Spatio-Temporal Variation and Future Sustainability of Net Primary Productivity from 2001 to 2021 in Hetao Irrigation District, Inner Mongolia

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is interesting, it has potential for readers, but it needs to be significantly improved. The figures must be completed with a consistent text that leads the reader to understand the spatio-temporal variability of the NPP - now they are just general ideas, without data support.

Do not use abbreviations in the title (not all readers of the manuscript understand the domain).

Explain abbreviations where they are first used. For example NPP (now the explanations are only on the r. 108 and 151) decide when to use the full name or only the abbreviations

r. 54 add references (the list of references must be completed with international literature - the NPP issue was not addressed only in Asia)

The introduction must be partially rewritten (r102-119) it is a combination between the study area and methodology

At the end of the introduction, state very clearly the purpose and objectives pursued

2.3.2 Hurst index - must be improved

The quality of the figures must be improved 1, 5-8, 10, 11 the text is very small and is not visible. The resolution of the images must also be increased

For r 127-131 all information are not available on the figure 1 – if are relevant add to figure

R 217-220 please explain the context for 2004-2019) now explanation is very simple (figure 2-4 didn't explain the variation of the NPP)

For figures 2-4, change the direction of the years on the OX axis to make it easier to understand

Subchapter 3.1. significant improvement must be completed as well as 3.2

Subchapter 3.2 is very general and does not explain the spatio-temporal variability of NPP

R338-340 the information is repeated (they are also in the methodology section)

The entire Results section needs to be significantly improved and completed. Currently, the text only explains the figures.

Add a discussion section where you can compare your results with similar studies. Show the limits of the study and future research directions.

Correlate the results and conclusions section with the purpose and objectives that you will go through in the introduction

Currently the conclusions are not very clear - 399-402 ("non-significant increase" and "decreasing trend in the future NPP changes")

The last lines should be relevant to the study but not to the conclusions "analyze the driving factors influencing NPP changes and elucidate the response mechanisms of NPP"

Author Response

Comment # 1: The manuscript is interesting, it has potential for readers, but it needs to be significantly improved. The figures must be completed with a consistent text that leads the reader to understand the spatio-temporal variability of the NPP - now they are just general ideas, without data support.

Response: We appreciate that you are interested in our research work. We took these comments seriously and responded to all comments carefully. Details of all changes we made are shown below. The modified parts are highlighted in the revised manuscript.

We have provided sufficient descriptions of the explanatory parts of the figures, leading the reader to understand the spatiotemporal variability of NPP. The modified parts are highlighted, as shown in the explanatory parts of each figure in the revised manuscript.

Comment # 2: Do not use abbreviations in the title (not all readers of the manuscript understand the domain).

Response: Thank you for your reminding. We have changed the abbreviations in the title to the full name.

Comment # 3: Explain abbreviations where they are first used. For example NPP (now the explanations are only on the r. 108 and 151) decide when to use the full name or only the abbreviations.

Response: Thanks for your reminding. We have carefully checked and revised the abbreviation of NPP in the revised manuscript to determine when to use the full name or only the abbreviations.

Comment # 4: r. 54 add references (the list of references must be completed with international literature - the NPP issue was not addressed only in Asia)

Response: Thank you for your constructive suggestions. Relevant international literature has been added in lines 471–477 in the revised manuscript.

Comment # 5: The introduction must be partially rewritten (r102-119) it is a combination between the study area and methodology. At the end of the introduction, state very clearly the purpose and objectives pursued.

Response: Thank you for your constructive suggestions. We have made modifications in the introduction section in lines 102–132 in the revised manuscript.

Comment # 6: 2.3.2 Hurst index - must be improved

Response: Thank you for your constructive suggestions. We have provided a more detailed introduction to Hurst index in lines 203–218 in the revised manuscript.

Comment # 7: The quality of the figures must be improved 1, 5-8, 10, 11 the text is very small and is not visible. The resolution of the images must also be increased

Response: Thanks for your suggestions about the figures. We have made modifications to the text in figures 1, 5-8, 10, and 11, and changed the exported figures to tif format to improve the resolution of these figures.

Comment # 8: For r 127-131 all information are not available on the figure 1 – if are relevant add to figure

Response: Thank you for your constructive suggestions. The description in this section is not relevant to the research and has been deleted.

Comment # 9: R 217-220 please explain the context for 2004-2019) now explanation is very simple (figure 2-4 didn't explain the variation of the NPP)

Response: We have added a description to figure 2-4 to better demonstrate the changing trend of NPP in Hetao Irrigation District, Inner Mongolia from 2001 to 2021 in lines 226-233 and 241-255 in the revised manuscript.

Comment # 10: For figures 2-4, change the direction of the years on the OX axis to make it easier to understand

Response: We have made modifications to the OX axis direction of figures 2-4 to make it easier to understand.

Comment # 11: Subchapter 3.1. significant improvement must be completed as well as 3.2, Subchapter 3.2 is very general and does not explain the spatio-temporal variability of NPP

Response: Thank you for your constructive suggestions. We have made modifications to the Subchapter 3.1 and 3.2 in the revised manuscript. Section 3.1 primarily analyzes the temporal variation patterns of NPP in the Hetao Irrigation District of Inner Mongolia at different scales, including yearly, every 8 days, monthly changes over the years. We have conducted a more in-depth analysis in Section 3.1.

  In Section 3.2, the focus shifts to examining the spatial variability of NPP in the same region, specifically exploring the spatial distribution on a yearly and monthly. We have expanded our explanation of the spatiotemporal variability of NPP. This includes a detailed description of how the spatial distribution of NPP in the Hetao Irrigation District of Inner Mongolia changes over time. We analyze the spatial distribution of NPP on an annual and monthly basis, and discuss how these spatial patterns evolve over time. Additionally, we explain the geographical, climatic, and anthropogenic factors that may contribute to these spatiotemporal variabilities, and explore their implications for the irrigation area ecosystem.

Comment # 12: R338-340 the information is repeated (they are also in the methodology section)

Response: Thanks for your constructive suggestions. We have removed this duplicate information and made it only visible in the methodology section.

Comment # 13: The entire Results section needs to be significantly improved and completed. Currently, the text only explains the figures.

Response: Thank you for your constructive suggestions. We have made modifications to the entire Results and Discussion section, providing a more in-depth analysis of the graph and a more in-depth discussion of the results of this study based on existing research.

Comment # 14: Add a discussion section where you can compare your results with similar studies. Show the limits of the study and future research directions.

Response: Thank you for your constructive suggestions. The third part of our study is the Results and Discussion section. We have revised the Discussion section to clearly compare our research results with existing studies and to highlight the limitations of existing research, thereby emphasizing the novelty of our study.

Comment # 15: Correlate the results and conclusions section with the purpose and objectives that you will go through in the introduction

Response: Thank you for your constructive suggestions. We have made modifications to the Results and Conclusion sections to better align with the purpose in the introduction.

Comment # 16: Currently the conclusions are not very clear - 399-402 ("non-significant increase" and "decreasing trend in the future NPP changes")

Response: Thank you for your constructive suggestions. We have made modifications to the conclusion for clearer expression and better understanding in lines 432-437 in the revised manuscript.

Comment # 17: The last lines should be relevant to the study but not to the conclusions "analyze the driving factors influencing NPP changes and elucidate the response mechanisms of NPP"

Response: Thank you for your constructive suggestions. We have made modifications to the conclusion in lines 437-443 in the revised manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents a study that evaluates the changes in Net Primary Productivity (NPP) from 2001 to 2021 using the MOD17A3/NPP product. To assess the spatiotemporal distribution patterns of NPP, the Theil-Sen Median trend, Mann-Kendall significance, and Hurst index were employed. The content is interesting, but there are some points of concern as follows:

1. Introduction

There are numerous previous studies evaluating the changes in NPP in Inner Mongolia (e.g. Mu et al., 2013: DOI:10.5846/stxb201205030638). Please clarify the issues with these studies and elucidate the novelty of this research.

2. Data and research methods

You know the Theil-Sen median trend analysis can be sensitive to tied data, where multiple data points have the same value. And it is less efficient than parametric methods. Some studies expressed spatio-temporal changes of the NPP of Inner Mongolia vegetation during using the Carnegie-Ames-Stanford Approach (CASA) model. 

Why did you apply the Theil-Sen median trend analysis?

3. Results and analysis

In Figure 1, a land use map is presented, but was there no change over the 21-year period? Have you evaluated the impact of changes in land use on NPP changes?

Is it possible to clarify the differences in estimation results compared to using existing models?

Author Response

General Comments

This paper presents a study that evaluates the changes in Net Primary Productivity (NPP) from 2001 to 2021 using the MOD17A3/NPP product. To assess the spatiotemporal distribution patterns of NPP, the Theil-Sen Median trend, Mann-Kendall significance, and Hurst index were employed. The content is interesting, but there are some points of concern as follows:

Response:

We appreciate that you are interested in our research work. We took these comments seriously and responded to all comments carefully. Details of all changes we made are shown below.

Comment # 1: Introduction

There are numerous previous studies evaluating the changes in NPP in Inner Mongolia (e.g. Mu et al., 2013: DOI:10.5846/stxb201205030638). Please clarify the issues with these studies and elucidate the novelty of this research.

Response: Thank you for your constructive suggestions.

We have made modifications in the introduction section to clarify the issues with these studies and elucidate the novelty of this research in lines 102–132 in the revised manuscript.

Comment # 2: Data and research methods

You know the Theil-Sen median trend analysis can be sensitive to tied data, where multiple data points have the same value. And it is less efficient than parametric methods. Some studies expressed spatiotemporal changes of the NPP of Inner Mongolia vegetation during using the CASA model. Why did you apply the Theil-Sen median trend analysis?

Response: This study utilizes MOD17A3H NPP data (https://developers.google.com/earth-engine/datasets/catalog/?filter=MODIS%2F006%2FMOD17A3HGF) to analyze the spatiotemporal changes in NPP in the Hetao Irrigation District of Inner Mongolia from 2001 to 2021. The MODIS17A3H NPP product employs a process-based Biome-BGC ecological model to estimate NPP. Compared to other models, the Biome-BGC process model utilizes more parameters and more precise estimation methods, thereby improving the accuracy of NPP estimation. MOD17A3/NPP data, as one of the most widely used data sources for global and regional NPP and carbon cycling studies, has the widest spatial coverage, longest time span, clearer physiological and ecological mechanisms, and more accurate estimation results among current global land NPP products. In recent years, with the rapid development of remote sensing technology, the analysis of spatiotemporal variations in regional NPP using MOD17A3/NPP data has become a focus of research for scholars in relevant fields.

Currently, methods for estimating NPP based on remote sensing data combined with models mainly include the CASA model and the Biome-BGC model. The CASA model is a light use efficiency model used to estimate regional NPP. The model is driven by remote sensing data, temperature, precipitation, solar radiation, vegetation type, soil type, and other data. NPP in this model is determined by two variables: the absorption of photosynthetically active radiation by vegetation and the light use efficiency [1-3]. The Biome-BGC model, on the other hand, is a bio-geophysical chemical model that uses meteorological data, study area parameters, and ecological data as the main factors. It analyzes plant ecological and physiological processes in detail, particularly simulating responses to climate change [4-6]. Among many models, the Biome-BGC model is characterized by strong mechanistic principles and provides detailed and accurate descriptions of key ecological processes. It is widely used globally and has a broader time scale, making it better suited for in-depth analysis of spatiotemporal variations in NPP. Therefore, our study utilizes the MOD17A3H NPP data, which combines the Biome-BGC model with a light use efficiency model, to analyze the spatiotemporal distribution of NPP in the Hetao Irrigation District of Inner Mongolia over the years. The MOD17A3H NPP data are widely used in current research [7-9].

Our study utilizes Theil-Sen median trend analysis to analyze the monthly and annual trends in the Hetao Irrigation District of Inner Mongolia from 2001 to 2021, revealing the changing patterns over the past 21 years. This method is also widely used in research analyzing spatiotemporal characteristics of NPP over the years [10-12]. The above is my answer to this question. If my explanation is not clear enough, please contact me again.

References:

1. Liu, Z.; Hu, M.; Hu, Y.; Wang, G. Estimation of net primary productivity of forests by modified casa models and remotely sensed data. International Journal of Remote Sensing. 2018, 39, 1092-1116.
2. Bao, G.;Bao, Y.;Qin, Z.; Xin, X.; Bao, Y.; Bayarsaikan, S.; Zhou, Y.; Chuntai, B. Modeling net primary productivity of terrestrial ecosystems in the semi-arid climate of the Mongolian Plateau using LSWI-based CASA ecosystem model. International Journal of Applied Earth Observations & Geoinformation. 2016, 46:84-93.
3. Tang, C.; Fu, X.; Jiang, D.; Fu, J.; Zhang, X.; Zhou, S. Simulating spatiotemporal dynamics of sichuan grassland net primary productivity using the casa model and in situ observations. Scientific World Journal. 2014, 1-12.
4. Sun, Q.; Li, B.; Zhang, T.; Yuan, Y.; Gao, X.; Ge, J.; Li, F.; Zhang, Z. An improved Biome-BGC model for estimating net primary productivity of alpine meadow on the Qinghai-Tibet Plateau. Ecological Modelling. 2017, 350:55-68.
5. Hidy, D.; Barcza, Z.; Haszpra, L.; Churkina, G.; Nagy, Z.; Development of the biome-bgc model for simulation of managed herbaceous ecosystems. Ecological Modelling.2015, 226, 99-119.
6. Han, Q.; Luo, G.; Li, C.; Xu, W. Q. Modeling the grazing effect on dry grassland carbon cycling with biome-bgc model. Ecological Complexity,2014,17, 149-157.
7. Yuan, X.; Guo, B.; Lu, M. The Responses of Vegetation NPP Dynamics to the Influences of Climate-Human Factors on Qinghai-Tibet Plateau from 2000 to 2020. Remote sensing, 2023,15,2419.
8. Yang, H.; Zhong, X.; Deng, S.; Xu, H. Assessment of the impact of LUCC on NPP and its influencing factors in the Yangtze River basin, China. Catena. 2021, 206, 105542.
9. Gulbeyaz, O.; Bond-Lamberty, B.; Akyurek, Z.; West, T.O. A new approach to evaluate the MODIS annual NPP product (MOD17A3) using forest field data from Turkey. Int. J. Remote. Sens. 2018, 39, 2560–2578.
10. Chen, Y.; Wang, J.; Xiong, N.; Sun, L.; Xu, J. Impacts of Land Use Changes on Net Primary Productivity in Urban Agglomerations under Multi-Scenarios Simulation. Remote sensing. 2022,14,1755.
11. Hao, X.; Wang, X.; Ma, J.; Chen, Y.; Luo, S. Spatiotemporal Characteristic Prediction and Driving Factor Analysis of Vegetation Net Primary Productivity in Central China Covering the Period of 2001-2019. Land, 2024,12,2122.
12. Ba, W.; Qiu, H.; Cao, Y.; Gong, A.; Li, M. Spatiotemporal Characteristics Prediction and Driving Factors Analysis of NPP in Shanxi Province Covering the Period 2001–2020. Sustainability, 2023, 15, 12070.

Comment # 3: Results and analysis

In Figure 1, a land use map is presented, but was there no change over the 21-year period? Have you evaluated the impact of changes in land use on NPP changes?

 Is it possible to clarify the differences in estimation results compared to using existing models?

Response:

This study did not conduct a quantitative analysis of land use and NPP. Instead, it only utilized the land use map of the Hetao Irrigation District of Inner Mongolia in 2021 to illustrate the land distribution in the study area. It is noted in the literature that while there may have been changes in land distribution in the area over the past twenty years, overall changes have been relatively minor [1-3]. The main focus of this study is to analyze the spatiotemporal distribution of NPP in the Hetao Irrigation District of Inner Mongolia from 2001 to 2021 at different temporal scales. The Theil-Sen median trend analysis was used to reveal the trends in monthly and annual changes over the past 21 years. Additionally, the Hurst index was utilized to forecast future changes in NPP in the study area. Future research may focus on analyzing driving factors such as meteorological factors and land use that affect the NPP of Hetao Irrigation District. The above is my answer to this question. If my explanation is not clear enough, please contact me again.

References:

1. Zhang, Y.; Luo, Y.; Liu, J.; Zhuang, D. Changes in land use in the Hetao Irrigation District of Inner Mongolia and their landscape ecological effects. Resources Science, 2005, 141-146.
2. Li, X. Study on the Impact of Land Use Changes in the Hetao Irrigation District of Inner Mongolia on Irrigation Hydrological Processes. Northwest A&F University, 2017.
3. Yang, Y. Analysis and Implementation of Land Use Changes in the Hetao Irrigation District Based on TM Remote Sensing Images. Northwest A&F University, 2017.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript was revised

Reviewer 2 Report

Comments and Suggestions for Authors

The authors added some elements to enrich manuscript and I think this paper can now be accepted for publication.