Joint distribution and risk of the compound disaster caused by rainfall and storm surge across Chinese coastal region

Coastal regions are extremely vulnerable to compound floods caused by extreme rainfall and strong storm surge. To improve the effectiveness of flood control measures in Chinese coastal cities and reduce the losses caused by urban compound flooding, it is important to analyze the joint probability of occurrence of extreme rainfall and strong storm surge and design the joint distribution function of daily storm surge and cumulative rainfall. In this study, we employed the Copula function to fit the joint probability distribution of storm surge and cumulative rainfall from 1979 to 2014. Then we used the Kolmogorov-Smirnov (K-S), Akaike Information Criteria (AIC), and Bayesian Information Criteria (BIC) statistical methods to obtain the optimal Copula function between storm surge and cumulative rainfall at each gauge alone the coast of China. Finally, based on the Copula method, we assessed the design value of compound scenarios of storm surge and rainfall in coastal China. The results indicate that the northern and southern parts of Chinese eastern coast have high frequency and the middle part has low frequency of compound disasters of strong storm surge and extreme rainfall. Western Guangdong, northern Fujian, southern Zhejiang, Shandong, and Liaoning provinces have a high frequency of compound disasters. Under the 50-year return period, the Beibu Gulf, northern Hainan Island, the coast of Zhejiang Province, and parts of the Bohai Bay have extreme rainfall and high storm surge. This study shows the temporal and spatial distribution of compound disasters of storm surge and rainfall in coastal China, and provides a framework for compound disaster scenario prediction.