Spatiotemporal Variation Of Wheat Yield In The Huang-Huai-Hai Region And Its Response To Extreme Climate Event

Extreme weather events occur frequently all over the world.The impact of climate change and extreme weather events on crop yield has attracted much attention.Huang-Huai-Hai region is the main producing area of winter wheat in China.Exploring the response of winter wheat yield to extreme climate events in this region is of great significance to ensure China’s food security.Studies have found that global warming has led to frequent occurrence of extreme weather such as drought,extreme high temperature and rainstorm.Climate warming will further reduce crop yield and even destroy crop reproductive structure.Relevant studies also found that the climate productivity of Winter Wheat in the Huang-Huai-Hai region increased in the south,decreased in the north,and the overall level decreased,and the decrease of precipitation may be the main reason for the decrease of climate productivity of winter wheat.Taking the Huang-Huai-Hai region as the main research area,based on the yield data in the statistical yearbook and the NPP data in the growing season from2001 to 2018,this thesis selects 14 indicators representing extreme climate,analyzes the temporal and spatial changes of extreme climate indicators and yield by using climate tendency rate,Sen-MK method,random forest model and Spearman correlation analysis method,and evaluates the importance and impact of various climate indicators on yield,Based on the evaluation results,the relationship between the main impact indicators and NPP in the growing season from February to May was established.The research draws the following conclusions:(1)During the study period of Huang-Huai-Hai region,extreme high temperature events occurred in 2014,extreme drought events occurred in 2011,and no significant years of extreme low temperature and extreme precipitation were found.The study area as a whole shows the characteristics of significant occurrence of high temperature compared with low temperature,insufficient precipitation and frequent drought.(2)In the study area,the temperature of winter wheat in the mature period(May)increased rapidly,and the warming trend was obvious.In May,the highest value of daily minimum temperature(TNx),warm nights(TN90p)and the lowest value of daily minimum temperature(TNn)showed a significant upward trend in different regions.TNx index showed an upward trend in all areas except the study area in the southwest of Henan,with a speed of about 0.8–1.3 ℃/10 a.The rising speed of TN90 p index at the junction of Jiangsu,Shandong,Henan and Anhui is about 7.5–11.5 %/10 a.The rising rate of TXn index in Anhui,Jiangsu,Shandong peninsula and the south is about 0.7 ℃/10 a.(3)In the study area,the precipitation intensity in Northern Anhui and southwest Henan decreased during the turning green period(February),and increased in Henan,Anhui and Jiangsu during heading and maturity(April and May).The index of days of extraordinarily heavy precipitation(R20mm)in February shows a downward trend in Northern Anhui and southwestern Henan,with a speed of about-0.3 d/10 a.In April,the rising rate of R20 mm index in Northwest Henan and South Hebei was about 0.4–0.5 d/10 a.In May,the rising rate of R20 mm index in southern Henan,most of Anhui and southern Jiangsu was about 1–1.2 d/10 a.The maximum 5-day precipitation(Rx5day)index in April rose at a rate of about 8.7–9.6 mm/10 a in northwestern Henan.(4)The junction of Shandong,Henan and Anhui and the southwestern part of Henan in the central part of the study area tend to be humid,and the south and north tend to be arid,but the humid conditions in Beijing,Tianjin and Hebei in the north are better than those in the south.From February to May,the sc＿PDSI index showed a downward trend at the junction of Shandong,Henan and Anhui and southwestern Henan,with a speed of about-2.7–-1.5 index value/10 a,and the downward trend weakened as the month went on.the sc＿PDSI index showed an upward trend in Beijing,Tianjin,Hebei and southern Jiangsu,with a speed of about 2.3–2.7 index value/10 a,and the upward trend increases with the passage of monthly sequence.In February,the SPEI03 index showed a downward trend in southern and southwestern Henan,with a speed of about-1.3–-1.1 index value/10 a.SPEI06 index showed a downward trend in Beijing and Tianjin and some surrounding areas in May,with a speed of about-1–-0.9 index value/10 a.(5)In terms of temporal and spatial changes of winter wheat yield,the winter wheat yield in the study area shows an upward trend as a whole,but the spatial distribution is uneven,mainly concentrated in Henan and Shandong,and the yield differences among cities are also obvious.NPP in the growing season can well reflect the changes of winter wheat yield.The annual fluctuation of NPP data in the growing season is large,which can reflect the response of yield to extreme climate events.(6)The response mechanism of winter wheat yield to the most important impact indicators(Rx5day,TNn,R20 mm,sc＿PDSI)in each month in the study area is as follows: the heavy precipitation in February is not conducive to the growth of winter wheat in northern Anhui,central and southwestern Henan,while The increase of precipitation and precipitation intensity in April is beneficial to the alleviation of drought in western Shandong,central and southwestern Henan,central and southern Hebei,southeastern Jiangsu,and southern Anhui.The increase of the minimum daily temperature in March is conducive to the accumulation of wheat active temperature in central and southern Hebei,northwest Shandong,southern and southwest Henan.There are spatial differences in the impact of drought on yield in May: for western Shandong,central and southwest Henan and central and southern Hebei,drought is conducive to the growth of winter wheat to a certain extent.The southeast of Jiangsu and the south of Anhui show that drought is not conducive to the production of winter wheat.(7)In view of the occurrence of extreme climatic events in the study area,the following suggestions can be put forward: First,breeding suitable wheat varieties in different regions.Drought and high temperature resistant varieties should be selected,and lodging resistant varieties should also be considered in Southwest Henan and other regions.Second,appropriate irrigation time can be selected according to the date of frequent high temperature and drought in different regions.