Snowfall Variation in Eastern Mediterranean Catchments

Round 1

Reviewer 1 Report

Voudouri et al., presented an interesting manuscript about the estimation of the snow in Greek and Italian regions. The presented topic is very relevant with many applications as environmental protection, hydrological and especially in hydrogeology because snow melting may be a relevant part of the recharge. The proposed results and elaborations are worth for publication even if major revisions are still necessary before the final acceptance. In addition, I detected some typos and repetitions. I suggest a revision of the text by an English mother tongue colleague

I report below my detailed comments/suggestions which may help the improvement of the manuscript:

Title: I have two main concerns about the title: the main result of the manuscript is the estimation of the snow parameters rather than the variability (not clear if spatial variability, seasonal oyearly); I suggest highlighting your main achieved results. The second concern is related to “selected”: this information suggest that the authors selected the areas according to some specific characteristics (based on geology, hydrogeology, climate…) but I can’t recognize this in the manuscript. I suggest to remove “selected”

Introduction:

In my opinion, the Introduction may be summarized removing the description of methods not used in the final elaboration and giving just a brief overview of the importance of snow data and their application.

Please check in the second page the paragraph since the ref. n°5. In this paragraph there are may sentences that could be removed because too vague and not related to your elaboration. Check also the two sentences starting with “for istance”

“Within this study….Mediterranean” mode this sentence in the last part of the introduction

“addition, the average snow coverage was found higher in January and the lowest in August” it seems to be an obvious information at our latitude. If not please detail better the relevance of this information

Synthetize the long list of possible applications and methods

Check the ref 22

“The overall goal is to better estimate and improve water resource management, based on the findings” I think your goal is to produce reliable data that may be later used to improve the water management

The paper is structured as follow: I don’t like the description of the structure of the article in the introduction because it should be coherent with the typical structure of an article (intro, matherials and methods, results discussion and conclusion). It’s a personal consideration but I suggest to the author to evaluate if this summary is necessary

Study area:

I suggest to the authors to check the toponyms reportend in the whole article and in the tables because sometimes they are not consistent.

The brief description of the study areas is nice but you should also include some information of altitude (min-max-average) because it is a relevant issue talking about snow

Study area 3: here you reported the climate data. Please include them also for the Greek areas.

Table 1 Datum information is missing. Include information about the study area because only Kozani is reported in the area 2. You reported only one station per area because it was the only one available or the most relevant

Figure 1 is not clear, I suggest to include the borders of the study areas, use a more visible pint for the 3 stations. I did not understand the use of the arrows and the presence of an additional point in Greece. Please check

Section 3: methodology. Why it is not under the 2 mateial and methods section?

4.1: “Snow depth derived from in situ measurements available for Mount Athos and Kozani station was employed”. Why the station Benevento was not taken in account?

Figure 3 and 4 are not very clear. The study areas are separated so I suggest to make 2 detail subfigures where the reads can see in more detail the results. Also the station name in red are not visible.

Looking at the results in Greece they seem to be consistent. In Italy the distribution of SWE (Fig3) seems relevant only on the seaside and not on the Apennine chain, please check

4.3 The linear fit slope values show similar temporal variability for SWE and SD for the two regions: maybe 3 regions?

The different trends described in this section should be highlighted also in the figure 6and 7

The data reported in the table 2 are mean values over the 3 study areas or are the values in correspondence of the 3 weather stations? If it is the average value maybe the authors may check if there is for example a reference value of altitude which may distinguish the subareas with a significant amount of snow rather than the sections were the snow amount is almost 0

Fig 8 the letters of the subfigures should stay close to the graphs to avoid any uncertainties.

Discussion:

I suggest to summarize the discussions focusing only on the discussion of your results. For example the sentences “the contribution of snowfall….water management strategies” (page 13) are not necessary and they don’t support your findings.

“In the last decade, the higher amounts of snowfall probably contributed to the replenishment of groundwater reserves”. I’m not sure about it just looking at the figure 9 without any other details on the monitored aquifer. Beside the snow depth significally increase since 2000, the groundwater levels arise only 14 years. The small peak in 2005 seems not relevant because since 2006 the groundwater decrease again with the same trend. Maybe information about yearly rainfall or the estimation of the groundwater withdrawals may support your discussion.

Why you did not provide any information also for the other two study areas?

Page 14 “ In recent years….RCP 8.5 scenario” not necessary discussion. Delete or summarize

“These are common sources of uncertainty when dealing with satellite data that might lead to untrustworthy values of the snow parameters” how much these uncertainities affect your results? Can you give an extimantion or just a brief comment?

“According to the public available….10% +-5.9%.” the snow cover extent is referred to glaciers or seasonal snow cover? I did not understand how the information reported in this section may support your results.

Conclusions

Point 4 should be detailed in the discussion section to be achieved as achived result

Author Response

Voudouri et al., presented an interesting manuscript about the estimation of the snow in Greek and Italian regions. The presented topic is very relevant with many applications as environmental protection, hydrological and especially in hydrogeology because snow melting may be a relevant part of the recharge. The proposed results and elaborations are worth for publication even if major revisions are still necessary before the final acceptance. In addition, I detected some typos and repetitions. I suggest a revision of the text by an English mother tongue colleague I report below my detailed comments/suggestions which may help the improvement of the manuscript:

We would like to thank the reviewer for his/her fruitful comments that led to the improvement of the manuscript. In the following, answers to comments are reported just below each related comment. When needed, the part of the manuscript we modified or added to the old version is reported and figures are modified accordingly. Title: I have two main concerns about the title: the main result of the manuscript is the estimation of the snow parameters rather than the variability (not clear if spatial variability, seasonal oyearly); I suggest highlighting your main achieved results. The second concern is related to “selected”: this information suggest that the authors selected the areas according to some specific characteristics (based on geology, hydrogeology, climate…) but I can’t recognize this in the manuscript. I suggest to remove “selected” According to the reviewer comment we have modified the title of the manuscript as follows: “Snowfall variation in Eastern Mediterranean catchments”. As, snow parameters’ variability, both spatial and yearly, is discussed in the manuscript, we think the above title as an appropriate one. Introduction: In my opinion, the Introduction may be summarized removing the description of methods not used in the final elaboration and giving just a brief overview of the importance of snow data and their application. Please check in the second page the paragraph since the ref. n°5. In this paragraph there are may sentences that could be removed because too vague and not related to your elaboration. Check also the two sentences starting with “for istance” “Within this study….Mediterranean” mode this sentence in the last part of the introduction “addition, the average snow coverage was found higher in January and the lowest in August” it seems to be an obvious information at our latitude. If not please detail better the relevance of this information
Synthetize the long list of possible applications and methods According to the reviewer’s comments we have modified the introduction section removing some parts in order to provide a more comprehensive introduction. Check the ref 22 We corrected the reference. “The overall goal is to better estimate and improve water resource management, based on the findings” I think your goal is to produce reliable data that may be later used to improve the water management The reviewer is right. We deleted the sentence and we added the following one: “These dataset can be used for future analysis and cros-comparison with other hydrological-hydrogeological parameters such as groundwater level and surface runoff in order to determine the influence of snowfall in the water budget variation.” The paper is structured as follow: I don’t like the description of the structure of the article in the introduction because it should be coherent with the typical structure of an article (intro, matherials and methods, results discussion and conclusion). It’s a personal consideration but I suggest to the author to evaluate if this summary is necessary The reviewer is right that the aforementioned paragraph is not adding any information to the manuscript, as the structure is straightforward, coherent with the typical structure of an article. This paragraph is deleted in the revised version of the manuscript. Study area: I suggest to the authors to check the toponyms reportend in the whole article and in the tables because sometimes they are not consistent. The brief description of the study areas is nice but you should also include some information of altitude (min-max-average) because it is a relevant issue talking about snow Study area 3: here you reported the climate data. Please include them also for the Greek areas. Table 1 Datum information is missing. Include information about the study area because only Kozani is reported in the area 2. You reported only one station per area because it was the only one available or the most relevant Figure 1 is not clear, I suggest to include the borders of the study areas, use a more visible pint for the 3 stations. I did not understand the use of the arrows and the presence of an additional point in Greece. Please check According to the reviewer comments we have add all information and made the modifications in the study areas section and revised figure 1 and table 1.
Section 3: methodology. Why it is not under the 2 mateial and methods section? The methodology section has been restructured under the Section 2. 4.1: “Snow depth derived from in situ measurements available for Mount Athos and Kozani station was employed”. Why the station Benevento was not taken in account? Unfortunately in Benevento station the snow information is not available. Figure 3 and 4 are not very clear. The study areas are separated so I suggest to make 2 detail subfigures where the reads can see in more detail the results. Also the station name in red are not visible. Figure 3 and 4 are updated in the revised version of the manuscript and a paragraph is added to comment on their results. Looking at the results in Greece they seem to be consistent. In Italy the distribution of SWE (Fig3) seems relevant only on the seaside and not on the Apennine chain, please check We thank the reviewer for the comment. The Figure is updated, due to a bug in the mapping algorithm. 4.3 The linear fit slope values show similar temporal variability for SWE and SD for the two regions: maybe 3 regions? The reviewer is right. The sentence now reads: “The linear fit slope values show similar temporal variability for SWE and SD for the three regions.” The different trends described in this section should be highlighted also in the figure 6and 7 The Figures 6 and 7 are updated in the revised version of the manuscript, according to the reviewer’s comment. The data reported in the table 2 are mean values over the 3 study areas or are the values in correspondence of the 3 weather stations? If it is the average value maybe the authors may check if there is for example a reference value of altitude which may distinguish the subareas with a significant amount of snow rather than the sections were the snow amount is almost 0 The data reported in the Table 2 are the mean values over the 3 study areas. The Table 2 is updated and it’ caption changed as follows: “Summarized the accumulative values of the snow water equivalent and the snow depth and the retrieved snow density values from the GLDAS dataset for the whole study period (1960 - 2021) as mean values of catchments.” Fig 8 the letters of the subfigures should stay close to the graphs to avoid any uncertainties. The Figure 8 is updated according the above recommendations in the revised version of the manuscript.
Discussion: I suggest to summarize the discussions focusing only on the discussion of your results. For example the sentences “the contribution of snowfall….water management strategies” (page 13) are not necessary and they don’t support your findings. The sentence is deleted in the revised version of the manuscript. “In the last decade, the higher amounts of snowfall probably contributed to the replenishment of groundwater reserves”. I’m not sure about it just looking at the figure 9 without any other details on the monitored aquifer. Beside the snow depth significally increase since 2000, the groundwater levels arise only 14 years. The small peak in 2005 seems not relevant because since 2006 the groundwater decrease again with the same trend. Maybe information about yearly rainfall or the estimation of the groundwater withdrawals may support your discussion.Why you did not provide any information also for the other two study areas? The comment of the reviewer is correct, and we totally agree. We provide only in Anthemountas basin because groundwater depletion occurs within this study area. Also, the correlation with groundwater table is depicted as future work. Obviously, such correlation requires higher effort and thus we provide only available data and only a schematic analysis of the phenomenon. We prefer to retain this information and structure in order to stimulate researchers in this direction and kindly ask the reviewer to agree with this approach. Page 14 “ In recent years….RCP 8.5 scenario” not necessary discussion. Delete or summarize We have eliminated the first sentence in the revised version of the manuscript. “These are common sources of uncertainty when dealing with satellite data that might lead to untrustworthy values of the snow parameters” how much these uncertainities affect your results? Can you give an extimantion or just a brief comment? No quantitative extensive analysis exists in literature for the satellite-derived snow parameters. The comparison with the ground based retrievals shows a good correlation of 0.65, however a slight underestimation of the satellite values. However, even if it is not a point by point comparison, this comparison shows the general good performance of the satellite snow detection. The scatterplot of the insitu data against the satellite dataset is provided in the supplementary materials. “According to the public available….10% +-5.9%.” the snow cover extent is referred to glaciers or seasonal snow cover? I did not understand how the information reported in this section may support your results. Actually, the reductions are referred to glaciers, so the paragraph is deleted. Conclusions Point 4 should be detailed in the discussion section to be achieved as achived result
We agree with the reviewer comment and we also delete point 4 from the discussion section.

Reviewer 2 Report

Dear all,

I cannot recommend the manuscript for publication because the reasons below:

11-    There is not clear information about ground measurement in a table to show data by time and date and their availability.

22-    The step-by-step information has not been provided in the method section. For example, it is not obvious whether the raw satellite data or data derived from satellite or satellite ready datasets have been used in each part of the study.

33-    The section of (4.1. Comparison with in-situ data) in the result section needed to be revised properly by using scatterplots with the mean of each data (ground vs satellite) with bias. You can find several papers about validation of the satellite data and see how the result of validation is presented.  

44-    The validation part of the work is missing in the conclusion section which has been mentioned in the introduction and it should be a part of the conclusion too. 

Based on the previous points, it can be said that the novelty of the manuscript is not clear if it is just presenting a satellite dataset of snow in a region.

Some other points need to be addressed:

-   - In figure 1, 4 locations have been selected whereas you have 3 locations.

-  -The time is 61 years but it is 51 years based on line one page 5 in the manuscript.

-  -  Figure 2, it is not clear, how the ground data and satellite are combined in the histogram. For instance, if you put the mean of each data for a specific date or month with two colours the differences would be very clear.

-     - Results in the figures 3,4 and 5 are not clear.

Best regards,

Author Response

Dear all,

I cannot recommend the manuscript for publication because the reasons below:

In the revised version of the paper the reviewer’s comments have been extensively taken into account discussing more the mentioned aspects (i.e., methodology part improved, validation results added in the conclusion part). Some text has been added about this and it is reported below into the replies to specific comments.

 

11-    There is not clear information about ground measurement in a table to show data by time and date and their availability.

A Table with all the information for the ground based measurements is added in the Supplementary material.

 

22-    The step-by-step information has not been provided in the method section. For example, it is not obvious whether the raw satellite data or data derived from satellite or satellite ready datasets have been used in each part of the study.

The reviewer is right, as the methodology part was not well readable. The methodology is rewritten and restructured in the revised version of the manuscript.

 

33-    The section of (4.1. Comparison with in-situ data) in the result section needed to be revised properly by using scatterplots with the mean of each data (ground vs satellite) with bias. You can find several papers about validation of the satellite data and see how the result of validation is presented.  

We thank the reviewer for this comment. The reviewer is right that scatterplot is a more general way of showing the correlation between two datasets, however both, scatterplots and histograms of the differences between the compared datasets are used in validation studies of satellite data (e.g., https://acp.copernicus.org/articles/23/1919/2023/ and https://amt.copernicus.org/articles/13/3043/2020/).

Below we provide the scatterplot of the results, with the regression line and the R-squared value. However, we kept the initial Figure in the revised version and uploaded the scatterplot as Supplementary materials, if the reviewer does agree on that approach.

 

 

 

 

44-    The validation part of the work is missing in the conclusion section which has been mentioned in the introduction and it should be a part of the conclusion too. 

Based on the previous points, it can be said that the novelty of the manuscript is not clear if it is just presenting a satellite dataset of snow in a region.

The reviewer is right. The validation part was missing, however added in the revised version of the manuscript as follows: “The satellite retrievals were firstly validated against in-situ retrievals for 67 common days, with a mean bias equal to –0.018 cm, with a near-Gaussian distribution, showing the good performance of the satellite snow detection.”

 

Some other points need to be addressed:

-   - In figure 1, 4 locations have been selected whereas you have 3 locations.

We thank the reviewer for pointing this. The fourth location was a typo and now the figure 1 has been updated in the revised version of the manuscript.

 

-  -The time is 61 years but it is 51 years based on line one page 5 in the manuscript.

The reviewer is right. It was a typo that corrected in the revised version of the manuscript. The sentence now is replaced by the following: “In our analysis, data were processed for the whole period from January 1960, up to December 2021”

 

-  -  Figure 2, it is not clear, how the ground data and satellite are combined in the histogram. For instance, if you put the mean of each data for a specific date or month with two colours the differences would be very clear.

Figure 2 shows the difference between the collocated ground based and satellite based values. These differences ideally should be centered to zero, with a low number of values lying around (outliers), following a Gaussian distribution.

Below, we present another form of the results, where the x-axis is the common date and the collocated ground based and satellite based values are plotted in different colors.

 

 

 

-     - Results in the figures 3,4 and 5 are not clear.

Figures, 3, 4 and 5 are updated and a paragraph is added to comment on the presented results.

 

Best regards,

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper studied the snow parameters focusing on representative geographical areas of the Eastern Mediterranean. The topic of this work fits the scope of this journal. However, there are many questions need to be addressed and the discussion needs to be improved. The following suggestions and comments should be considered during revision:

1.     The method section is not enough to explain the technology used in this work, please improve.

2.     The research significance of the work is unclear.

3.     Subsection 2.1 should explain why these three sites are chosen as the research area.

4.     What does the arrow point to in Figure 1? The Figure 1 has no legend, too small latitude and longitude, and a short explanation should be given to Figure 1.

5.     The characters and points in FIG. 3, 4 and 5 are too small to be clear, and the changes of snow cover in the study area cannot be clearly seen. Moreover, there is no detailed explanation of the changes of snow cover in FIG. 3, 4 and 5.

6.     Comparative analyses of snow cover changes in the study area need to be carried out both spatially and temporally, while satellite remote sensing and field measurements should be used for more detailed comparative analyses of the study area.

7.     Is there some in-situ measurement data can be used to test the results of satellite observed data.

8.     Generally, discussion and conclusions are simple and need to be strengthened. For improving the discussing and conclusion, I suggest the authors check carefully about some very updated works. There are many new data and achievements in glacier/snow during recent several years. Here I list some most related and latest literatures for the authors’ reference and figure out some findings in the region.

 

Niu, H., S. Kang, C. Sarangi, G. Zhang, M. Chen, Y. Zhang & H. Qin (2022) Source apportionment and elevational gradient of dissolved organic matter over the Tibetan plateau. Catena, 216.

Niu, H., S. Kang, X. Shi, Y. He, X. Lu, X. Shi, R. Paudyal, J. Du, S. Wang, J. Du & J. Chen (2017) Water-soluble elements in snow and ice on Mt. Yulong. Sci Total Environ, 574, 889-900.

Niu, H., S. Kang, W. Gao, Y. Wang & R. Paudyal (2019) Vertical distribution of the Asian tropopause aerosols detected by CALIPSO. Environ Pollut, 253, 207-220.

Niu, H.W., Kang, S.C, Wang, H.L, Du, J.K., Pu, T., Zhang, G.T., Lu, X.X., Yan, X.G., Wang, S.J., Shi, X.F., 2020. Light-absorbing impurities accelerating glacial melting in southeastern Tibetan Plateau. Environ. Pollut. 257, 113541.

Niu H.W., Kang S.C., Wang H.L., Zhang R.D., Lu X.X., Qian Y., Paudyal R., Wang S.J., Shi X.F., Yan X.G., 2018. Seasonal variation and light absorption property of carbonaceous aerosol in a typical glacier region of the southeastern Tibetan Plateau. Atmos. Chem. Phys., 18, 6441–6460, https://doi.org/10.5194/acp-18-6441-2018.

Author Response

This paper studied the snow parameters focusing on representative geographical areas of the Eastern Mediterranean. The topic of this work fits the scope of this journal. However, there are many questions need to be addressed and the discussion needs to be improved. The following suggestions and comments should be considered during revision:

We would like to thank the reviewer for his/her fruitful comments that led to the improvement of the manuscript. In the following, answers to comments are reported just below each related comment. When needed, the part of the manuscript we modified or added to the old version is reported.

 

1. The method section is not enough to explain the technology used in this work, please improve.

We thank the reviewer for this comment. The methodology section is reordered and revised.

 

2. The research significance of the work is unclear.

In the revised version we have modified introduction and discussion in order to clearly represent the significance of our study. For example, the following sentence is added in the Introduction: “These datasets can be used for future analysis and cross-comparison with other hydrological-hydrogeological parameters such as groundwater level and surface runoff in order to determine the influence of snowfall on water budget variation.”

 

 

3. Subsection 2.1 should explain why these three sites are chosen as the research area.

The study sites were chosen due to the different hydrogeological, climatological, and socio-economic characteristics. The common characteristic of the sites is the necessity to use groundwater to cover water demands. Also, snow variation information is missing from the sites. We also explain in the discussion section in the revised version of the manuscript that this work is a first step in order to study in the future the influence of snow variation in water budget of the sites.

 

4. What does the arrow point to in Figure 1? The Figure 1 has no legend, too small latitude and longitude, and a short explanation should be given to Figure 1.

We apologize for figure 1, we have updated it.

 

5. The characters and points in FIG. 3, 4 and 5 are too small to be clear, and the changes of snow cover in the study area cannot be clearly seen. Moreover, there is no detailed explanation of the changes of snow cover in FIG. 3, 4 and 5.

The Figures 3, 4 and 5 have been updated in the revised version and a paragraph is added to comment on the presented results.

 

6. Comparative analyses of snow cover changes in the study area need to be carried out both spatially and temporally, while satellite remote sensing and field measurements should be used for more detailed comparative analyses of the study area.

We thank the reviewer for this comment. In situ datasets, with general low temporal resolution, are used mainly for the evaluation of the satellite retrievals, while satellites provide data with high temporal resolution. In the future, analysis of the snow parameters of extensive datasets from meteorological stations is foreseen. Actually, this spatial analysis of snow cover changes   is planned to be future work for the study areas.

 

7. Is there some in-situ measurement data can be used to test the results of satellite observed data.

The satellite data were firstly calibrated by comparing them with ground based data from Mount Athos and Kozani station (meteorological stations, see updated Table 1), as in general, satellite resolution imposes limitations on their evaluation against point measurements. The results from the comparison with the satellite data (3.1 Section) are presented in Figure 2 (for Mount Athos). Figure 2 shows the difference between the collocated ground based and satellite based values. These differences ideally should be centered to zero, with a low number of values lying around (outliers), following a Gaussian distribution.

 Moreover, a scatterplot of the insitu values against the satellite values, showing the good performance of the satellite capture, is presented in Figure 1 in the Supplementary file. Similar results were also found for Kozani station.

 

8. Generally, discussion and conclusions are simple and need to be strengthened. For improving the discussing and conclusion, I suggest the authors check carefully about some very updated works. There are many new data and achievements in glacier/snow during recent several years. Here I list some most related and latest literatures for the authors’ reference and figure out some findings in the region.

The reviewer is right. The discussion and the conclusion part are updated in the revised version of the manuscript, with more information, (i.e., regarding the validation of the satellite retrievals with the collocated ground based measurements). Moreover, we have considered the articles provided below and we have included their findings in the introduction section.

 

Niu, H., S. Kang, C. Sarangi, G. Zhang, M. Chen, Y. Zhang & H. Qin (2022) Source apportionment and elevational gradient of dissolved organic matter over the Tibetan plateau. Catena, 216.

Niu, H., S. Kang, X. Shi, Y. He, X. Lu, X. Shi, R. Paudyal, J. Du, S. Wang, J. Du & J. Chen (2017) Water-soluble elements in snow and ice on Mt. Yulong. Sci Total Environ, 574, 889-900.

Niu, H., S. Kang, W. Gao, Y. Wang & R. Paudyal (2019) Vertical distribution of the Asian tropopause aerosols detected by CALIPSO. Environ Pollut, 253, 207-220.

Niu, H.W., Kang, S.C, Wang, H.L, Du, J.K., Pu, T., Zhang, G.T., Lu, X.X., Yan, X.G., Wang, S.J., Shi, X.F., 2020. Light-absorbing impurities accelerating glacial melting in southeastern Tibetan Plateau. Environ. Pollut. 257, 113541.-

Niu H.W., Kang S.C., Wang H.L., Zhang R.D., Lu X.X., Qian Y., Paudyal R., Wang S.J., Shi X.F., Yan X.G., 2018. Seasonal variation and light absorption property of carbonaceous aerosol in a typical glacier region of the southeastern Tibetan Plateau. Atmos. Chem. Phys., 18, 6441–6460, https://doi.org/10.5194/acp-18-6441-2018.

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors corrected all the issues I identified during my previous revision.

 

Reviewer 2 Report

Dear all,

Snow depth and snow water equivalent have been presented and satellite-derived data of snow parameters have been validated against ground measurements in three weather stations in Greece and Italy. The results of validation show good performance with a mean bias of (-0.018 cm) in the region. The snow trends are presented based on satellite-derived data which is a good way to analyse and use the results for other purposes such as hydrology studies.

Best regards,