The Impact of Global Warming on the Winter Wheat Production of China

Round 1

Reviewer 1 Report

There some minor suggestions about English wording. Some explanation should be given on temperature changes given in Table 2 compared to the trends given at lines 59-60. It seems the figures in Table 2 might be 10 year and not one-year trends. Needs explaining.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

We greatly appreciate your kind comments and suggestions, and these have been helpful to improve our manuscript. Please see our point-by-point response in the attachment. Thank  you.

Best Regards,

Yu Zhang

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors

Thanks for a very clearly written paper! My comments below are grouped as "Generic" ans "Specific", which refer to "Specific lines", including language editing. 

Generic

A. The paper very often uses the past tense when the present is required. I have mostly ignored this, but you may wish to have the paper checked for the use of tenses. There are, however, some cases where I have suggested to change this, for instance (line 100) where I read “The
details of the dataset were listed in Table 1.” This should be “The details of the dataset are listed in Table 1.” or, possibly “The details of the dataset have been listed in Table 1.”

B. The paper builds on GDD, which is a standard yet unsophisticated approach. DD methods are “phenomenological” (i.e. descriptive) and basically lack any physiological and physical basis. There are not “models” (in the sense of “process based models” but a “trick” based on the fact that daily sums (of temperatures) increase over time.  This also applies to the “base temperature” which is a conventional reference. I think your figure 3 is, in itself, an excellent illustration of the fact that DD-based approaches are not very realistic. You mention this on line 240, but photoperiod is just one of the possible factors. Water stress is another, important one. Of course, heat (as estimated by temperature) is an important factor in crop development, but the effect is more complex than linear DD accumulation. You must also be aware that formulations like your title 3.5 is, strictly, incorrect. This is because HDD is a human invention and not an eco-physiological factor. Heat affects yield and it’s components, but HDD is just a simple way to assess heat impact on crop growth and development. 

Also note that when you say “However, using the crop growth models to estimate the effect of climate change on crop production is an indirect method” you are suggesting that DD methods are “direct methods”, which is very wrong… as I have mentioned. You should also remember that crop growth simulation models almost all use DD methods to estimate phenology, i.e. the “simulation models” do basically the same as what you have done. Therefore, saying that your approach is “better” is a bit of an exaggeration. 

The introduction should mention that GDD/HDD methods are largely conventional and that there are other methods with a sounder and more “scientific” eco-physiological and physical basis, for instance because they take into account the effect of photoperiod, vernalization, water and cold stress on crop development.  It would be interesting if you could redo this work with one of the more modern phenology models.

C. The paper also decides to completely ignore rainfall, sunshine and irrigation volumes. See my comments to lines 83 and 101 (Table 1). Table 1 should mention elevation, average rainfall, average sunshine and average volumes of irrigation for each of the stations, for the duration of the growing cycle (as opposed to calendar year from January to December).

D. The paper quotes only old references (up to 2015, with one paper published in 2017). I assume this is also why the authors quote an outdated wheat production figure on line 43. 

Specific

Explanation:

33, 47: Good morning -> Hello

means that on lines 33 and 47 I suggest that Good morning should become Hello

5, 12: information agriculture → information in agriculture
Comment: this could also be “information for agriculture”. Refer to the official English name of the institutions and correct

20: which planted more → which were planted during more

27: length of growth periods → periods

32-34: The reason for this phenomenon is HDD between anthesis and maturity was not changed significantly in the Northern Winter Wheat Region of China, which could not lead to the yield decline. 
Comment: this is not clear. Drop the sentence.

34: cause → factor
Comment: you can also say “determinant”

35: and heat stress event → the frequency of heat stresses

37: for food security policies in either China or the world. → for the implementation of food security policies.

41: Wheat is the third largest crop → Wheat is the third most produced crop

42: source of carbohydrates → staple
Comment: there is much more to wheat than starch!

43: 200 million → 216 million 
Comment: according to FAOSTAT in 2019

46: must → should
Comment: as you are aware, wheat yields have been stagnating in major producers for a number of years (at least 10) , which is why the crop was overtaken by Maize.  Search the web for “wheat yield stagnation” and mention the fact, as well as it’s causes. This is an essential piece of information missing from your paper.

50-51: researches → research

58: trace gases → atmospheric pollution
Comment: the use of “trace gases” is ambiguous, as the wording normally means Argon, Krypton, Xenon, Neon etc. and not specifically such gases as ozone or nitrous oxides. 

59-60: 0.13 °C per decade since 1950 and is projected to increase 0.2 °C per decade
Comment: use one or two decimals, not two (0.13) and then 1 (0.2). If 0.2 is 0.20, say 0.20!

61: Associating → Together 
Comment: or “Associated”

61: the heat stress event becomes more common → heat stress becomes more common

67: evidences → evidence

83: daily minimum and maximum temperature
Comment: (Also refer to “generic comment C”). I am very surprised that you have no rain and no sunshine. The variable (factor) driving growth is sunshine, and the use of sunshine is “paid for” with water. You can assume that Tmax is a proxy for sunshine, but what about rainfall. Is the crop 100% irrigated? What is average rainfall in the area under study? Table 1 should mention additional reference values for the listed stations.

84: were maintained → are operated

97: wheat planting area → wheat cultivation area

98: yield → production
Comment: I guess you mean “production” or “output” rather than “yield”

100: were → are
Comment: see generic comment A. The data “are” listed. I can see them now, present tense. 

101: As mentioned above, the table should also provide elevation, average rainfall, average sunshine and average volume of irrigation

118: reality
Comment: I assume you are aware that we are talking of “practice” more than “reality”, as the GDD “model” is a very elementary and unrealistic one. Refer to my generic comment B.

146-147: The spatial patterns of average temperatures in the winter wheat growing seasons
experienced the similar historical trends → Average temperatures follow similar patterns in the  stations of the winter wheat growing areas. 
Comment: statial pattern is misleading, as you just have point observations.

148: temperature with time → temperature
Comment: drop “with time”

151-152: the decreasing trend of average temperature was not found → no decreasing trend was found 

172: be varied → vary

173: kept → remained
Comment: or “stayed”

179, 180, 181: enhanced → changed by

240: photoperiodic response during this phase
Comment: yes, and you could also mention this as one of the many limitations of the DD approach

249: devoted to → available for

262: At → In

269: 406.3 kg ha-1
Comment: you really can asses this with a precision of 0.02% (0.1 kg in 406.3 kg) ? 

287: was agreement → was in agreement
Comment: or “agrees”

289: yet → although

292: decline → decrease
Comment: or “reduce”

302: model is a useful tool → models are useful tools

309: planted more than 15 years → planted during more than 15 years

315: to be risen → to rise

316: decades → decade

318: produce the negative → produce negative

333: 
Comment: I have not checked the references, but nevertheless noted that there is only one paper more recent than 2015 (published 2017). 

Author Response

Dear Reviewer,

We greatly appreciate your kind comments and suggestions, and these have been helpful to improve our manuscript. Please see our point-by-point response in the attachment.

Thank  you!

Best Regards,

Yu Zhang

Author Response File: Author Response.docx