Responses of Winter Wheat Yield to Drought in the North China Plain: Spatial–Temporal Patterns and Climatic Drivers

Round 1

Reviewer 1 Report

This is an interesting paper and well written.

However, the MS is not ready to be published due to the following reasons:

1. The literature for the effect of spatial-temporal patterns and climatic drivers on crop yield were not well introduced.
2. The EPIC model is critical tool for this study. However, the model performance is only evaluated by grain yield. The phonological stages from model were not fully explored.
3. The statistical model is also play an important role in this study. However, the colinearity is not discussed especially for PDA and table 3.
4. The effect of spatial-temporal patterns and climatic drivers on crop yield was not well discussed.

Author Response

Response to Reviewer 1 Comments

Thank you very much for your valuable comments and suggestions, which are very helpful to improve this paper. According to your comments, the manuscript was revised carefully and the detailed responses are listed as follows.

Point 1: The literature for the effect of spatial-temporal patterns and climatic drivers on crop yield were not well introduced. 


Response 1: We appreciate and agree with this feedback that the literature for the effect of spatial-temporal patterns and climatic drivers on crop yield were not well introduced. Based on this feedback, in the revised paper we first summarized the research progress of crop yield response to drought (Line63-Line83). At the same time, the research progress about the impact of climate factors on crop yields also has been added (Line84-Line97). Then we summarized the limitations of previous related and talk about the importance to carry out this research in the North China Plain (Line98-Line117).

Point 2: The EPIC model is critical tool for this study. However, the model performance is only evaluated by grain yield. The phonological stages from model were not fully explored.

Response 2: We thank for the reviewer for these comments. It is a truth that crop models were usually calibrated based on crop yields and phenological stages in the field scale research. However, our study was carried out in the North China Plain (NCP), it is difficult to obtain the crop growth period on each simulation station in a large spatial scale, and hence the model performance is only evaluated by grain yield and the phenological stages from model were not fully explored. Though some studies also only calibrated crop yields due to the data limitations in a large spatial scale [1,2], this is still a limitation of our study and in the follow-up research, we will analysis the response patterns and climatic drivers of winter wheat to drought in detail based on the field experiment.

Point 3: The statistical model is also play an important role in this study. However, the colinearity is not discussed especially for PDA and table 3.

Response 3: Thank you for your comment，according to you advice，in the revised manuscripts, we have added a further description of the predictive discriminant analysis (PDA) method (Line267-Line271). Predictive discriminant analysis (PDA) is commonly used to explain the value of a dependent categorical variable based on its relationship to one or more predictors. Given a set of independent variables, PDA attempts to identify linear combinations of those variables that best separate the groups of cases of the dependent variable. We admit that the PDA method cannot eliminate the collinearity between independent variables very well. However, our research pays more attention to which climactic factors contribute more to the response of winter wheat to drought. If we consider the collinearity, we may not be able to distinguish the different contribution of the maximum temperature, minimum temperature and the mean temperature. The PDA method gives the relative importance of each climatic factors by the discriminant function (Table 3, Line451). Hence, according to the previous studies [3,4], the PDA method was chosen to studies the driving factors of winter wheat yield to drought in our study.

Point 4: The effect of spatial-temporal patterns and climatic drivers on crop yield was not well discussed.

Response 4: We thank the reviewer for these comments. In order to be understood easily, we divided the discussion part into three subsections in the revised paper. And in the second subsection, according to this comments, we have strengthened the discussion about the effect of spatial-temporal patterns and climatic drivers on crop yield.

• In Line 504~Line 510, we supplemented the prior studies about the climatic drivers leading to the different crop yield responses to drought, and gave the general explanation.
• In our study, we found that temperature plays a more important role in influencing the different spatial response patterns of winter wheat yields to drought in the NCP. So in Line 515-522, we summarized the previous studies which also emphasized the importance of temperature in influencing crop yields.
• In Line 522-527, we explained why we believe that global warming enhances the role of temperature in winter wheat yield responses to drought.
• In Line 529-532, we added our opinion that how temperature rise affects crop yield responses to drought requires further research and analysis against the backdrop of global warming.

 

Reference

1. Kamali, B.; Abbaspour, K.C.; Wehrli, B.; Yang, H. Drought vulnerability assessment of maize in Sub-Saharan Africa: Insights from physical and social perspectives. Global and Planetary Change 2018, 162, 266–274, doi:10.1016/j.gloplacha.2018.01.011.
2. Qiao, J.; Yu, D.; Liu, Y. Quantifying the impacts of climatic trend and fluctuation on crop yields in northern China. Environmental monitoring and assessment 2017, 189, 532, doi:10.1007/s10661-017-6256-0.
3. Peña-Gallardo, M.; Vicente-Serrano, S.M.; Quiring, S.; Svoboda, M.; Hannaford, J.; Tomas-Burguera, M.; Martín-Hernández, N.; Domínguez-Castro, F.; El Kenawy, A. Response of crop yield to different time-scales of drought in the United States: Spatio-temporal patterns and climatic and environmental drivers. Agric. For. Meteorol. 2019, 264, 40–55, doi:10.1016/j.agrformet.2018.09.019.
4. Vicente-Serrano, S.M.; Camarero, J.J.; Azorin-Molina, C. Diverse responses of forest growth to drought time-scales in the Northern Hemisphere. Glob. Ecol. Biogeogr. 2014, 23, 1019–1030, doi:10.1111/geb.12183.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Manuscript entitled: „Responses of winter wheat yield to drought in the North China Plain: Spatial-temporal patterns and climatic drivers” presents interesting topic on drought effect on wheat yield.

The topic is very important in current time of climate change and most frequent droughts in different world regions.

Introduction and methodology in the study is well described. In material and methods particularly useful is Fig. 2 which presents “Methodological frame work of this study” and allows to better understand all processes in the study. Moreover, supplementary materials provide additional useful figures and tables which clarify the methodology of the study.

Manuscript in general is well organized and well prepared, however contains some drawbacks. Below are detailed comments for the manuscript:

1) The caption for Fig. S4 is following: “Same as Supplementary Fig. 1, but for summer” but Fig. S1 presents maps. It should be probably: “Same as Supplementary Fig. S3, but for summer”? Similar error is in case of Fig. S5 and Fig. S6.

2) Correlations between grain yield versus drought level (SPEI) are calculated across years. The period was quite long, i.e. from 1980 to 2013. Most probably in this period cultivars of winter wheat were different. Yield potential of new bred cultivars is usually higher. How in the study such effect was removed? Moreover, in such long period other factors are changing, e.g. progress in pesticides or other agronomic technology is observed. Was in the study included effect of such changes?

3) The description of the tables and the figures should be clear enough without reading all the text of the manuscript. The figures and the tables should be self-explanatory. In the manuscript this rule is not fulfilled for example in case of Fig. 6. It is not clear what period was used for the analyses presented in Fig. 6a and 6b. It should be clearly stated.

4) It would be good if information about growth crop stages in different parts of NCP will be added. For such cereals, including winter wheat, most important crop stages before flowering, flowering and after flowering. Crucial growth stages are different in different regions. Maybe mean correlations should be calculated by growth stage not by month?

5) It would be more clear if full description “The time-scales of the SPEI” or “time-scale drought” instead of short “time-scale” was used in different parts of the manuscript, including figures.

6) The study focuses on effect of drought. The excess of water was not observed in some of the regions? It would be good if different patterns of correlations between SPEI in different regions (north and south) was better explained. The genotypes of winter wheat cropped in different regions are similar or quite different? It is known that genotype x environment interaction has strong effect on grain yield.

Author Response

Response to Reviewer 2 Comments

Thank you very much for your valuable comments and suggestions, which are very helpful to improve this paper. According to your comments, the manuscript was revised carefully and the detailed responses are listed as follows.

Point 1: The caption for Fig. S4 is following: “Same as Supplementary Fig. 1, but for summer” but Fig. S1 presents maps. It should be probably: “Same as Supplementary Fig. S3, but for summer”? Similar error is in case of Fig. S5 and Fig. S6. 


Response 1: Thank you, we have modified it in the Supplementary Materials.

• In Supplementary Materials, Line 31, we changed “Same as Supplementary Fig. 1, but for summer” to “Same as Supplementary Fig. 3, but for summer”.
• In Supplementary Materials, Line 33, we changed “Same as Supplementary Fig. 1, but for autumn” to “Same as Supplementary Fig. 3, but for autumn”.
• In Supplementary Materials, Line 35, we changed “Same as Supplementary Fig. 1, but for Winter” to “Same as Supplementary Fig. 3, but for Winter”.

Point 2: Correlations between grain yield versus drought level (SPEI) are calculated across years. The period was quite long, i.e. from 1980 to 2013. Most probably in this period cultivars of winter wheat were different. Yield potential of new bred cultivars is usually higher. How in the study such effect was removed? Moreover, in such long period other factors are changing, e.g. progress in pesticides or other agronomic technology is observed. Was in the study included effect of such changes?

Response 2: Thank you for your careful comments. (1) Indeed, the cultivars of winter wheat may change from 1980 to 2013. In our research, by verifying the crop model, we have obtained crop parameters that can represent the average condition of winter wheat varieties for many years. This set of crop parameters remains unchanged throughout the simulation process, so that we can eliminate the impact of variety differences over the years. (2) We admitted that in such long period pesticides or other agronomic technologies are improving are changing. However, due to the limitation of data availability, our research assumes that the above factors are constant, and did not consider the effect of such changes.

Point 3: The description of the tables and the figures should be clear enough without reading all the text of the manuscript. The figures and the tables should be self-explanatory. In the manuscript this rule is not fulfilled for example in case of Fig. 6. It is not clear what period was used for the analyses presented in Fig. 6a and 6b. It should be clearly stated.

Response 3: Thank you for your suggestion, we have modified the description of some tables and figures in the revised manuscripts.

Point 4: It would be good if information about growth crop stages in different parts of NCP will be added. For such cereals, including winter wheat, most important crop stages before flowering, flowering and after flowering. Crucial growth stages are different in different regions. Maybe mean correlations should be calculated by growth stage not by month?

Response 4: This is a suggestion with reference value. However, the minimum time resolution of SPEI is one month. The different growth stages of winter wheat may span different months or the length of the growth stages is less than 1 month. It is difficult to describe the drought characteristics of a certain growth period by the SPEI, so we did not calculate the correlations by growth stages.

Point 5: It would be more clear if full description “The time-scales of the SPEI” or “time-scale drought” instead of short “time-scale” was used in different parts of the manuscript, including figures.

Response 5: Thank you, we have given the full description of the “time-scale” in the revised manuscripts (including figures) according to the comment.

Point 6: The study focuses on effect of drought. The excess of water was not observed in some of the regions? It would be good if different patterns of correlations between SPEI in different regions (north and south) was better explained. The genotypes of winter wheat cropped in different regions are similar or quite different? It is known that genotype x environment interaction has strong effect on grain yield.

Response 6: Thank you for your comments.

(1) The excess of water was not observed in some of the regions?

This is a good suggestion. According to your suggestion, we counted the number of winter wheat growing season with different moist degree at each station (Figure 1) Based on the SPEI. And we found that 1) Severe moist and extreme moist did not occur frequently at each station, indicating that the main factor limiting wheat production in the NCP is not excessive moisture; 2) The stations where extreme moist occurred are mainly distributed in the southern part of the NCP, it indicates that excessive precipitation in some year may adversely affect wheat production in the south part of the NCP. We also used this finding in the revised script to explain why the correlation between winter wheat yield and SPEI in the southern region is not significant (Line498-Line501).

Figure 1. the count of winter wheat growing season with different moist degree at each station from 1980 to 2013

(2) The genotypes of winter wheat cropped in different regions are similar or quite different?

In our research, we verified the crop variety parameters of winter wheat at 16 agrometeorological stations. The wheat genotypes of these 16 agrometeorological stations are different. For other stations, we assumed that stations close to each other would plant the same varieties of winter wheat, so we used the winter wheat variety parameters of the station closest to it. We admitted this is one limitation of our study though some studies have adopted the similar strategies [1,2], and we have discussed it in the discussion part of the revised manuscripts [Line547-Line550].

Reference

1. Yue, Y.; Li, J.; Ye, X.; Wang, Z.; Zhu, A.-X.; Wang, J.-a. An EPIC model-based vulnerability assessment of wheat subject to drought. Nat. Hazards 2015, 78, 1629–1652, doi:10.1007/s11069-015-1793-8.
2. Qiao, J.; Yu, D.; Liu, Y. Quantifying the impacts of climatic trend and fluctuation on crop yields in northern China. Environmental monitoring and assessment 2017, 189, 532, doi:10.1007/s10661-017-6256-0.

Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript presents valuable information on the responses of winter wheat to drought in China.

The manuscript is well organized and, in general, so is its writing.

However, I do not understand the generic use of the term "winter wheat". Obviously, as the authors themselves indicated in lines 66-68 of the manuscript, different wheat cultivars may show a different response to drought. This is key in wheat improvement. Consequently, I believe that the cultivars used to determine this response should be indicated in the current study.

Author Response

Response to Reviewer 3 Comments

Thank you very much for your valuable comments and suggestions, which are very helpful to improve this paper. According to your comments, the manuscript was revised carefully and the detailed responses are listed as follows.

This manuscript presents valuable information on the responses of winter wheat to drought in China.

The manuscript is well organized and, in general, so is its writing.

Point 1: However, I do not understand the generic use of the term "winter wheat". Obviously, as the authors themselves indicated in lines 66-68 of the manuscript, different wheat cultivars may show a different response to drought. This is key in wheat improvement. Consequently, I believe that the cultivars used to determine this response should be indicated in the current study.

Response 1: Thank you for your advice. According to your suggestion, we have added a detailed description of the winter wheat cultivars in our study (Line183-Line187). Different wheat cultivars may show a different response to drought. To remove the effects of changes in wheat varieties, by the crop model calibration, we have obtained crop parameters that can represent the average condition of winter wheat varieties for many years in the NCP. This set of crop parameters remains unchanged throughout the simulation process, so that we can eliminate the impact of variety differences on the research results.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The manuscript was improved according almost all my comments. In my opinion, current version of the manuscript can be accepted for publication.