Characteristics Of Extreme Temperature And Precipitation In Heilongjiang Province And Its Effects On Spring Maize Yield

As an important production base and export base of maize in China,the frequent occurrence of extreme climate events in Heilongjiang Province seriously affects agricultural production and economic development.Previous studies on extreme climatic events have mostly focused on each season,but the study of extreme climatic events during each fertility period of maize is of great significance to cope with extreme climatic stresses in Heilongjiang Province.In this paper,we studied the spatial and temporal variation of extreme climatic events in Heilongjiang Province during each fertility period and their effects on maize yield by applying the percentile method,absolute threshold method,climate tendency rate,Pearson correlation,M-K nonparametric test and inverse distance spatial difference using daily observed temperature and precipitation data and maize yield data from 60 stations in Heilongjiang Province from 1961 to 2020.The main findings of the paper are as follows.The main findings of the paper are as follows :(1)For the extreme temperature index,temporally,TX90 p,TN90p,and T34 showed an increasing trend,TX10 p,TN10p,T8 showed a decreasing trend for the whole reproductive period and four reproductive periods of maize in Heilongjiang Province.Spatially,TXp90 and TNp90 showed the distribution characteristics of "high in the south and low in the north",TX10 p and TN10 p showed the distribution characteristics of "high in the north and low in the south",while T34 and T8 showed the distribution characteristics of "high in the west and low in the east" during the whole fertility period and four fertility periods of maize in Heilongjiang Province.TX10 p and TN10 p show a distribution of "high in the west and low in the east" and "high in the north and low in the south" respectively,but the spatial distribution of extreme temperature indices varies slightly in different generations.Meanwhile,there is some symmetry in the spatial and temporal distribution of extreme cold indices(TX10p,TN10 p,T8)and warm indices(TX90p,TN90 p,T34).(2)For extreme precipitation indices,temporally,CDD and CWD during the whole growth period of maize in Heilongjiang Province showed a slightly decreasing trend,but CDD in southwestern Heilongjiang Province and the Sanjiang Plain showed a significant decreasing trend.R95 p and SDII showed an increasing trend,and R10 showed a significant interdecadal increasing trend in the early 21 st century,while R10,R95 p and SDII showed a significant increasing trend in the Songnen and Sanjiang plains.The trend of R95 p and R10 increased in all four growth periods of maize,but only the seedling period showed a significant increase.Spatially,the CDD of maize in Heilongjiang province showed the distribution characteristics of "high in the eas t-west and low in the middle",CWD showed the distribution characteristics of "high in the middle and low in the east-west",and the spatial distribution of CDD and CWD showed a certain symmetry in all ages.R10,R95 p and SDII showed a distribution of "high in the southeast and low in the northwest",but with slight differences among different generations.The distribution of R95 p in the four growth periods differed significantly,R10 showed a distribution of "high southeast and low northwest".(3)Maize yield was negatively correlated with TN10 p and T8 in the whole growth period and four growth periods,negatively correlated with TX10 p,and TN90 p was significantly positively correlated.The correlations of TX90 p and T34 with maize yield in the whole growth and four growth periods varied among sites,but both indices were negatively correlated with maize yield in southwestern and eastern parts of Heilongjiang Province at the tasseling-milking period.CWD,R95 p,R10 and SDII were positively correlated with maize yield in southern Heilongjiang Province throughout the growth period.CDD was negatively correlated with maize yield in southwestern Heilongjiang Province.Maize yield was positively correlated with P95 and R10 at the seedling period and negatively correlated with R95 p and R10 at the jointing-tasseling,tasseling-milking and filling-maturity periods.(4)The weights of extreme precipitation indices were lower than those of extreme temperature indices in the whole growth period and four fertility periods,with the average weights of 18.24% and 81.76% in the whole fertility period and 6.84% and 93.16% in the four growth periods,respectively.However,the weight of extreme climate indices at different growth periods was not significant.However,there are some regional characteristics in the impact weights of extreme climate indices in different growth periods.The highest impact weights of seedling period are concentrated in the southwestern part of the Songnen Plain,the highest impact weights of jointing-tasseling period are concentrated in the northern part of the Sanjiang Plain,and the highest impact weights of filling-maturity period are concentrated in the Xiaoxinganling and the mid-mountain area of Mudanjiang.