Research On Multivariate Flood Probability Distribution Of Flood Based On Copula Function

China’s water resources are unevenly distributed in space and time.Affected by global climate change,floods have brought great threats to people’s production and life.With the continuous development of society and economy and the improvement of water conservancy facilities,the loss of life and represented by casualties caused by floods,have decreased significantly in recent years.But the economic losses caused by it have remained high.Therefore,researching the multivariate probability distribution of floods and analyzing the possible joint distribution forms or rules have important theoretical significance and practical application value for flood damage and risk management.For the frequency combination method,when performing flood frequency analysis,there are difficulties in solving multi-dimensional problems and data distortion may occur during the solution.The Copula function is introduced to improve the frequency combination method.According to the advantage of Copula function that it is easy to construct a multi-dimensional joint probability distribution,combined with the function of frequency combination method in computing multi-dimensional problems.Established a risk estimation model for trunk and tributary flood encounters,and derived the downstream flood probability distribution expression after the main and tributary flood encounter.Taking the flood encounter in the upper reaches of the Yalong River as a research object and using the two-parameter 3D GH Copula function to estimate the flood risk in the upper reaches of the Yalong River Basin.Get the flood probability distribution after the encounter and the flood prevention risk rate of the flood control point.The calculation results provide a certain reference for downstream flood prevention work in the case of tributary flood encounters.For the current research on flood multivariable,most of the research is on two variables,and less research on three variables.Taking the annual maximum flood in the lower reaches of the Yalong River as the research object.The three variables of the peak,flood and flood duration of the annual maximum flood of the Yalong River were respectively combined with a two-variable combination and a three-variable combination.The Copula function was used to construct the flood multivariate probability distribution.The relationship between the probability distributions of flood variables is analyzed.Research on flood multivariate joint recurrence period and co-occurrence recurrence period.Obtain all combinations and most likely combinations of flood variables corresponding to different recurrence periods,and conclude that the joint recurrence period is less than the univariate recurrence period,and the co-occurrence recurrence period is greater than the univariate recurrence period.Research on the flood recurrence period of multivariate conditions,given the size of a certain variable,the recurrence period and change law of another variable are obtained.The research results provide some scientific basis for flood control security and risk assessment in the Yalong River Basin.