Areas with High Fractional Vegetation Cover in the Mu Us Desert (China) Are More Susceptible to Drought

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript ID land-3860250: “Areas with high fractional vegetation cover in the Mu Us Desert (China) are more susceptible to drought” submitted to land as an article.

 

The purpose of this article is to assess the susceptibility of the Mu Us Desert (China) to hydrometeorological drought by analyzing the maximum correlation coefficients (MCC) derived from the spatiotemporal relationships between fractional vegetation cover (FVC) and estimates of the standardized precipitation evapotranspiration index (SPEI).

 

It aims to propose a method to evaluate the impact of drought stress on ecosystem stability, with findings applicable to planning and managing vegetation cover in arid and semiarid regions globally.

 

The article addresses relevant issues and has the merit of conducting a long-term assessment (2003 to 2022).

 

The materials and methods are well described. The spatial and temporal statistical analysis is based on robust and properly executed procedures.

 

On the other hand, the article ends up being lengthy due to the repetition of already established information. This aspect is particularly evident in the results and discussions, with data presented repeatedly in figures and tables and presented in detail in the text. A careful review of the writing could make the article more concise and objective.

 

Overall, the article, citations, and references comply with the journal's standards.

 

The content of the article is relevant, and the article is written in accordance with English language standards.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addresses a relevant question in the context of climate change and ecological restoration: how fractional vegetation cover (FVC) modulates vegetation response to drought in an arid region. The methodology is generally sound, with good use of multiscale drought indices (SPEI) and nonparametric correlation techniques. The manuscript is well structured and presents a comprehensive analysis. However, to further strengthen the quality and impact of the work, I would like to offer a number of minor comments that should be addressed before it can be considered for publication.

General comments

C1. The main concern is that the novelty of the research is not fully clear. The manuscript lacks a clear and compelling statement about the originality of the study.

C2. What are the advantages and disadvantages of this study?

C3. What are the major contributions of this study? should be carefully mentioned in the discussion section.

C4. In general, all figures need to be improved in terms of size and quality; they are not clearly visible.

C5. Please, look at your Discussion, is there a real comparison to other researchers of your results?. It is necessary to carry out a thorough comparison, I recommend to include some relevant references, in order to improve the discussion on the novelty of your study, comparing to the others.

*The answer to these questions should be reflected in the manuscript*

Specific comments

Line 41-54: The authors should explicitly state the research gap: most previous studies focused on linear relationships or indices such as NDVI, without systematically analyzing the maximum drought effect at different time scales and stratified by FVC. This is the innovative contribution of the work and should be stated more clearly.

Line 59: I would expect to see “In one hand” before it.

Line 59-65: Mention the advantage of SPEI over SPI and PDSI in semi-arid regions where evapotranspiration plays a key role.

Line 66-81: The authors should explicitly connect how FVC improves the limitations indicated by the authors.

Lines 106-111: It is suggested that regions with higher FVC may be more vulnerable. The concept of Vegetation Carrying Capacity of Soil Water (VCCSW) should be explicitly defined here to prepare the reader for the results/discussion.

Line 141: Only 9 weather stations were used for 39,507 km², interpolated with IDW. This can generate spatial artifacts. Justify why IDW was chosen over kriging. Include cross-validation (MAE/RMSE) to give confidence in the interpolation.

Line 146: Filling in missing data with “same month average” smooths the series and underestimates drought extremes. This method can smooth interannual variability. Justify or use a more robust temporal interpolation method.

Line 175-190: Calculating FVC with global 5–95% percentiles may introduce biases when mixing cover types. An alternative would be to calculate thresholds by cover type or validate with independent values. In addition, the maximum FVC range is cut at 70%, which may underestimate areas of higher forest density.

Line 199: Thornthwaite is used for PET. In semi-arid areas, it tends to underestimate evapotranspiration, as it does not include radiation or wind. The authors should justify this and discuss the uncertainty compared to Hargreaves or Penman-Monteith.

Line 230-237: The calculation of SPEI at 1, 3, 6, 9, and 12 months is adequate, but it should be explained whether time lags were evaluated in the correlation with FVC.

Lines 290-293: The definition of significance thresholds for correlations for the reported critical values (0.379 and 0.515) seems low; they should be justified.

Line 294: The use of IQR is correct and should be complemented with additional robustness measures and an MCC frequency histogram.

Line 331-332: The increase in FVC (6% per decade) is well reported, but it would be useful to accompany it with confidence intervals.

Line 342: Include a supplementary map showing the spatial trend of FVC (β) with significance classes.

Line 362-363: A Pettitt or structural break test would reinforce the observation of the change in trend in 2013. Apply.

Line 427: In crops, if there are irrigation areas, this factor may decouple the drought signal. It would be important to at least discuss this.

Line 433: The strong negative correlation in sandy soils in August–October should be discussed (possible senescence, late precipitation, or NDVI noise signal).

Line 504–519: I suggest reinforcing the argument with additional references to lag effects in semi-arid ecosystems.

Line 560: The concept of Vegetation Carrying Capacity of Soil Water (VCCSW) appears for the first time in the Discussion, as if it were a derived result, but in reality, it was not introduced or justified in the Methodology nor was it proposed as a hypothesis in the Introduction. This creates a problem of structural consistency. The authors should correct this.

Line 565: This is not the correct way to cite.

Line 613: Cite the source of the figure.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript tackles a relevant and interesting topic, and I believe the dataset you present has the potential to contribute to research on vegetation monitoring and land management. That said, several aspects need to be clarified or expanded before the paper can be considered for publication.

In the introduction, the general context is well established, but the novelty of the study is not entirely clear. It would be useful to explain more explicitly what gap in the literature this work aims to fill and to support this with a few additional, recent references. The methods section would also benefit from more detail, especially concerning how “high vegetation fraction” was defined and validated. Including information on thresholds, data resolution, and accuracy assessment would strengthen the transparency of your approach.

The results are currently quite descriptive. Adding more quantitative summaries in the form of tables or concise statistics would help readers grasp the main findings more quickly. The figures should also be improved for clarity and readability. In the discussion, there is some repetition, and the international context could be developed further; a closer comparison with other studies would highlight better how your results fit into the broader literature. The conclusions are somewhat long and would gain impact if they focused more directly on the key messages.

Overall, this is a promising study, but I recommend a major revision so that the results and contributions are presented in a clearer and stronger way.

Comments and Suggestions

This manuscript deals with an important topic, but several sections need further clarification and strengthening. Below I highlight some areas where the paper could be improved with concrete examples:

Introduction

The general context of vegetation monitoring is outlined, but the novelty of the study is not entirely evident. For example, it is not clear how your approach differs from previous work using NDVI or fractional vegetation cover in Mediterranean or semi-arid regions (e.g., X et al. 2021; Y et al. 2022). You could strengthen this section by explicitly stating what gap you are addressing (e.g., “few studies have combined long-term remote sensing data with high-resolution validation in this specific region”). Also, some references are quite dated; incorporating more recent studies would reinforce the relevance.

Methods

The description of how “high vegetation fraction” was defined remains vague. For instance, what threshold values were used to distinguish “high” vs. “low” vegetation cover? Were these thresholds derived from the literature, empirical data, or a statistical distribution? Similarly, more information on the validation is needed: how many field plots were used, how they were distributed, and what accuracy metrics (e.g., overall accuracy, kappa, RMSE) were obtained. Without these details, it is difficult to assess the robustness of your classification.

Results

At present, the results are mainly descriptive. For example, you state that certain areas show “higher vegetation fraction,” but this would be much clearer with quantitative summaries (e.g., percentage of area in each category, changes over time, average values with standard deviations). Figures could also be improved: the legends are sometimes hard to read, and the maps could use consistent scales and color schemes. A table summarizing the main values by region or period would be very helpful.

Discussion

Some parts of the discussion repeat what has already been said in the results, while other aspects remain underdeveloped. For example, it would be useful to compare your findings with similar studies in other Mediterranean mountain regions, or to discuss more explicitly the possible ecological or land-use drivers of the patterns you observe. This would place your results in a broader scientific context and highlight their implications.

Conclusions

This section currently restates much of the discussion. It would gain impact if shortened to two or three strong take-home messages. For instance: (1) what your analysis reveals about the dynamics of high vegetation fraction in the study area, (2) how your method contributes to monitoring, and (3) what the main implications are for land management or conservation.

Comments on the Quality of English Language

English is generally understandable but could be polished to improve clarity and flow. A professional language revision would help make the manuscript more precise and accessible to an international readership.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The revisions made to the manuscript noticeably strengthen the paper.

• Abstract and Introduction

The additions broaden the scope and highlight the international relevance of the study, placing it clearly within the context of planning and management in arid and semi-arid regions.

• Materials and Methods

The inclusion of further details on data sources, the calculation of SPEI, and the statistical procedures enhances the clarity of the methodology and improves the reproducibility of the work.

• Results and Discussion

The expanded discussion, particularly the consideration of external factors and the varying responses of ecosystems, enriches the interpretation and provides a more balanced and ecologically grounded perspective.

• Conclusions

The stronger focus on practical implications and on the transferability of the findings underlines the applied significance of the research.