role of hydro-meteorological and surface processes ” for publication in the Journal of Atmosphere. We appreciate the time and effort that you and the reviewers dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. We have incorporated all of the suggestions made by the reviewers. Those changes are included within the manuscript. Please see below, in blue, for a point-by-point response to the reviewers’ comments and concerns. All page numbers refer to the revised manuscript file with tracked changes.
Reviewer 3
The paper examines the lake quality index and has used satellite data in this regard. The paper has a good innovation and is acceptable with the existing conditions.
Author response: Thanks a lot for your review.
Round 2
Reviewer 2 Report
The manuscript Spatio-temporal variability of Lake Tana Water quality derived from MODIS-based Forel-Ule Index: The role of hydrometeorological and surface processes can be accepted. The authors answered all of my comments and corrected all of the mistakes within the text.
In my opinion, this manuscript can be accepted in its present form.
Sincerely,
The Reviewer #3
Comments for author File: 
Comments.docx
