Economic losses from typhoon-induced coastal flooding in Hong Kong under future climate change

Typhoon Hato (2017), Typhoon Mangkhut (2018), and Typhoon Saola (2023) are among the most destructive typhoons to have struck Hong Kong in recent years, resulting in intense coastal flooding and severe damage. However, comprehensive flood risk assessments remain limited due to scarce data from inundation field surveys and damage assessments. In this study, we develop an integrated framework combining a wind-pressure model, a hydrodynamic model, and a depth-damage function to estimate coastal flood hazards from tropical cyclones in Hong Kong. This framework incorporates worst-case scenarios of extreme tidal levels and sea level rise. We simulate coastal water levels and validate them against station observations, achieving Nash-Sutcliffe efficiency coefficients of 0.70–0.88. Our findings highlight that, the northwestern region of Hong Kong (Yuen Long District) is the most vulnerable to coastal flooding. In the case of Typhoon Hato, the effects of extreme high tide and sea level rise are comparable in their contribution to coastal flooding. In contrast, for Typhoon Mangkhut and Typhoon Saola, extreme high tide has a more pronounced impact on exacerbating flooding. The worst-case scenario, combining extreme tides with sea level rise under SSP585, could amplify economic losses by 1.3–1.5, 1.7–1.9, and 2.0–2.3 times for the three typhoons. Residential areas are particularly vulnerable, with inundated area and economic losses approximately twice those of industrial and commercial buildings, respectively. This quantitative risk assessment can support the government in implementing effective flood prevention measures and optimizing land use planning, potentially reducing economic losses in coastal areas.