The Spatio-Temporal Evolution Characteristics of the Vegetation NDVI in the Northern Slope of the Tianshan Mountains at Different Spatial Scales

Round 1

Reviewer 1 Report

The authors have employed NDVI3g (with varying spatial resolutions) to determine changes in vegetation over the 35 years (1982-2015) based on the Mann-Kendall test. The applied method is a common practice for determining long-term changes in vegetation and hence, as such there is no novelty in methods. However, understanding such changes in regions definitely important. As per the current form, the manuscript has some issues which need to address. The specific comments are given below. Accordingly, a major revision of the manuscript has been recommended. 

Major Comments:

1)      Abstract: The first sentence is very long (L10-14). Rewrite . Moreover, critical findings are missing like which type of vegetation is changed over the 35 years. 

2)  Introduction is not properly contextualized. It is only about NDVI-related studies. The greening and browning studies have done also using LAI. which is missing completely. Moreover, methods are not contextualized related to such long-term monitoring such as Mann-Kendall, Sens slope, etc…

3)      Objective of the study is not clearly defined

4)      Novelty of the study is not clearly defined

5)      Section 2.1: Climate and soil are not introduced for the study area

6)      2.3 rename as Methods

7)  Why was only annual-based NDVI (L146) employed for the Mann-Kendall test? Why not inter-seasonal analysis not considered?

8)      Figures 3, 4, and 5: I found that even over desert regions many pixels show positive trends. Despite having desert, how NDVI is showing up? I suggest removing such pixels which are unwanted by masking. 

9)      The statistical significance level has not been tested for Figures 3, 4, and 5.

10)   Table 2. The caption says in vegetation types. However, even over the desert the % of trends shown? Something wrong with the % calculation as I don’t find 100% area per calculation. Recheck the entire Table 2. What classes are under Other

11)  I don’t find a linkage between the percent vegetation changes (as estimated by trends) and its corresponding climate drivers. The role of climate is missing both in Intro and results and discussion.

12)   The discussion section needs improvement. Before the statement of Ren et al. [38] studied in the discussion, add similar studies conducted over the Tibetan plateau and India. For example, 

 Chen, C., Park, T., Wang, X., Piao, S., Xu, B., Chaturvedi, R.K., Fuchs, R., Brovkin, V., Ciais, P., Fensholt, R., Tømmervik, H., Bala, G., Zhu, Z., Nemani, R.R., Myneni, R.B., 2019. China and India lead in greening of the world through land-use management. Nat Sustain 2, 122–129. 

Parida, B.R., Pandey, A.C., Patel, N.R., 2020. Greening and Browning Trends of Vegetation in India and Their Responses to Climatic and Non-Climatic Drivers. Climate 8, 92. 

Sarmah, S., Jia, G., Zhang, A., 2018. Satellite view of seasonal greenness trends and controls in South Asia. Environ. Res. Lett. 13, 034026.

 13)   Discussion needs improvement by including limitations of the study and future scope

14)  There is high rainfall in the area, and various factors create an environment suitable for vegetation growth. Add reference here

 

15)  Conclusion needs to focus on major findings which are missing. For instance, which type of vegetation is changed over the 35 years.  

Author Response

感谢大家对这篇稿子的建议。具体修改请参考附件。

Author Response File: Author Response.pdf

Reviewer 2 Report

It would be nice to add a figure with shapes of trends, not only about their proportion.

The colours on figures about NDVI change trend spatial distribution are very similar.  So, even a strong positive trend is difficult to split from a strong negative one. Please make the figures more bright and in different colours, like Figure 2. Vegetation types in the study area.

Author Response

谢谢您的建议，我们已经做了相应的修改，请看附件

Author Response File: Author Response.docx

Reviewer 3 Report

Based on GIMMS NDVI data, this paper discusses the spatio-temporal evolution trend of vegetation NDVI at different spatial scales. In view of the existing problems in this paper, the following suggestions and suggestions are put forward:

(1) The introduction of research methods is not comprehensive, such as MVC, etc., and the introduction is not detailed enough, such as M-K.

(2) The spatial resolution is resampled from 8km to 0.5km and 1km, that is to say, the low resolution is resampled to the high resolution. This method has its own problems, so the results are meaningless.

(3) There is no obvious difference between Figure 2, Figure 3 and Figure 4. After all, the same data is obtained by resampling, and the slight difference is also caused by resampling.

(4) It is suggested to use MODIS data with a resolution of 0.5km to carry out relevant research in this paper.

Author Response

感谢大家对这篇稿子的建议。具体修改请参考附件。

Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript used the Mann-Kendal method to analyze the spatial-temporal evolution characteristics of vegetation NDVI on the NTSM from 1981 to 2015 and furthermore to explore the consistence of the interannual variation trend of vegetation NDVI at different spatial scales. The study is meaningful for the spatial analysis always suffers problems involving scales. However, there are some issues that need further improvement, which are as follows.

1. The authors use the Mann-Kendal method to identify the consistence of the spatio-temporal evolution on NDVI at different spatial scales. In my opinion, The Mann-Kendal method just explores the general trend of a series. The method may be not enough to illustrate the evolutionary consistence at different spatial scales. Could authors further supplement the analysis with other methods?

2. Could the authors further explain how resampling is performed with the data from a spatial resolution of 8 km to 1 and 0.5 km. What is the resampling algorithm used?

Author Response

Thank you for your suggestions on this manuscript. Please refer to the attachment for specific revisions.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

After reading the revised manuscript, I find that the authors have addressed my queries. However, their answers are reflected in the response sheet and not in the manuscript. So I have minor suggestions as below.

 1.      Figure 6 not cited as well as not useful. It should be given as raster map showing level of the p-value (0 to 1)

2.      Point 10: Authors indicated

"Desert vegetation refers to the sparse vegetation type composed of xerophytic or ultra-xerophytic semi-trees....". This information is not integrated inside ms.  

 

3.      Under the Limitation of the study in the discussion section, add some information from point 11 related to climate drivers. 

Author Response

Detailed responses are in the attached documentation.

Author Response File: Author Response.pdf

Reviewer 3 Report

The author's revision of the paper has perfectly explained the problems I raised.

Author Response

Response to Reviewer 3 Comments

Dear editor and reviewer：

Thank you very much for the expert reviewers who took the time to review our revised manuscript and affirmed our revision. Thank you again for your comments and suggestions. We will work harder in the future. Wish you a smooth work

Reviewer 4 Report

The manuscript have been improved, but there are still some questions confusing me. Could the authors make it clearer?

The authors argued that the focus of the manuscript is not to explore the method of scaling down and that the method adopted is relatively simple. As I known according to the manuscript, the spatial resolution of the data from the source is 8 km, and they are resampled to resolution of resolution of 1 and 0.5 km, right? Although down scaling method may be simple, but the specific method used is neither given nor even mentioned in the manuscript. Therefore, I cannot judge the meaningful of comparing the interannual variation trend of vegetation NDVI at different spatial scales. For example, using the nearest resampling algorithm makes little sense, so does the bilinear. Could the authors give some more information?

Author Response

Response to Reviewer 4 Comments

Dear editor and reviewer：

Thank you very much for the expert reviewers who took the time to review our revised manuscript. Your comments and suggestions are greatly appreciated. We have made targeted revisions and further polished the manuscript language. Please find my item-by-item responses below, and my corrections in the resubmitted manuscript.

We look forward to hearing from you regarding our submission. We would be glad to respond to any further questions and comments that you may have.

 

Point 1: The authors argued that the focus of the manuscript is not to explore the method of scaling down and that the method adopted is relatively simple. As I known according to the manuscript, the spatial resolution of the data from the source is 8 km, and they are resampled to resolution of resolution of 1 and 0.5 km, right? Although down scaling method may be simple, but the specific method used is neither given nor even mentioned in the manuscript. Therefore, I cannot judge the meaningful of comparing the interannual variation trend of vegetation NDVI at different spatial scales. For example, using the nearest resampling algorithm makes little sense, so does the bilinear. Could the authors give some more information?

Response 1: Thanks to the experts for their advice, we have added the detailed process of data processing in the part of the revised manuscript methodology.

Round 3

Reviewer 4 Report

Most of the relevant questions have been answered by the authors. However, there are still some issues that should be noted. Some specific comments are as follows.

1. The authors should confirm the meaningful of downscaling resampling with the cubic convolution method. Resampling is different from interpolation. Usually, valid downscaling method is not just resampling.

2. It might be more appropriate to place the section “2.3.4. Data processing” at the beginning of the “2.3. Methodology”, i.e. “2.3.1. …”.

Author Response

Please refer to the attachment for specific modification.

Author Response File: Author Response.pdf