The Applied Research On Drought Analysis By SEM And Copula Functions

Rapid population growth and rapid economic development have made an increase in human impact on various disaster systems."Natural disasters can no longer simply be understood as ‘natural' disasters".This article selects three regions(Chongqing City,Henan and Heilongjiang Province)as the research area,which in environmental climate,geographical features and the types of agriculture and so on various aspects show the great difference,regional drought vulnerability assessment and analysis of characteristics of drought.Pelanda has said that disasters reflect the vulnerability of the society,and it's the result of the destruction to the fragile environment caused by the risk factors beyond its capacity to respond.The extent of damage caused by disasters depends not only on the intensity of the disaster,but also on the vulnerability of the environment itself.The difficulty of studying drought vulnerability lies in selecting its evaluation index,which focuses on constructing an effective and concise index system of regional drought vulnerability assessment.And on the basis of the monthly precipitation and temperature data of three places,using copulas connect function to establish two-dimensional joint distribution of drought characteristics variables,depicting the drought characteristics(The recurrence period of drought duration and drought intensity),and predict the two-dimensional return period of drought characteristics,so as to provide data support for active prevention and treatment of agricultural drought risk.Firstly based on the original evaluation index data of vulnerability in the three regions from 2003 to 2015,the paper selects the vulnerability evaluation index system by the structural equation model method,the results showed that the index optimization rate of Chongqing City,Henan and Heilongjiang Province was 61%,50% and 40% respectively,its goodness-of-fit is better than the evaluation system build by the original indexes.The verification and analysis process of evaluation index indicates that the number of livestock per unit area at the end of the year will have an important influence on the accuracy of vulnerability assessment.The agricultural drought vulnerability composite scores in study area by principal component analysis method showed that from 2003 to 2015,agricultural drought vulnerability was increased and then decreased in Chongqing City,while Henan Province showed great fluctuation,and the agricultural drought vulnerability in Heilongjiang Province generally showed a decrease trend.The study area in the region have different focus on the influence factors of agricultural drought vulnerability,such as greater dependence on water resources in Heilongjiang Province,and a greater reliance on drought resistance capability in Henan Province.Secondly,the drought SPEI index was constructed by using meteorological data of three regions from 1997 to 2016.The drought duratino,drought intensity and drought vulnerability in Chongqing City,Henan Province and Heilongjiang Province were subjected to logistic distribution,log-normal distribution and normal distribution.The joint distribution model of drought characteristics in Chongqing City and Henan Province is GH Copula function,and in Heilongjiang Province is the Frank Copula function.The forecast results show that the D-S portfolio return period structure is similar in Chongqing area and Henan Province,while the recurrence period Heilongjiang Province is a bit smoother than the other two areas.