Spatial And Temporal Evolution Characteristics And Recurrence Period Of Drought In Ganjiang River Basin

In the context of climate change,the stability of the climate system has decreased,the characteristics of global and regional water cycle systems have undergone profound changes,and the form of drought has been severe.The Ganjiang River Basin,as the most economically viable region in Jiangxi,has been severely affected by drought in recent years.This article takes the Ganjiang River Basin as the research area,and uses the precipitation and temperature data of 39 meteorological stations from 1960 to 2018 to analyze the characteristics of precipitation and temperature changes in the Ganjiang River Basin in the past 59 years.The SPEI index was used to analyze the spatiotemporal characteristics of the basin's drought.Based on the two-dimensional Copula function,a drought risk assessment model for the Ganjiang River basin was constructed,the situation of the basin's drought risk was analyzed,and the impact of climate change on the basin's drought was studied.The main results obtained in this article are as follows:(1)The average annual temperature of the Ganjiang River Basin in the past 59 years has shown a significant upward trend,with an interannual change rate of 0.18°C/10 years,especially in the past 20 years since the 21st century,which has maintained a high average temperature.The average annual precipitation increased by 18.8mm/10 years,and the number of precipitation days decreased by 3.9 days/10 years.Nearly half of the precipitation was concentrated in April-June,and the spatial pattern of precipitation in the basin showed a pattern of "less than four weeks".The spatial and temporal distribution of precipitation is obviously uneven.The main cycle of the multi-year average temperature is 44 years,and the main cycle of the multi-year average precipitation is 35 years.(2)The seasonal drought in the Ganjiang River Basin is obvious,the range of autumn drought is large,and the degree of summer drought is more serious.The main cycle of annual drought index is 31 years,and the drought cycles of spring,summer,autumn and winter are 16,33,21 and 4 years respectively.The principal component analysis results of the drought index indicated that there were mainly spatial consistency,north-south differences,central and north-south differences in the drought time in the Ganjiang River Basin.Precipitation is the most important factor affecting the occurrence of drought in the river basin.The areas where the drought has increased since 2002 are similar to areas with less annual rainfall.(3)Use run theory to extract the duration and intensity variables of drought characteristics in the Ganjiang River Basin,and select the optimal edge distribution function by K-S test and q-q plot.The optimal edge distribution function of drought duration at each site has the most Weibull distribution,and the optimal edge distribution function of drought intensity has the most generalized extreme value distribution.There is a significant correlation between drought duration and intensity,and with the increase of drought duration and intensity in univariate recurrence period,the gap between stations' recurrence period also increases.(4)The d2 and AIC methods are used to evaluate the copula function.The optimal copula function of all stations in the Ganjiang River Basin is mainly Frank-copula.With the increase of drought duration and intensity,the joint recurrence period and transcendence recurrence period increased with different amplitudes.There is a significant difference between the joint recurrence period and the beyond recurrence period at the same site.The beyond recurrence period is always greater than the joint recurrence period.