Evidence of increasing coastal flood risk along mainland China from 1985 to 2050: Perspectives on climate change and urban expansion

The rising sea levels and the increasing frequency of extreme coastal disasters, exacerbated by rapid urbanization in coastal areas, have led to more frequent and severe coastal flooding events. Yet, large-scale coastal flooding hydrodynamic modeling in mainland China remains limited, particularly due to inadequate consideration of driving factors, with most relying on the bathtub method. This study, considering the existing coastal protection standards, utilized the LISFLOOD-FP two-dimensional hydrodynamic model to simulate the spatial distribution of 100-year return period coastal flooding inundation under both the baseline and SSP5-8.5 2050 scenarios with higher accuracy and a spatial resolution of 90 m. In addition to climate change, we also conducted an in-depth analysis from the perspectives of urban expansion and coastal reclamation. The study finds that under the backdrop of rapid urbanization, settlement areas (1985–2015) and coastal reclamation zones (1990–2019) have expanded rapidly into flood-prone areas, especially in the 21st century, where the growth rate has greatly outpaced that of non-exposed areas. The area of settlement located in coastal flood hazard zones has increased 6.5 times, and the area of reclamation zones in coastal flood hazard zones has increased 26.3 times. Additionally, this study highlights the relative contributions of climate change and urban expansion to the future (SSP5-8.5 2050) coastal inundation risks in cities, providing valuable insights for the sustainable management of coastal flood hazards in China.