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

With climate change leading to sea level rise and 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 superimposed effects, greatly aggravating flooding. In addition, the influence of anthropogenic activities such as man-made flood control projects in coastal regions also need to be explored. Using the Ling River Basin on the east coast of China as a case study, this study investigated the impacts of natural and human drivers on the spatiotemporal distribution of extreme floods based on a 1D-2D coupled hydrodynamic model. The hydrodynamic model was calibrated and validated based on historical flood events, and the validated model was further used to reproduce the devastating flood caused by Typhoon Lekima in 2019. The 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 influences. The results also indicate that the high amount of discharge from the upper reaches of the Ling River was the main driver that caused the catastrophic consequences, and 83% of the inundation is caused by this factor. Comparatively, the failure of flood protection measures, which was a human driver, aggravated the influence of floods in local regions. Assessing the individual and superimposed effects of natural and human drivers on flooding may help enhance the resilience of flooded coastal areas.