| In China,Huang-Huai-Hai Plain is one of the major food production region.As effected of global climate change,regional climate showed a trend of warming and drying.Drought and heat disasters occurred frequently,which affects the agricultural production and crop yields.This research adopts two indicators the standardized precipitation evapotranspiration index(SPEI)and extreme heat degree days(EDD)to analyze the spatial-temporal characteristic of drought and heat during summer maize growing season in Huang-Huai-Hai Plain.In addition,using the statistical data and combining with the model of APSIM to analyze the effect of drought and heat on summer maize yield.Main results are as follows:1.The occurring characteristics of precipitation and drought for summer maize in Huang-Huai-Hai Plain.The spatial-temporal distribution of precipitation was uneven for summer maize in Huang-Huai-Hai Plain from 1981 to 2015.There was less rainfall in the northwest and the most in the southeast.In different inter-decadals the precipitation for summer maize growing season was the most during 2001-2010.In different growing stages S-J,J-F and F-M,the proportion of precipitation in the whole growth period was 38%,25%and 37%,respectively.Over the whole crop growth season,the spatial distribution of precipitation decadal change trend was increased from northwest to southeast.The change trend was not significant in most regions of Huang-Huai-Hai Plain during different growth periods.The precipitation changes in the long-term period was not significant in this region.The frequency of drought in different growth stages was about 33%for summer maize season in Huang-Huai-Hai Plain from 1981 to 2015.The spatial distribution of drought showed a larger variation.In different inter-decadal the drought frequency was higher during 1981-1990.The spatial distribution of climate tendency rate for SPEI gradually increased from the northwest to the southeast during the whole growth season.North or southwest region showed a drying trend,but it was not significant,nevertheless,the southeast region showed a significant trend of humidifying.2.The occurring characteristics of heat and combined stress in Huang-Huai-Hai Plain.The spatial distribution of extreme heat days increased from northeast to southwest for summer maize in Huang-Huai-Hai Plain from 1981 to 2015,and the occurrence of heat was most frequent during the vegetative growth stage.The spatial distribution of EDD gradually increased from east to west in this area,and the EDD was highest during 2011-2015 in different inter-decadals during summer maize season.The EDD mainly accumulated in the period S-J(35.7?· d),which accounted for 56.5%of the whole growth period.In different growth stages,the change of EDD showed an increasing trend over Huang-Huai-Hai Plain.During the period S-M,the EDD increased significantly in most regions,and during the period S-J and F-M,areas where the EDD increased significantly mainly distributed in the north and east region,and during the period J-F,there was a significant increase of EDD in the local area of northeast and southeast.The occurrence characteristics of the combined stress of drought and heat in different stages ranked as J-F>S-J>S-M>F-M.Comparison of combined stress incidence among different inter-decadals showed that periods of 2006-2015 had a higher risk of combined stress of drought and heat than 1981-1990.3.Effects of drought and heat on summer mazie yieldThe type of drought and extreme heat year was SPEI<-0.5 and EDD greater than median values of EDD for each station in Huang-Huai-Hai Plain,its occurrence frequency was 23.18%from 1981 to 2014.This type of year led to the highest risk of production reductions,during which the year of detrended yield less than zero was about 58%.The correlation between detrended maize yield and SPEI during summer maize season was positive,and negative correlation between detrended yield and EDD.The result showed that drought and heat had led to a decline in maize yield in this region.The correlation analysis of detrended yield with SPEI and EDD indicated that period of J-F was the critical stage.A regression model of yield with SPEI and EDD was developed,which showed that one unit decrease of SPEI by reduced maize yield by 0.02%during summer maize season,and 10?· d increase of EDD reduced maize yield by 1.07%.The decadal influence of SPEI and EDD changes on yield indicated that SPEI tendency decreased maize yield by 0.02%and EDD tendency decreased yield by 0.82%.Maize production was more sensitive to variation of EDD tendency in different growth stages in Huang-Huai-Hai Plain from 1981-2015.4.Effects of drought and heat on summer mazie yield under different climatic conditions based on APSIM modelUsing the APSIM model to simulate the yield of different maize varieties Xundan 20 and Zhengdan 958 under normal climatic conditions in Wuqiao station from 1981 to 2017,the average yield for XD20 and ZD958 were 7590 kg ha-1 and 8358 kg ha-1,respectively,but the yield difference between varieties was not significant.Four climate scenarios were simulated,i.e.10%or 20%precipitation decrease and 1 ?or 2? Tmax increase.Simulated results showed that 20%precipitation decrease reduced maize yield the most.Further studied on drought and heat effects on maize yield over Huang-Huai-Hai Plain indicated that the changes in the single climatic factors of drought and high temperature lead to decreased production,but the yield reduction was not significant.The combined stress of drought and heat led to a sharp decline of maize yield in study region,which was more than the single variable.The yield level under combined stress was significantly lower than that under normal climate. |
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