Development of a land-river-ocean coupled model for compound floods jointly caused by heavy rainfall and storm surges in large river delta regions

Abstract

The simultaneous or sequential occurrence of different flood processes, including extreme storm surges and heavy precipitation, tends to trigger compound floods, which are often destructive to life and property. However, numerical models that fully represent the effect of various flood processes and their interactions have not yet been firmly established. In this study, a coupled land-river-ocean model is developed that considers storm surges, storm waves, astronomical tides, river flow, and precipitation. The coupled model is applied to the simulation of compound floods induced by tropical cyclones in the Pearl River Delta. The numerical results obtained on river flow and ocean surface elevation are shown to agree well with observations for cases considered, with Willmott skill values of 0.96 and 0.88, respectively. The coastal inundation area obtained with the model covers approximately 80 % of the area identified by remote sensing. An attribution analysis implies that ocean processes contribute to more than half of the total flood volume, while precipitation accounts for 5 % to 15 % through a tropical cyclone event in the Pearl River Delta region. Significantly, the contribution of river base flow varies from 2 % to 30 % depending on the landfall time of the tropical cyclone. It is also emphasized that the completeness of the coupling method substantially affects the numerical accuracy.