Assessment of effects of natural and anthropogenic drivers on extreme flood events in coastal regions

Abstract With climate change leading to sea level rise and the frequent occurrence of extreme weather events, extreme flood disasters occur frequently in coastal cities, especially under the combined influence of heavy rainfall, fluvial floods, and storm surges. Compound floods from multiple sources are prone to superimposing effects, greatly aggravating the flooding. In addition, the influence of anthropogenic activities such as man-made flood control projects in coastal regions also need exploring. With Ling River Basin in the eastern coastal area of China as the case study, this study investigated the impacts of natural and human drivers on the spatio-temporal distribution of extreme floods based on a 1D- 2D coupled hydrodynamic model. The hydrodynamic model was calibrated and validated based on historical flood events, then validated model was further used to reproduce the devastating flooding of Typhoon Lekima in 2019. Results show that the model has great capability and accuracy in simulating both the flood occurrence process and its inundation extent under natural and anthropogenic influence. It also indicates that the huge amount of discharge from the upper reaches of the Ling River was the main driver that caused the catastrophic consequences. Comparatively, the failure of flood protection measures (FPM), which was a human driver, aggravated the influence of floods in local regions. By assessing the individual and superimposed effects of natural and human drivers on flooding is helpful to enhance the resilience of flooded coastal areas.