Novel Index for Hydrological Drought Monitoring Using Remote Sensing Approach: Standardized Water Surface Index (SWSI)
Round 1
Reviewer 1 Report
An interesting new drought index method using analyzed satellite imagery. A very well written and presented paper. One limitation I did not see discussed by the authors is related to the sensitivity of drought correlated surface area for time-lapsed satellite images. By that I mean, if the reservoir (tank) being analyzed has steep or near vertical slopes with depth, the surface area changes may be small, even though drought is clearly under way if depths change significantly. It would be illuminating if the authors could comment on the variation of the volume-surface area-depth values for the 5 reservoirs (tanks) analyzed. That is of course assuming that the data is available. If however the satellite imagery clearly shows surface area changes over time (months), then the methodology is clearly more applicable. However, the methodology should be applicable to most shallower reservoirs.
My only other comments and editorials are as follows:
Lines 50-51: There should be consistency in capitalization of the different types of droughts. Sometimes they are capitalized, other times in the text they are not.
Lines 113-115: A clarification note here would be helpful in addressing reservoirs where depth-surface are relationships are limiting (e.g., cylindrical tanks will show same surface area for different depths).
Line 134: “..which Locates…” to “…is located….”.
Line 161: In Table 1, a column of depth ranges (if available) for each tank would be helpful.
Lines 555-557: The title could be clarified. The “Green bars…” seems to merge with the prior definitions.
Line 602: “..reviled” to “revealed”.
Author Response
We sincerely thank Reviewer 1 who took their time and effort in reviewing our article and providing valuable and important suggestions and comments that helped us to improve the quality of the manuscript. Please find our point-by-point responses for the relevant comments/suggestions made by Reviewer 1. As authors, we believe that our responses are orderly and acceptable. If you need more information, please let us know. Thank you again.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors presented a novel index for Hydrological Drought Monitoring using Remote Sensing Approach named Standardized Water Surface Index (SWSI). As for me, the paper sounds good and can be improved by considering and applying the above comments.
1) Remote Sensing offers efficient tools for drought monitoring, especially in locations lacking reliable and consistent in-situ multi-temporal datasets. In this area, many drought indices have been proposed by researchers. Temperature-Vegetation-soil Moisture-Precipitation Drought Index (TVMPDI) is a recent and compatible drought index that includes factors such as land surface temperature, vegetation status, soil moisture, and precipitation. Please cite the paper TVMPDI and clarify the differences between TVMPDI and the proposed index.
TVMPDI :https://doi.org/10.1016/j.asr.2021.08.041
2) another gap in this paper is comparing the index results with one or more conventional remote sensing drought indices, including VCI, TCI, VHI, TVDI, MPDI, and TVMDI. Please compare the prsented index with at least one of the indices in a separate section.
3) If you use the precipitation station data, please evaluate the proposed index with these. This is a remote sensing aim and we want to know the accuracy of remote sening analysis with the field data.
4) In water surface extraction with SAR satellite data, the simple threshold can not be appropriate for all the study areas; please clarify that. This is very important, and this can be reported as a limitation of the presented research. For example, suppose the study area included a lot of moisture area. In that case, these can be considered as water bodies as false alarms and reduce the efficiency of the proposed index. Please clarify this limitation in the discussion index.
http://dx.doi.org/10.1029/2019WR025192
5) which polarization of the SAR images were used for water body detection? This is another limitation and can be consider for future work. Please read the paper about water body detection from dual/quad polarimetric SAR images.
https://doi.org/10.3390/w11122454
6) We can download the Landsat and Sentinel 1 images from GEE; why do the authors use another platform for downloading them? If the author wants to have a consistent method, they should use one platform for downloading data, which in this case, GEE, can be employed for downloading all of the data the author used.
7) Another limitation that can be a benefit to use for future work is DEM. DEM can be considered for accurate water body detection and use for one of the factors in the presented index.
Author Response
We sincerely thank Reviewer 2 who took their time and effort in reviewing our article and providing valuable and important suggestions and comments that helped us to improve the quality of the manuscript. Please find our point-by-point responses for the relevant comments/suggestions made by Reviewer 2. As authors, we believe that our responses are orderly and acceptable. If you need more information, please let us know. Thank you again.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
All of my concerns were well addressed.
