Coupling A Copula Function And The Jensen Model To Construct Regional Agricultural Drought Risk Assessment With Multiple Return Periods

Drought is the most complicated natural phenomenon.Since the 20 th century,global warming has accelerated,and droughts have increased in scale and frequency.China has become one of the regions with the most frequent and devastating natural disasters,and the drought risk of crops is the first of all kinds of natural disasters.Affected by various natural and social factors,the methods and approaches of regional agricultural drought risk assessment have always been the focus of disaster scholars.Southwest China is dominated by karst landforms,which is restricted by unstable monsoon climate and large terrain height difference.It is a region with frequent drought and natural disasters in China,which is very harmful to crops.The paper takes Zunyi City as an example,which is the most typical City of karst landform development.The monthly precipitation data set of ground meteorological observation stations in Zunyi City from 1956 to 2020 was selected,and the drought characteristic variables were extracted by the coupled use of the precipitation anomaly percentage(Pa)index and the theory of runs.The Copula function was applied to establish the joint distribution model of characteristic variables,obtaining the drought frequency.Combined with the Jensen model,the agricultural drought loss rate was calculated.By establishing the risk curve of "joint occurrence probability ～ agricultural drought loss",the joint Copula function and Jensen model are combined to construct a regional agricultural drought risk assessment model with multiple return periods,and the results are compared with those of the traditional typical year selection method to verify the rationality of the model,thus providing new ideas for regional agricultural drought risk assessment.The main research results are as follows:(1)The loss caused by drought under a certain drought resistance condition can be quickly estimated.By combining the joint occurrence probability calculated by Copula function with the agricultural drought loss rate calculated by Jensen model,the possible losses caused by different frequency droughts in a certain area under a certain drought resistance condition can be quickly estimated by constructing the drought risk mechanism relationship curve.This method is helpful for drought authorities to make scientific decisions,respond in time,and formulate appropriate and effective countermeasures.(2)The idea of risk quantification in drought risk assessment is broadened.Through the established relationship curve between the joint occurrence probability and the drought loss rate,the drought loss rate corresponding to different joint occurrence probabilities is derived.The joint occurrence probability is converted into the drought return period,and the spatial distribution map of drought loss under different drought return periods can be obtained.Drawing the spatial distribution of agricultural drought losses under different return periods is helpful to compare the vulnerability between regions at a macro level,so that the competent departments of drought resistance can actively prevent and respond to risks.This method broadens the space for subsequent utilization and provides ideas for risk quantification in drought risk assessment in the future.(3)An agricultural drought risk assessment model based on drought event process was developed,and a set of agricultural drought risk assessment technology process was formed,which is conducive to the realization of agricultural drought pre-assessment and post-disaster rapid assessment,and enhances the effectiveness.It can provide scientific reference for scientific management and reasonable and effective disaster prevention and mitigation programs.