Quantifying the Effects of Snow on the Beginning of Vegetation Growth in the Mongolian Plateau

Round 1

Reviewer 1 Report

Dear authors,

Under the background of global climate change, a series of changes have also taken place in the climate of the Mongolian Plateau. Studying the relationship between snow cover and vegetation growth is of certain practical significance for scientifically understanding the regional response characteristics of snow cover, maintaining ecosystem stability and improving vegetation productivity.

1. It is suggested that the title clearly express "the beginning of vegetation growth" so as not to be confused with crop growth period, etc.

2. Vegetation growth is affected by many factors. Besides precipitation (snowfall), ecological factors such as temperature play a crucial role. Under the background of climate change, not only the snowfall on the Mongolian Plateau has changed, but also the temperature. How to eliminate the influence of temperature and other factors on the vegetation growth change on the Mongolian Plateau is the scientific basis of this paper, which needs further analysis and demonstration. It is particularly important to emphasize that biological temperature is an important driving factor for the change of vegetation phenology. Talking about the change of vegetation phenology without biological temperature has great limitations. It is suggested to further condense the thinking and rationally express the relationship between snowfall and vegetation growth.

3. Plant phenology directly reflects the impact of climate change and is the key to vegetation dynamic simulation. The application of remote sensing and related methods in the study of vegetation change on the Mongolian Plateau requires a comprehensive analysis from the aspects of regional physical and geographical characteristics, zonal distribution of vegetation, etc. The simple and superficial expression in this paper fails to go deeper into the closer relationship between vegetation change and related factors, and only stays at some observed phenomena. It is suggested to highlight the correlation between regional hydrothermal coupling relationship and different types of vegetation to clarify the process and mechanism of snow cover and vegetation change.

4. The vegetation of the Mongolian Plateau is divided into broadleaf forest, coniferous forest, meadow steppe, typical steppe, desert steppe, etc. It is suggested to further elaborate the spatial characteristics and the background of water and heat conditions of various vegetation types, and the changes under the superimposed snowfall elements in the past 20 years. Phenology is a long-term evolution process, as is climate. Generally, analysis should be made on the basis of 30 years or longer time series data, which is more in line with the subject characteristics and practical situation.

5. In this paper, the scientific problems of the research on snow cover and different types of vegetation change on the Mongolian Plateau are not clearly sorted out. The description is mostly based on the literature of Chinese scholars, and the systematic description of the relationship between snow cover and vegetation based on phenology, meteorology, biology, ecology and other disciplines from a global perspective is lacking.

6. Some points need to be discussed. (1) As in conclusion (1) "Different vegetation types in the whole study area undergo similar changes of SCFWinter with a slow downward trend”. The theoretical basis of "trend" is not sufficient. At the same time, the analysis and argumentation of conclusion (3) and conclusion (4) in the paper are relatively plain. It is suggested to further combine monitoring data, remote sensing method or model simulation method to conduct more accurate analysis and draw a convincing conclusion.

7. Be careful with some expressions. (1) It is suggested to standardize the graphic expression. (2) Data sources and reliability need to be analyzed. (3) The reference format shall be verified one by one and expressed in accordance with the standard format. (4) There are certain differences in NPP accounting by different methods, so it is suggested to properly explain the rationality of this method in the research area and corresponding problems and the credibility of the research results.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

General review:

This study mainly focuses on the impact of changes in snow cover on the Mongolian Plateau on vegetation changes. The study used the modified Carnegie Ames Stanford Approach (CASA) model was to estimate start of growing season NPP (SOSNPP) for different vegetations over the Mongolian Plateau from 2001 to 2019 and explored the relationship with snow cover change. It has certain research significance. However, there are several main problems as follows for publish. The topic of manuscript is to quantify the impact of snow cover on the growth period. However, the whole introduction first mentions vegetation change and NPP. It should start with snow cover change and talk about the possible impact of snow cover change on vegetation. Significant literature on changes in snow cover is lacking in the manuscript. (Please check “Zhao Qin et al., Snow Cover Phenology Change and Response to Climate in China during 2000–2020” add some research by Chinese Scholars). In addition, the study used MOD10A1 data, in which the influence of clouds is very large in study area. Therefore, the statistical snow phenology is not accurate, so the conclusion is not accurate. The author did not explain this, and it is recommended to use related cloud-free products (Hao et al. Development and validation of a new MODIS snow-cover-extent product over China. Hydrology and Earth System Science, 2022, 26, 1937–1952.).

 

Other review:

1. The author elucidated the mechanism of the effect of snow phonological parameters on SOSNPP for different vegetations, so need to add different vegetation types in 2.1 in the text.

2. Line162-163: The author mentioned “Snow melt date (SMD) refers to the first day of five consecutive days with snow cover fraction (SCF) in a hydrological year”， does it mean“Snow melt date (SMD) refers to the first day of five consecutive days with SCF >0 in a hydrological year”?  If yes, whether the “first day of five consecutive days”  is the snow start date or the snow melt date (SMD). The author need to further understand and interpret the parameter definitions and determine whether the calculations are correct.

3. Line 163-164: Why is the hydrological year from September 1 of the current year to April 30 of the next year? The usual definition is a whole year, not a fraction of a year as such. Otherwise, it is not a hydrological year, but a snow cover period.

4. The study mentioned “the mean and maximum SMDspring values are 118 and 215 days”, what season is equal to or less than 118 days?

5.“Growing season SOS_NPP” and“Snow melt date (SMD)” SCM refers to the day of the hydrological year, which is a point in time, not a time period， so in the formulation, it is suggested that the unit is not days, but that it be represented by the day of the year (DOY). You need to modify the relevant expressions in the figure and the text. Such as “Line 277-279”, “Line 308-310”, etc.

 

6. In the discussion, it is recommended to add sub-headings to make the discussion logic clearer.

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear Authors,

(1) According to the first review opinion, you have made a comprehensive revision. You now submitted the revised draft of remotesensing-2169085-peer-review-v2, which has improved the obvious defects of the first draft and improved the quality of the paper to a certain extent.

(2) It is suggested that you further standardize the format expression.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The study used MOD10A1 data, in which the influence of clouds is very large in study area. Therefore, the statistical snow phenology is not accurate, so the conclusion is not accurate. The author still did not explain the possible impact of the cloud snow cover products (such as, MOD10A1) on phenological results. There are two kinds of cloud-free snow cover products can be used for your study area. One is MODIS NIEER snow cover products, the other one is MOD10A1F from NSIDC. Both products are better than MOD10A1.

The NIEER MODIS snow-cover-extent (SCE) product coverage is as follows.

E: 142.00

W:  72.00

S:  16.00

N:  56.00

MOD10A1F product is global coverage. The current results are not reliable until better data are used.

Author Response

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Author Response File: Author Response.docx