Assessment Of Drought Evolution In Zijiang River Basin

Drought is one of the natural disasters that cause heavy economic losses.It is frequent and regional.According to the statistical yearbook of hunan province,drought is mainly account for summer drought and autumn drought,with wide range and high frequency,Hunan province is surrounded by mountains on three sides,and the northern opening forms a unique climate condition,which leads to high temperature,sunny and hot with little rain in summer.Hengshao corridor is located in the hilly area with poor water storage capacity on the surface,and drought probability and drought degree are more serious than other areas.It is a prerequisite for drought early warning and drought risk management to study the characteristics of drought in the zijiang river basin and find the appropriate evaluation index for drought,in this paper,two drought assessment indicators SPEI and SPI were established based on the long-series hydrometeorological data,and four time scales were divided to analyze the characteristics of drought,and the drawning follow conclusions:(1)In SPI and SPEI values of the four scales,the longer the time scale is,the less influenced by precipitation factors,the more gentle the drought fluctuation is,and the more complete presentation.According to the m-k trend analysis of SPEI and SPI drought index,the mutation years between them were only one year apart,and the dry and wet change trends were relatively consistent,SPEI captures precipitation more accurately than SPI on different time scales.(2)Drought in the zijiang river basin has seasonal characteristics.In 55 years,drought in the whole region reached 20 times in winter,followed by 18 times in autumn,14 times in summer and 10 times in spring.The spatial evolution rule of seasonal drought is:spring drought frequency is between 6%-31%,especially in Anhua and Shaoyang stations,summer drought is between 26%-37%,especially in Dongkou and Longhui stations,autumn drought frequency is between 28%-35%,more serious in the east,winter drought frequency is between 9%-37%,more serious in the north.(3)Continuous no effective rainfall can analysis from the perspective of daily precipitation drought index,the drought monitoring and evaluation on the time scale is more fine,zi river basin,the four seasons arid regularities obtained based on the index 0-3 times each year for spring drought,0 to 8 times drought every year the summer,the autumn each year 0 to 5 times in drought,0 to 3 drought in winter every year.(4)Based on the analysis of seasonal drought periodicity characteristics of the basin based on the small wave square difference and real part,it is concluded that there are three obvious peaks in the evolution process of seasonal drought in the zijiang basin in spring,summer and winter.The first main cycle is 21 years,25 years and 45 years respectively,and there are two peaks in autumn.The first main cycle is 30 years.There are three types of periodic change rules of 18?32,8?17 and 3?7 years in all four seasons,and only the winter drought cycle has the whole region.