Enhanced understanding on spatial and dependence properties of rainfall extremes and storm tides in coastal cities

To evaluate the coastal flood risk, it is essential to study the spatial properties of rainfall extremes and the effects of storm tides. This paper investigates the spatial analysis of extreme rainfall across different coastal cities and examines the dependence analysis between rainfall extremes and storm tides. A bivariate threshold excess model and an enumeration method were employed to conduct the spatial analysis and dependence study. Focusing on the Modaomen estuary in Zhuhai City within the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), which plays a crucial role in the economic development of China, this research analyzes observed data from one tide station and eleven rainfall stations. The main findings are as follows: (1) the number of joint events from multiple rainfall stations consistently exceeds the expected outcomes under null hypothesis; (2) increasing the duration enhances the strength of extreme rainfall dependence and reduces spatial variability; (3) the region is prone to the combined effects of rainfall extremes and storm tides, with storm tides showing the highest dependence on 24-hour duration extreme rainfall; and (4) this dependence strength significantly increases at the typhoon season between July and September. The proposed method and its findings offer an in-depth understanding and quantification of coastal urban flood risk within the GBA of China.