Assessment of Spatiotemporal Patterns and the Effect of the Relationship between Meteorological Drought and Vegetation Dynamics in the Yangtze River Basin Based on Remotely Sensed Data

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Although the authors responded my last two major comments with additional references, I don’t think they are addressed properly. However, since papers using similar approaches were published on Remote Sensing before, I may not have reason to reject this paper again.

Author Response

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Reviewer 2 Report (New Reviewer)

1) The equation of spearman correlation (Line 193) is different from the normal formulas. Please explain. 

2)The YRB belongs to different climatic zone. It is alpine climate in the west and subtrapical monsoon climate in the east, respectively. The average value of SPEI in whole YRB doesn't make sense in Fig.4.

Extensive editing of English language was required.

Author Response

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Reviewer 3 Report (New Reviewer)

Review comments

In this manuscript entitled “Assessment of the linkage between vegetation and meteorological drought over the Yangtze River Basin: spatiotemporal pat-3 tern and attribution from remote sensing data, the authors assessed the interactions between vegetation dynamic and meteorological droughts in Yangzi River basin by coupling multiple remote sensing-based vegetation and meteorological drought indices. The research seems more interesting and triggers more attention. However, based on review perspectives, this manuscript needs significant improvements relating to manuscript writing format and scientific English. The manuscript can be accepted for publication after considering a major revision.

Major comments

1.      Title: The set of title given to this manuscript lacks consistence with the objectives of this manuscript especially second objective “quantify vegetation responses to meteorological drought using multiscale data from SPEI, 109 NDVI, and SIF”.

- First, the correct quantify by analyse or examine or investigate – technically and scientifically there is no way to quantify the effects of x to y.

- Second, the authors need to change the title to reflect this objective and examining the effects of vegetation dynamics to meteorological drought.

I can suggest the author to refer to this title” Assessment of spatiotemporal and attribution of vegetation dynamics and their related effects on meteorological drought in the Yangtze River Basin based on remotely sensed data”.

 

2.      Abstract and introduction: The abstract and introduction parts are well formatted but the authors may consider some related given general comments to improve it.

 

3.      Results

-Subtitles: Sumo of subtitle are confusing

for example, 3.2.1 Meteorological drought impact vegetation degree

Is it meteorologic drought impacting vegetation dynamics or vice versa? this point is controversial to the title and objectives

 

3.2 Linkage between vegetation and meteorological drought

This word “Linkage” is not clearly scientific term, I recommend the author to replace it with “Relationship or correlation”.

3.2.2. Vegetation response to meteorological drought

This title is totally controversial with 3.2.1 and 3.2.2 and causing a big confusion to the readers. I recommend the author to match these titles with the manuscript’s objectives.

4.1 Performance differences in drought sensitivity between SIF and NDVI

This title is not clear. I suggest the authors to change it with the following" analysis of drought sensitivity to SIF and NDVI

 

4.2 Influence mechanism of teleconnection factors

The terms here are not clear, firstly, there is nothing defines mechanism in this manuscript and till end of manuscript, I didn't clearly understand the used term teleconnection. the word itself "tele" defines link between two nodes in telecommunication. did you want to say interconnection or association, or relationship? what the authors wanted to mean with this term?

 

General comments

L18: I recommend the authors to correct “interaction between…” with “The effect of vegetation dynamics on meteorological drought… “.

L21.  Put NDVI in brackets you did for SPEI and remove index after SPEI or remove the brackets and SPEI index to keep the similar contents annotation.

L26: put “and” between vegetation and drought relationships.

L28: This line is not clear, is significant correlation? if so, replace this with significant relationship with....

L29-30: What the months in brackets mean?

L31 and 32: replace the terms” link and telecommunication” with correlation and interconnection

L 34: “…and sunspots are crucial drivers in affecting…”, replace "in" with "that"

L43: “… due to a decrease in regional...”, Replace it with “…based on an increasing rate of ....”

L56. “The more popular drought indices of “Consider to delete this. Is meaningless.

L59-60. This paragraph is not clear, consider to revise

L61. …DISS and SPEI do not only involve…., Keep to correct here and add “do”

L69. delete and drought

L80. “a growing body of research...” what did the authors wanted to see with these words?

L87. “there has been…” correct with “there is a growing...”. And please check carefully the used tenses in this manuscript, there a lot of grammatical and tenses mistakes.

L96. Replace “there have been several serious drought events in the YRB.” With “Several drought events occurred in YRB”.

L153. Remove brackets.

L166.  Replace “is present in Figure 2” by “is presented in Figure 2”

L227. Replace “Meteorological drought spatiotemporal pattern” with “Spatial patterns and temporal variation of meteorological drought”

L268. This paragraph is not clear. please consider to revise

L465-468. This paragraph is too long and not even in line with the manuscript contents. please consider to revise and fragment it

L465-481. The after all declared uncertainties are logically insufficient and not relevant. please consider to calculate the uncertainties and explain well all possible uncertainties in your calculations.

L484-485. This paragraph has misunderstanding argument. There is no vegetation stress analysis in this manuscript. please consider to correct

L495-501. This paragraph is not clear, please consider to revise

 

Refer to my declared comments to the authors

Author Response

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Round 2

Reviewer 2 Report (New Reviewer)

I still think that the average of SPET in whole YRB doesn't make sense.

The English Language is good.

Author Response

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Reviewer 3 Report (New Reviewer)

I strongly recommend authors to consider correction of the section 3.2:

First, the is no difference between 3.2, 3.2.1 and 3.2.2. the are all mentioning relationship between vegetation dynamics and meteorological drought. Here I am still emphasizing that the author may break this entire section in one. just keep 3.2 and combine 3.2.1 and 3.2.2 as 3.2.

Secondary, I recommend the authors to check English grammar again and adjust the manuscript structure.

The comments are mentioned in above section.

Author Response

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This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This paper analyzed the response of vegetation to drought in the Yangtze River Basin. It’s highly valuable discussing this topic. However, it has several significant drawbacks, and the reviewer has several concerns and suggestions for the author to consider.

 

(1)    One objective of this study is to analyze the impact of drought on vegetation. This is assessed using the maximum correlation coefficients between SPEI and NDVI/SIF. However, the SPEI supplies information of both the dry and wet signals. Therefore, the results part actually discussed the response of vegetation to both the dry and wet signals, but not to the drought only.

(2)    The other objective of this study is to analyze the effect of ocean-atmosphere teleconnections on the vegetation-drought linkage. Firstly, the linkage of vegetation-drought cannot be demonstrated merely by the correlation coefficients. Secondly, this part lacks in-depth and convincing analysis though the PWC results only.   

(3)    Figure 2 is not necessary since it does not show the workflow of this study and the information has been supplied in the text. Besides, I suppose the “drought impacts on vegetation” and “vegetation in response to drought” have the same meaning in the manuscript.

(4)    What’s the meaning of “equation difference”, di, in Equation 2. What’s the meaning of a and τ in Equation 3 and 4?

(5)    How the PWC is improved? It’s not clear from the Methods part.

(6)    Line 137, lines 212-215, and Figure 3. What’s the meaning of “scale”? How to calculate the scaled SPEI? By calculating the smoothed average or average of every 3/6/9/12 months?

(7)    Lines 215-218. “Therefore, when utilizing drought indices to characterize the dry and wet conditions of the YRB, longer time scales are more effective in capturing periodic changes as compared to shorter time scales.” This sentence is meaningless.

(8)    Figure 5 and 6. Why not overlap the significance plots (right panel) on the plots of spatial distributions (left panel)?

(9)    Line 227. “These findings suggested that the YRB may become wetter in the future.” We cannot guess the future situation from the data we have now.

(10) What are the meanings of the bars, dots, and boxes in Figure 7?

(11)  Figures 9 and 10, panel b and c. There are conflicts between the panel titles and figure caption.

Author Response

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Reviewer 2 Report

This paper explore the spatiotemporal characteristics of droughts in the Yangtze River Basin using a multi-scale SPEI. Also, there is a significant relationship between vegetation and drought that varies across different vegetation types and regions. The study also found that the correlation between vegetation and drought is influenced by natural factors and human activities.  The findings can be applied to improve our understanding of the complex relationship between vegetation and drought, and develop more effective strategies for managing water resources in regions affected by drought. Additionally, the methods could be applied to other regions around the world to better understand how vegetation responds to drought in different context. However, my major and minor concerns are listed as follows. 

Major:

1. Lines 75-87: It is mentioned that large-scale climate patterns and solar activities are linked to vegetation and drought. Why PDO, ENSO and sunspot are selected? The 'growing interest (line 77)' should be explained and more comprehensive  introduce is needed for the important factors for vegetation and drought, and the reason for selecting PDO, ENSO and sunspot from them. One citation [12] is hardly enough. Maybe parts of section 4.2 should be moved to the introduction section.

2. Lines 221-234: The conclusions here need more evidence. For example, Line 227, I don't see why the trends are positive leads to the statements that the YRB may become wetter in the future. This conclusion should be supported by prediction or projection models, otherwise it may not be suitable to be mentioned here. Also, the trends calculated here should be statistically tested.

3. Lines 394-401. This paragraph discussed that vegetation respond differently to drought. However, the title of this section is the differences between NDVI and SIF indexes. This paragraph may not be suitable to be placed in this section.

4. The information in the captions of the figures are not enough.(1) In Figure 4, the meaning of the dotted lines and dashed lines should be introduced. (2) Figure 6. Significance level is needed. (3) Figure 7. It would be very helpful for readers to explain the vegetation type abbreviations in the caption. (4) Figures 9 and 10. Maybe lines 339-342 should be included in the captions.

Minor:

Line 81. The abbreviation of XWT seems unnecessary here since it is mentioned only once in the paper.

Line 176. The method used in the significance test of correlation coefficients should be introduced.

Line 266. Section 3.2.1 illustrates the statistical analyses of drought and vegetation, which does not necessary means 'impact'. The title of this section should be reconsidered.

Figure 4. 2020 in the x-axis in (c) should be corrected.

Line 438. the brackets for NDVI are unncessary.

Author Response

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Reviewer 3 Report

Dear Authors,

I agree the manuscript is very interesting and the research design is approriate. In my opinion the Authors revealed fine results confirming chlorophyll fluorescence is accurate plant indicator for finding stress conditions and environmental hazards such as drought. I have some major questions need to be concerned and included in the paper.

Section "Introduction" lines [54-58]. You wrote:
Recently, a variety of drought indices have been proposed to assess drought situations [13], such as Palmer Drought Index (PDSI) [14], Standardized Precipitation Index (SPI) [15], and Standardized Precipitation Evapotranspiration Index (SPEI) [16]. Because SPEI takes evapotranspiration into consideration, it is more suitable for assessing the effects of climatic warming on drought severity [17, 18].

What about DISS index (Drought Information Satellite System)? It is very useful index that was primarily tested and adapted for monitoring drought at national scale. Mind the results highlighted at the paper
https://www.mdpi.com/2072-4292/12/18/2944

It is worth to include in the section DISS is based on application of meteorological parameters (air temperature, precipitation) for generating HTC and multitemporal MODIS satellite data for mapping TCI across 2001-2020 years.

Among popular indices PDSI, SPI, SPEI I think DISS should be mentioned for clarification of many approaches for mapping drought with remote sensing data.

Next issue is in Introduction, lines [67-73]. You wrote:
This may be because NDVI and EVI only reflect changes in vegetation greenness rather than direct plant photosynthesis [26]. Nowadays, solar-induced chlorophyll fluorescence (SIF) has emerged as an innovative and effective variable for monitoring plant photosynthesis [12, 27, 28]. Several more studies have confirmed that chlorophyll fluorescence is directly associated with the photosynthesis of vegetation and can rapidly reflect water or heat stress [29-31]. Therefore, we applied SIF data to detect the linkage between vegetation and drought, as a comparison study with NDVI.

In my opinion, chlorophyll fluorescence can rapidly reflect to senescence (browning) phenological stages as well as carotenoid content to provide valuable insight into diagnoses of plant stress affected by drought. Please see the following papers:

https://www.sciencedirect.com/science/article/pii/S0303243419312759

while you can find confirmations of utilizing Copernicus Sentinel-2 high resolution satellite data for mapping chlorophyll fluorescence at local/country scale. It should be noted in the introduction, that there are new approaches for investigating SIF applying high/medium resolution multispectral images.

Next question is on GOSIF data. You utilized monthly compositions GOSIF data offering coarse spatial resoution, while as far as we know the extreme droughts can be appeared and disappeared withing few weeks and might be not lasting more than one month vide.

Section 2.2. Datasets [lines 148-149] Table 1.
You present SPEI ranges for classifications of drought NOT regarding land cover types presented on Figure 1. My question is:
What type of drought do you wish to analyze? Agricultural drought? Drought on forested areas /or grasslands? Please mind that different environments reflect the drought occurences diversely and there are different levels of sensivity of givent type of land cover to drought. In my opinion you should add some literature confirming the drought you investigate is general approach not regarding land cover types.

Results sections is written and described properly.

In the discussion I agree SIF is more accurate to relations with SPEI than NDVI. NDVI (and other vegetation indices) are strictly related to vegetation greenness rather than direct plant photosynthesis like SIF. However at the end of section I would suggest to add some sentences on new approaches utilizing coarse resolution remote sensing data for mapping with higher resolution (downscaling) and fusion of remotely-sensed data for investigating the environmental changes https://www.mdpi.com/2072-4292/15/3/844; https://sciendo.com/article/10.2478/mgrsd-2020-0029

Nowadays there are offered satellite data with finer spatial and spectral resolution than might be utilized for finding spatiotemporal patterns of linked the environmental conditions to vegetation https://www.sciencedirect.com/science/article/pii/S2352938522000945

Best wishes

Author Response

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Round 2

Reviewer 1 Report

Thanks for the authors’ revisions and responses. However, I think the authors might misunderstand my first two comments. These two major comments need further clarification.

 

Firstly, I definitely agree that SPEI is an effective index indicating various types of droughts. The SPEI value larger than -0.5 indicates normal situation, but not drought. The study shows the correlation coefficients between SPEI and NDVI/SIF using the whole series of SPEI values. I don’t agree with the author that the results demonstrate the response of NDVI/SIF to drought only.

 

Secondly, I may suggest separating the content into two papers focusing on the two objectives respectively. For the content focusing on the second objective, more in-depth investigation is needed. For example, I wonder why do the authors choose PDO, ENSO, and sunspot only? Why not AO? Mathematically, the PWC can be derived removing any variables. Besides, How do these elements influence the linkage of vegetation-drought? All of this is too obscure from the manuscript now.

 

Therefore, I may suggest reject but encourage resubmission of this manuscript at this time.

Reviewer 2 Report

The manuscript was significantly improved, which can be accepted after minor revision.

1. Lines 83-85. The grammar of this sentence should be checked. Either the author delete the word 'Because', or replace the word 'which' with 'they' or some other subjects. 

2. Since the 'drought' is revised into 'meteorological drought', the authors better should check the whole manuscript about this statement. For example, lines 102-103 still use 'drought'. Or they can point out that 'meteorological drought' is represented as 'drought' for simpler expression. 

3. Lines 161-162: The abbreviations of ICSU and WDS seem unnecessary here since it is mentioned only once in the paper.

4. Check the hyphen, minus sign, and en dash in the whole manuscript. For example, line 141, period 2001-2020 should be en dash rather than a hyphen; lines 197, 316 and table 1, minus sign should be used rather than hyphens.

Reviewer 3 Report

Dear Authors

Thank you for your clarifications. I am happy to accept the paper in present form. Wishing you a lot of citations.