Review Reports - Water Area Variation and River–Lake Interactions in the Poyang Lake from 1977–2021

Round 1

Reviewer 1 Report

1. The approaches used in this study should be clarified in the Introduction.

2. The significance of the study should be noted in the end of Introduction.

3. The caption of Figure 1 is too simple.

4. Annual temperature and precipitation are not mentioned in Study area.

5. Authors stated the Influence Mechanism of Lake Water Area Change in flood and dry seasons. The weight of influencing factors should be clarified.

6. To make your study more applicable, I would recommend a 5.3 section "Implications for water management in the Poyang lake".

Author Response

Reviewer 1:

Point 1: The approaches used in this study should be clarified in the Introduction.

Response 1: We sincerely accept your comments and make changes to the article：(See lines 60-67).

Point 2. The significance of the study should be noted in the end of Introduction.

Response 2: We accept your comments and make changes to the article:” (See lines 79-81).

Point 3. The caption of Figure 1 is too simple.

Response 3: We accept your comments and make changes to the article:

(a) (b)

Figure 1.（a）The Poyang Lake Basin. (b) Location of Poyang Lake in Yangtze River Basin

Point 4. Annual temperature and precipitation are not mentioned in Study area

We accept your comments and have added to the article: (See lines 97-102).

Authors stated the Influence Mechanism of Lake Water Area Change in flood and dry seasons. The weight of influencing factors should be clarified.

We accept your comments and have added to the article:” (See lines 238-244)

To make your study more applicable, I would recommend a 5.3 section "Implications for water management in the Poyang lake".

We accept your comments and have added to the article:” (See lines 358-378)

Author Response File: Author Response.docx

Reviewer 2 Report

This is an interesting study and the authors have done great work.

The paper is generally well-written and structured. However, the paper has some shortcomings regarding spelling errors and the English text.

In the attached file I have provided remarks on the text. Moderate changes are required in the English text to make the paper publishable.

Accepted after Moderate changes in English text.

Comments for author File: Comments.pdf

Author Response

Reviewer2:

Point：In the attached file I have provided remarks on the text. Moderate changes are required in the English text to make the paper publishable. Accepted after Moderate changes in English text. The paper is generally well-written and structured. However, the paper has some shortcomings regarding spelling errors and the English text.

Response 1: We sincerely accept your comments and make changes to the article

Author Response File: Author Response.pdf

Reviewer 3 Report

1. The article requires comprehensive linguistic correction. While the text is understandable, there are many minor errors.

2. There are also a lot of editorial errors concerning the text itself, including references to sources and figures.

3. The biggest doubts concern the type and quality of the data used, which limits confidence in the correctness of the results obtained.

4. I also have reservations about the description of the methods used. There are considerable uncertainties in this regard. The paragraphs on data and methods of their analysis should be significantly changed and expanded.

5. Detailed notes are added to the text of the article in the attached PDF file.

Comments for author File: Comments.pdf

Author Response

Reviewer 3

Point 1：Revision of line 11to12: Poyang Lake is the largest freshwater body of water in China.

Response 1:We sincerely accept your comments and make the changes：(See lines 10-11)

Point 2：Revision of line 17: Please be more precise. What parameter of what runoff are we talking about, what characteristics of what sediments and precipitation in what area?

Response 2: We sincerely accept your comments and make the changes: (See lines 17-19)

Point 3：There are also a lot of editorial errors concerning the text itself, including references to sources and figures.

Response 3：We sincerely accept your comments and have corrected all numerical errors.

Point 4： Revision of line 32：Considering that lakes, both fresh and salty, contain about 0.013% of our planet's water resources, the statement that they play a significant role in the Earth's hydrological cycle is greatly exaggerated.

Response 4： We sincerely accept your comments and make the changes to the article. (See lines 31-32)

Point 5：Revision of line 70：The description of the figure is definitely insufficient.1. The figure consists of two maps, which should be separately marked (for example "a" and "b") and separately described. The titles on the maps themselves will then be redundant.2. In what units is the terrain height scale on the Poyang Lake catchment map? Are these meters above sea level? If so, the lower end of the scale to the nearest ten-thousandth of a meter (1/10 of a millimeter) is a gross exaggeration.2. Why is the distance scale on the Poyang Lake catchment map in miles? Is it the Chinese mile, or is it the nautical mile, or is it something else? Doesn't the journal Remote Sensing recommend the use of SI units?3. I am very surprised by the location of "hydrometric" stations. As far as I can see, none of them is located on a river (watercourse). So what is measured at these stations? Groundwater level? How was the inflow of river water and sediment to the lake determined, if no hydrometric station was located on the watercourse flowing into the lake.4. On what basis was the watershed of the catchment (basin) of Lake Poyang determined? Is it based solely on the relief (topographic watershed) or hydrological - including the underground watershed?

Response 5：Thank you for your suggestions. We sincerely accept your comments and answer your questions.1. We have modified the image

Figure 1.（a）The Poyang Lake Basin. (b) Location of Poyang Lake in Yangtze River Basin

The topographic height unit on the map of Poyang Lake Basin is meter, and the scale unit is corrected to kilometer. 3. We have corrected the location of the hydrological stations and labeled the station names. 4. watershed of Lake Poyang determined by hydrological watershed.

Point 6: Revision of line 94：What satellite image? From what sensor and from what specific source was it obtained? Is it the image from the Corona spy mission?

Response 6：Thank you for your suggestions, which we have added to the article (See lines 115), The image was downloaded from the KeyHole lock-eye satellite.

Point 7: Revision of line 98：The description in this paragraph is clearly insufficient. Many important details are missing to assess the quality of the results obtained.1. How many hydrometric stations did the data come from and where were they located? In Fig. 1, their locations, with perhaps one exception, are outside the river network, so they are probably wrong. The map does not show, for example, the location of the measuring station enabling the assessment of the water inflow from the Yangtze River to Lake Poyang. What was the interval of the source water level (flow) measurements? Was source data used or processed (aggregated) to periodic values (monthly, annual)? 2. What exactly does the term "sediment" mean? Whether it concerns material transported in suspension or also transport on the bottom (bedload). Were measurements of sediment transport carried out at all hydrometric stations and on all watercourses flowing into the lake? What was the time interval of these measurements? Were source data used or aggregated to longer periods: monthly or yearly? 3. How was precipitation determined for the entire Poyang Lake Basin? Was it simply an average of the values recorded for individual precipitation stations, or was some method used to take into account spatial variation, such as the Thiessen polygon method or interpolation? How was evaporation determined? Was it evaporation from the free surface of the water, or so-called field evaporation? Has any method been used to account for the spatial variation of evaporation?

Response 7：Thanks to your suggestions, we have expanded the description of the data sources(See lines 121 to134). Our response to your question :1. Data were obtained from six hydrographic stations, and the locations were corrected in Figure 1. The source data is the monthly runoff data and annual sediment data published in the Hydrographics. 2. "sediment" means runoff sediment, It is the published monthly data of Hydrographics. 3. The temperature and precipitation data of Poyang Lake basin were obtained from the actual measurement data of 23 meteorological stations. Data from 23 sites were averaged for analysis.

Point 8: Revision of line 111：I would suggest to differentiate the points representing the dates of acquisition of individual satellite images depending on the sensor (MS, TM, ETM+, OLI).

Response8：Thank you very much for your suggestion. Because the data map sources are large and the extraction is consistent, the sensors are not labeled

Point 9. Revision of line 114 to 118 :What exactly does that mean? Please provide a full and clear description of the methodology used? These are vague generalities at this point.

Response 9：Thank you very much for your suggestion. For the method description has been modified (See lines 140 to150).

Point 10. Revision of line 121: Please provide the relevant source(s) describing both the Mann-Kendall non-parametric trend determination methodology and the method of identifying the date of the trend breakout. The information provided here is either insufficient or misleading.

Response 10: Thank you for your suggestion, we have added to the Mann-Kendal analysis description (See lines 152 to159).

Point 11： Revision of line 135 and 140: In my opinion (Fig. 3), after 2005 the water surface in the lake in the "wet" season did not show a clear trend.

Response 11 : Thank you for your suggestion. We have accounted for the data and the results show that the water body area does show an upward trend after 2005, but the main trend is still downward. This is mainly due to a major flood event in the whole basin in 2020, which made the water area in 2020 affect the trend of the water area after 2005. The description of waterbody area during the dry period is accurate.

Point 12. Revision of line 154：There is no consistency between the two parts of the figure, for example the red arrows mean something else.

Response 12 : Thank you for your suggestions, we have modified the picture

Point 13. Revision of line 159 to167：Is it Pearson's linear correlation coefficient? Is this relationship really linear? What does correlation > 99% mean?

Response 13 : Thank you for your comments, the relevance description has been revised：(See lines 201 to 203).

Point 14： Revision of line 171：Is it the total annual water inflow to the lake? Why are the water outflow units given in the legend of this figure and not in the corresponding figure number 5?

Response 14 : We sincerely accept your comments on the legend has been revised：

Point 15. Revision of line 177：These are the wrong units of measure! This should be, according to the axis description in Figure 7, 104 tonnes/year.

Response 15 : We sincerely accept your comments on the unit has been modified

Point 16. Revision of line 199：There is no information, preferably in tabular form, on the area and proportion of land use/land cover at the beginning and end of the analysis period (1980 and 2020). A brief description of the spatial distribution of the land would also be useful. This information could also be included in subchapter 2.1 -Study area. Please define the term "swap".

Response 16：We sincerely accept your comments and have added a 1980-2020 comparison chart. Explanation of "swap" (See lines 245 to 246).

Point 17．Revision of line 259：I believe that the way of visualizing changes in the extent of the lake on one map is not very good. I think a better solution would be to put 7 contour maps for individual dates and the eighth with overlapping them. Color fill gives false impression of ranges due to overlapping. For example, the extent of the lake on 9/14/2011 (red) appears to be very large, while the bar graph shows it to be the smallest. Besides, a bit strange, not chronological, is the order of dates in the color legend of map "b".

Response 17: We have accepted your suggestion and modified the schematic.

(c)

Figure 12. Comparison of lake water area at the end of flood season: (a) Description of lake water area at the end of the flood season; (b) Comparison of lake water area extraction results at the end of flood season. (c) Comparison of lake water area extraction results at the end of flood season.

Point 18. Revision of line 317：In my opinion, it does not result in any way from the analysis of changes in land use, at least in section 4.2.4 there is no mention of it.

Response 18: We accept your suggestion and have revised the description(See lines 395 to 396).

Author Response File: Author Response.pdf

Reviewer 4 Report

Poyang Lake is the largest freshwater lake in China and is characterized by signiﬁcant variation, but many details are not well-recognized yet. The authors have done a good job, but unfortunately it looks incomplete and raw in the current state.

It's important to discuss the research, making references to similar studies done previously and interpreting the results obtained. Previous studies that support or disagree with the present study should be mentioned. However it's stated that "previous of Poyang Lake research largely used discontinuity and a limited data period to analyze, or the analysis component was not thorough enough." No valuable researches? No relevant information in papers like:

Lan, Y-Y. Poyang lake water level change trend in nearly 60 years

Zan, Y.; Gao, Y.; Jiang, Y.; Pan, Y.; Li, X.; Su, P. The Effects of Lake Level and Area Changes of Poyang Lake on the Local Weather. Atmosphere 2022, 13, 1490. https://doi.org/10.3390/atmos13091490

Zhang, Z. et al. 2022. How does the three gorges dam affect the spatial and temporal variation of water levels in the Poyang Lake? https://doi.org/10.1016/j.jhydrol.2021.127356.

You H. et al., 2017. Effects of Water Regime on Spring Wetland Landscape Evolution in Poyang Lake between 2000 and 2010. Water 2017, 9, 467; doi:10.3390/w9070467

Han, X.; Chen, X.; Feng, L. Four decades of winter wetland changes in Poyang Lake based on Landsat observations between 1973 and 2013. Remote Sens. Environ. 2015, 156, 426–437.

Huang, F.; Yan, B.; Zhang, X.; Zhao, D.; Guo, L.; Wang, Y.; Xia, Z. Water Regime Evolution of Large Seasonal Lakes: Indicators for Characterization and an Application in Poyang Lake, China. Int. J. Environ. Res. Public Health 2018, 15, 2598.

Jiang, X.; Wang, J.; Liu, X.; Dai, J. Landsat Observations of Two Decades of Wetland Changes in the Estuary of Poyang Lake during 2000–2019. Water 2022, 14, 8.

and many, many others?

There are no references to statements like "Hydrological monitoring revealed that the interval between the wet and dry season has decreased, seasonal drought events have intensified, and floods have occurred more frequently in the last years", climate descriptions, sources of some illustrations, parts (4.2.4. Land Use Changes in the Poyang Lake), etc.

"Remote Sensing images were obtained for the Poyang Lake Basin during the dry season, as this period is characterized by cloudless skies" (lines 88-89), but " the spectral characteristics of the water images were used to set thresholds, extract lake water data, and calculate the mean area of the annual wet and dry seasons" (lines 115 - 116). Data source for wet seasons is unclear. Extraction methods are not well described. The reason for the choice does not seem obvious, possible extraction problems were not mentioned ( Wei it al., 2020 A Water Body Extraction Methods Comparison Based on FengYun Satellite Data: A Case Study of Poyang Lake Region, China). It's important to show a backstage of sentences like "after manual visual verification, the extracted water data were deemed accurate." Also, the corresponding veriﬁcation samples should be.

A physically based hydrodynamic model of Poyang Lake established the relation between the lake area and lake level (Li et al. 2016| Inter-annual variations of Poyang Lake area during dry seasons). It's important to compare resulting area trend and lake level trend from several gauge stations for verification and discussion.

There are comprehensive works on the groundwater supplement of Poyang Lake (see hydrological relationship - Fig. 4) to discuss water cycle mechanisms. Explanations for green/red arrows are absent in Fig. 4. A backflow of water from the Yangtze River to the Poyang Lake is also observed in some extreme cases (Xu et al., 2019). It's shown by small green arrows, but it's difficult to see them.

Sediment supply: wind, especially in the monsoon region, could play an important role in sediment transport in various forms. "Changes in sediment" or " Characteristics of sediment" have other meaning. Authors are talking about s supply /transport/load. See also Wang et al. Wind impacts on suspended sediment transport in the largest freshwater lake of China (https://doi.org/10.2166/nh.2020.153), Mei, X., Du, J., Dai, Z., Du, J., Gao, J., & Wang, J. (2018). Decadal sedimentation in China’s largest freshwater lake, Poyang Lake. Geochemistry, Geophysics, Geosystems, 19. (https://doi.org/10.1029/ 2018GC007439), and references therein.

Multicolored parts of Fig. 12 are hard to perceive, perhaps, it's better to split in several maps or to include outlines.

Author Response

Reviewer 4:

Point 1：Previous studies that support or disagree with the present study should be mentioned.

Response 1：Thank you for your comments，we accept your comments and have added to the article:” （See lines 68 to 82）”

Point 2： There are no references to statements like "Hydrological monitoring revealed that the interval between the wet and dry season has decreased, seasonal drought events have intensified, and floods have occurred more frequently in the last years",

Response 2：We accept your comments and have added to the article:” （See lines 49 to 53）.”

Point 3 ：It's important to show a backstage of sentences like "after manual visual verification, the extracted water data were deemed accurate." Also, the corresponding veriﬁcation samples should be.

Response 3：We accept your comments and make changes to the article: （See lines 106 to 120）

Point 4：A physically based hydrodynamic model of Poyang Lake established the relation between the lake area and lake level (Li et al. 2016| Inter-annual variations of Poyang Lake area during dry seasons). It's important to compare resulting area trend and lake level trend from several gauge stations for verification and discussion.

Response 4：We sincerely accept your suggestions and have added relevant content to the discussion: （See lines 310 to 323）.

Point 5：There are comprehensive works on the groundwater supplement of Poyang Lake (see hydrological relationship - Fig. 4) to discuss water cycle mechanisms. Explanations for green/red arrows are absent in Fig. 4. A backflow of water from the Yangtze River to the Poyang Lake is also observed in some extreme cases (Xu et al., 2019). It's shown by small green arrows, but it's difficult to see them.

Response 5：We accept your comments and make changes to the article:

Point 6：Sediment supply: wind, especially in the monsoon region, could play an important role in sediment transport in various forms. "Changes in sediment" or " Characteristics of sediment" have other meaning. Authors are talking about s supply /transport/load. See also Wang et al. Wind impacts on suspended sediment transport in the largest freshwater lake of China (https://doi.org/10.2166/nh.2020.153), Mei, X., Du, J., Dai, Z., Du, J., Gao, J., & Wang, J. (2018). Decadal sedimentation in China’s largest freshwater lake, Poyang Lake. Geochemistry, Geophysics, Geosystems, 19. (https://doi.org/10.1029/ 2018GC007439), and references therein.

Response 6：We accept your comments and We have added content and references to the discussion:” (See lines 295 to 309）”

Point 7：Multicolored parts of Fig. 12 are hard to perceive, perhaps, it's better to split in several maps or to include outlines.

Response 7：We accept your comments and make changes to the article:

(c)

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I am satisfied by the revisions. The manuscript can be accepted after English spelling check.

Author Response

Thank you for your comments，we have English spelling checked.

Reviewer 3 Report

Although the authors made a number of changes to the manuscript of the article suggested by the reviewers, many shortcomings of the first version were not removed, and new errors appeared. Most of the errors are minor, of an editorial and linguistic nature. However, there are several important doubts regarding the methodology of the analyzes and, consequently, the reliability of the results obtained. Specific comments have been added to the text of the article in the attached PDF file.

Comments for author File: Comments.pdf

Author Response

Point 1: What does it mean? I have noted the same in a previous review and there is no change. It's a mistake!

Response 1: We sincerely accept your comments and make changes to the article：(See lines 9).

Point 2. One lake or all lakes? Other than that, the same remark I made in a previous review remains: "Considering that lakes, both fresh and salty, contain about 0.013% of our planet's water resources, the statement that they play a significant role in the Earth's hydrological cycle is greatly exaggerated.

Response 2: We accept your comments and make changes to the article:” (See lines 10).

Point 3. Mistake in line 12 and 16.

Response 3: We accept your comments and make changes to the article: (See lines 12 and 16)

Point 4. 1. I look at the figure and look and nowhere do I see the designations (descriptions) a) and b).2. It is not enough to write in response to a comment in the review that the height of the terrain is expressed in meters above sea level. This information must also be included in the map legend. Also, I suggest replacing "Dem" with "Terrain height, m above sea level).

We accept your comments and make changes to the article: (See lines 82-86).

Point 5. 1. This passage contains a lot of redundant and misleading information. It would be enough to state that the analyzed image came from a specific date and was made as part of the Corona mission and indicate the appropriate source of information (website or publication). Incorrect information: (1) images were originally acquired not by the USGS but by the US Department of Defense; after their disclosure, they were transferred for distribution by the USGS, (2) in December 1967, not the first, but the fifth generation of Key-Hole spy satellites (KH 4B; https://en.wikipedia.org/wiki/CORONA_(satellite)) was in operation, (3) the processing of the original images was handled by the CIA, not NASA.2. Basic information about the spatial resolution of the image used was not provided. It was probably 1.8 m.

We accept comments and make changes to the article:” (See lines 114-120)

Point 6. What does the phrase "actual evaporation" mean? How was evaporation determined? Was it evaporation from the free surface of the water, or so-called field evaporation? Has any method been used to account for the spatial variation of evaporation?.

We accept your comments and make changes to the article:” (See lines 123), Refer to this paper for pan evaporation analysis. (1.Sun Shanlei, Zhou Suoquan, Song Jie, et al. Change in pan evaporation and its driving factors in Jiangxi Province[J]. Transactions of the CSAE, 2010, 26(9): 59－65. (in Chinese with English abstract) 2. Zhang, D., Hong, H., Zhang, Q. & Nie, R. Effects of climatic variation on pan-evaporation in the Poyang Lake Basin, China. Clim. Res. 61, 29–40 (2014).

Point 7: What exactly does the term "sediment" mean? Whether it concerns material transported in suspension or also transport on the bottom (bedload).

We accept your comments and make changes to the article: (See lines 124-132). "sediment" means the sediment content in the runoff

Point 8: Please be consistent in the descriptions. If the legend of the figure contains the wording "Landsat data", it should be analogous to "Corona data" or "KH-4B data", or vice versa if it is "High-resolution satellite data", then the second description should be "Medium-resolution satellite date".

We accept your comments and make changes to the article: (See lines 139).

Point 9: As before, I believe that "... the cited publication has no major connection with the problem that the authors of the reviewed article set themselves - a different specificity of the water reservoir, different remote sensing data."

We accept your comments and make changes to the article: (See lines 146).

Point 10: New sentence here.

We accept your comments and make changes to the article: (See lines 147).

Point 11: What threshold values were used and for what spectral ranges? This sentence is the same generalities. Please give me specifics! Was the verification manual and visual at the same time? What was manual verification? Was it done by touch with eyes closed?

The spectral features of the lake water body are set as thresholds. manual verification means person uses eyes to look at the extraction results and compare the extraction results with the original image after magnification. See if the extraction results are accurate.

Point 12: And how were mixed pixels treated, i.e. those that covered the area partially covered with water? Poyang Lake has a very complex shoreline, so there were certainly a lot of such pixels.

In the ENVI platform to extract the water bodies, the ENVI platform combined with the set threshold value to automatically extract and classify the spectral information of the image elements. Different extraction analysis methods will have different classification methods for the spectral values of the image elements, such as average, maximum, and minimum values. We extracted and verified all the extraction methods and selected the best one for retention.

Point 13: What a surprise! Previously, only "sediments" were mentioned, and now it turns out that this only applies to sand fractions. Is this a mistake or did the measurements really not take into account other fractions of sediments (clay, silt and gravel)?

We accept your comments and make changes to the article: (See lines 163).

Point 14: As in the previous review I believe after 2003 the water surface in the lake in the "dry" season did not show any clear trend.

We have accounted for the data and the results show that the lake water area in the dry season showed a decreasing trend after 2003.

Point 15: I marked it last time! What exactly does that mean? Lakebed level, spatial extent or something else?

We accept your comments and make changes to the article: (See lines 189).

Point 16: There is no consistency between the two parts of the figure, for example the red arrows mean something else. I've written about this before.

We accept your comments and make changes to the article: (See lines 196).

Point 17: Is it Pearson's linear correlation coefficient? Is this relationship really linear?

Yes, it is. we make changes to the article: (See lines 206).

Point 18: Why is the trend equation in red in this figure, with the intercept and slope in reverse order than before? In addition, in all figures of this type, the value of R2 was also given next to the trend formula, and here it is not.

We accept your comments and make changes to the article: (See lines 216).

Point 19: The "mass" of sediments, because after all, not their volume. Area of what? Water?

We accept your comments and make changes to the article: (See lines 221 and 225).

Point 20: Since it is still not known what evaporation is referred to (see the note on line 121), I propose to delete this fragment of the text and the figure associated with it.

We have already explained the meaning of evaporation in the previous section: (See lines 123).

Point 21: Again, "flood" in the legend of the figure is written with three letters "o" (floood).

We accept your comments and make changes to the article: (See lines 242).

Point 22: I believe that PCA is used in a completely wrong context here! After all, this method is not used to study relationships, but to determine the redundancy of information in multivariable data sets in which individual variables are not independent of each other. It seems to me that the PCA factor results listed in the table below make little sense when it comes to the relationship between river inflow, outflow, precipitation and evaporation. It is difficult to explain them on the basis of nature - the mechanism of water circulation processes in the catchment. Maybe the authors would like to do that? For example, why is factor 1 for evaporation positive in the wet season and negative in the dry season?

We accept your comments and make changes to the discussion: (See lines 321).

Point 23: former water area

We accept your comments and make changes to the article: (See lines 269).

Point 24: basin (catchment), The titles above the maps are redundant.

We accept your comments and make changes to the article: (See lines 267 and 274).

Point 25: I believe that the way of visualizing changes in the extent of the lake on two maps is not very good. I think a better solution would be to put 7 contour maps for individual dates and the eighth with overlapping them. Color fill gives false impression of ranges due to overlapping. One date is repeated on both maps (b and c): 2008-09-29. Due to the overlapping of the color fills, it seems as if there are two different extents of the lake.

I believe that the way of visualizing changes in the extent of the lake on two maps is not very good. I think a better solution would be to put 11 contour maps for individual dates and the eighth with overlapping them. Color fill gives false impression of ranges due to overlapping.

In the comparison of the lake water body area, there is already a numerical histogram of the lake water body area, in order to more visually reflect the difference in shape between the water area in different periods, we superimposed the comparison of the lake water area in order of size, rather than just between two dates.

Point 26: These are two sentences glued together, the first part being the equivalent of the sentence.