Study on the Joint Probability and Return Period of Extreme Precipitation in Baoji Area Based on Copula Function

The Copula function can quantitatively assess the risk of extreme precipitation under different joint return periods. Taking Baoji area as an example, six extreme precipitation indicators were selected, and the preferred edge distribution function was tested by K-S, AIC, BIC and RMSE criteria. The results showed that: the Copula function can be used to perform bivariate fitting. While the Gaussian-Copula function could better fit the joint probability distribution of the extreme precipitation index and the risk assessment of extreme precipitation under different joint return periods of extreme precipitation index in Baoji area. The risk of extreme precipitation events in Taibai and Meixian was higher in high and low scales, respectively. R95P, R99P, R×1day and R×5 day of extreme precipitation index in Meixian had the fastest growth rate, had the smallest growth rate in Taibai, and PRCPTOT in Meixian only showed a significant increase trend. Spatially, the increase area of PRCPTOT, R×1day and R×5day accounted for 65-82% of the total area. Under SSP4.5 and SSP8.5 emission scenarios of CMP6 climate model, the extreme precipitation index will be an increase trend, and have increase significantly after the 2060s. The studies provide a basis for government decision-making, disaster defense planning.