Amplification of flood risks by the compound effects of precipitation and storm tides under the nonstationary scenario in the coastal city of Haikou, China

This study assess the compound flood risk in Haikou - a coastal city in China. Knowing the potential change of the compound flood risk caused by precipitation and storm tides is valuable for coastal flood risk reduction. The study, explored the compound flood risk by integrating the hydrological model and copula-based design of precipitation and storm tides. The varying parameter distribution (VPD) model, copula model, and the most-likely weight function were used to obtain the combined design values of precipitation and storm tides under the nonstationary scenario. The combined design values were applied to the boundary conditions of the 1D-2D hydrological model. Subsequently, the change of the bivariate RPs, design values, and compound food risks were investigated under the nonstationary scenario.

The results show that:

1. The bivariate RP of precipitation and storm tides decreases significantly under the nonstationary scenario, and the combined design values are significantly increased when considering the impact of the nonstationary scenario.
2. The compound flood risk has been significantly increased under the changing environment.
3. The compound effects of precipitation-storm tides would have a greater influence on the food risk when the bivariate RP is more than 50 years, and the peak time lags significantly impact the compound food risk.

The methods and results of this study can be used as a reference for other coastal cities.