It is commonly recognized that the vulnerability of coastal low-lying land tends to be exacerbated by climate change and socioeconomic development in a warmer future. However, the relative contribution of these two drivers to the future increase in inundation risk remains unclear. In this study, the future coastal flooding vulnerability is assessed for a typical tropical cyclone (TC)-prone, densely populated coastal city—Xiamen city, China—using TC intensities corresponding to 10-, 100-, and 1000-year return periods. For this assessment, a dynamic vulnerability index (DVI) is developed, which integrates inundation duration with other key parameters, including inundation depth, population density and GDP.
The results yield three main findings: (1) As TC intensity increases, the share of economic loss (E_loss) in total monetary losses declines from over 80% (10-year return period) to 39-56% (100-year return period) and further to 27-29% (1000‑year return period), while societal loss (S_loss) driven by population exposure becomes dominant under extreme events. (2) Socioeconomic development dominates the spatial expansion of flood risk, accounting for 60% of the total increase in risky areas. For monetary losses, however, the nonlinear interaction between socioeconomic development and climate change contributes 68% of the projected increase. Regarding total exposed population, climate change plays a dominant positive role, while socioeconomic development suppresses exposure due to future population decline. (3) A comparison with the Integrated Coastal Vulnerability Index (ICVI) reveals stark discrepancies: ICVI identifies a high-risk area just 3% the size of DVI’s and projects only a 20% increase in total risk by 2100. The difficulty in conducting this comparison further underscores the need for a standardized, monetized, and dynamic vulnerability framework to support meaningful cross-regional assessments.