Spatiotemporal Variation of Net Primary Productivity and Its Response to Climate Change and Human Activities in the Yangtze River Delta, China
Round 1
Reviewer 1 Report
The introduction gives some interesting ideas but it fails to connect to connect clearly to the research aims of the paper. Also, the paper would benefit from discussing how the findings relate to the broader aspects of NPP and applications outside the study area. The paper might also be shorter with more concise explanations. Finally, in figure one it is not explicit what the land use 'construction' means.
Author Response
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Reviewer 2 Report
In this study Li et al. analyze the spatiotemporal dynamics of NPP in a Yangtze River delta, China, in relation to environmental parameters and land use for a 20-year period. The topic is of great importance, as highlighting NPP trends and responses to environmental parameters can offer a good estimation about future trends under different climate/land use change scenarios. The authors use as basis a well known NPP product from Modis and climatic/meteorological data from several databases. They examine the trend of NPP for the 20-year period, as well as they try to assess some future projections with the use of several sophisticated statistical methods. The paper is quite well structured. The databases and methodologies used are presented very well and can offer a good summary of the methodology for relevant studies. The results are clear and focused. Weaknesses and uncertainties that arise from the fact that some critical environmental factors are not taken into account are also highlighted.
However, I have some major concerns:
1. The Modis NPP is actually a modeled product. One of the inputs for the NPP estimation is temperature, that is also used as an independent parameter from the authors to relate it to the NPP differentiations. This is a part that the authors should highlight and put some effort in the discussion.
2. Some detail should be added to the figure’s captions. Figures should be more “self-explanatory”, if possible.
3. When Pearson correlation coefficient is used, p values should be estimated and added as well. This could be a good indicator for the significance of the relationships.
Some more comments can be found in the attached file.
I think that the paper can be published in the Applied Sciences journal, after the implication of the proposed adjustments.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
I appreciate the opportunity to review the manuscript entitled “Spatiotemporal variation of Net Primary Productivity and response to climate change and human activities in the Yangtze River Delta, China”. Herein the authors present an assessment of the effects of environmental variables and human activities on Net Primary Productivity (NPP) and the future change trend of NPP in the region. The article provides scientific knowledge linking statistical analyses and NPP data for the 2000-2019 time series. Statistical analysis among studied variables detected that NPP was generally on an increasing trend in the research region. This study results interesting because is crucial to anticipate changes of vegetation productivity. I have minor concerns as follows.
My overall critique does not include the grammatical errors, so please don't consider my review as such.
Abstract.
Line 10-12. This sentence is too long, please rewrite.
Introduction.
The influence of several drivers on vegetation dynamics along elevation gradients have already been analyzed with several methods in the world. For example, there is recent and allusive literature on the subject (see https://doi.org/10.1016/j.scitotenv.2021.145286, and others related). These literature references will be useful to provide structure for the Discussion section.
On the other hand, there is no hypothesis explicitly presented. I urge the authors to transform the objectives stated into full on hypotheses by suggesting a directionality to the relationships being investigated.
Methods
I thought, coordinates mentioned in L 103 should be removed because they are not intuitive for the reader. Instead, I think that map in figure 1 is more suitable.
Add climograph figure as usual in modern literature (e.g. Box and whiskers plot to illustrate distribution of monthly precipitation and temperature values over the length of the record).
Results
Figure 1 is of poor quality. The text must be edited to ensure the proper font resolutions.
Discussion.
As suggested above, it would be beneficial to set more related references in the Introduction and use them as a guidance for Discussion.
Line 397-439: It would be worth to present more evidence for other seasonal ecosystems worldwide, which should bring more attention to your paper (see https://doi.org/10.1016/j.scitotenv.2021.145286)
Line 511. What are other limitations to this paper and what might make the results inaccurate (which assumptions might be wrong?) How certain are you? Despite this comment, I do think this is a valuable paper. For instance, discuss about the short temporal period to test variables dynamics and NPP data. This low period might represent misleading trends.
Conclusions
Line 535. The authors conclude “…urban expansion and population increase resulted in the decrease of NPP”. I think it is obvious.
In summary, my decision based upon above comments is that the current manuscript could be considered for publication only if a minor revision addressing every single point indicated is satisfactorily answered.
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
Paper entitled “Spatiotemporal variation of Net Primary Productivity and response to climate change and human activities in the Yangtze River Delta, China” meets the necessary standards for publication in this journal.
Please check the entire manuscript carefully for eventual typographical errors.
Attention when writing references. They are not unitary.
Final Conclusion: The paper meets the necessary standards for publication.
Author Response
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Author Response File: Author Response.docx
Reviewer 5 Report
Li et al. evaluated the spatiotemporal variation, trends of NPP, and various factors that influence NPP in the Yangtze River Delta region from 2000 to 2019. With various statistical methods, the author suggested that the future trend of NPP is dominated by an anti-persistence trend in the study area; annual precipitation was the most significant positive driver for NPP. There are two-factor enhanced interactions between different drivers. The topic of the paper is appropriate for the special issue "Advances in Geospatial Techniques on Ecosystem Monitoring,” but the paper is not well prepared. I see little novelty value in the results. The grammar/English needs some work. Therefore, the manuscript cannot be published without substantial additional work and I suggest rejecting the manuscript in its current form.
Major concerns:
(1) Many papers have investigated the change in the carbon cycle in the Yangtze River Delta region; what ''s new in this paper?
(2) The grammar/English needs more work. There are many errors and awkward sentences. Many sentences aren’t unable to articulate your thoughts.
(3) A more nuanced discussion is needed. The authors didn’t explain some results and ignored some key factors.
minor points:
data selection: Meteorological variables mainly include monthly average temperature, total precipitation, and total sunshine hours. It seems like using annual average data of climate data after interpolating. You should include the seasonal pattern as this area has an important seasonal pattern of precipitation. Solar radiation may be a better variable than total sunshine hours.
Correlation Analysis should think about the partial correlation instead of the Pearson correlation coefficient.
Specific points:
Title: Spatiotemporal variation of Net Primary Productivity and its response to climate change and human activities in the Yangtze River Delta, China.
Line 13: future trends.
Line 14: Theil-Sen Median. Don’t coin new terms; use the commonly used terms, such as Sen's Slope/Theil–Sen estimator.
Line 17: various drivers change to environmental factors.
Line 21: delete (increasing).
Line 22: rewrite this sentence.
Line 32: redundant sentence, rewrite it.
Line 35: “their own” is redundant.
Line 39 “also” is redundant.
Line 43: delete “therefore.”
Line 47: delete “It is now generally accepted that”
Line 54: conducted on understanding…
Line 64: there are more approaches to assess factors that impact NPP, such as land surface modeling.
Line 89: what do you mean by providing data support? Please elaborate.
Line 93: future trends.
Line 154: the natural breakpoint method needs to be explained in detail.
Line 166: This is not a commonly used term.
Line 245: Use several simple sentences instead of a long sentence, it is hard to follow.
Line 263: Why do you use a piecewise regression model, actually Mann-Kendall also can detect changing points.
Line 263: Why is 2009 the turning point? I expected to see more analysis and discussion.
Line 316: I didn’t see the Risk detector explained like this, in Wang, Jin-Feng, and Yi Hu. "Environmental health risk detection with GeogDetector." Environmental Modelling & Software 33 (2012): 114-115. Give more detail and with citation.
Line 320: The slope extracted from elevation can’t explain there was a similar change pattern between elevation and slope classification and NPP.
Line 333: awkward sentence.
Line 336: what is the point of the average Pearson correlation coefficient across grid cells area?
Line 352: population density?
Line 363: what is the change in the land cover area?
Line 403-406: awkward sentence; rewrite it.
Line 460: Population growth and urbanization impact the impervious surface. You need to analyze and discuss how the construction land area in relation to population and its impacts on NPP.
Comments for author File: Comments.pdf
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 5 Report
The manuscript is greatly improved relative to the first version I read. I think it is in a good shape now. I recommend it for publication.
Author Response
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