Global Assessment of Urban Flood Exposure and Multidimensional Resilience

Urbanization and climate change are reshaping the global landscape of urban flood exposure. However, existing assessments struggle to accurately evaluate the spatiotemporal dynamics, drivers, and urban adaptive capacity of future global flood exposure, largely due to overlooking the dynamic expansion of urban populations in tandem with physical boundaries, the lack of systematic quantification of uncertainties in climate-urban interactions under multiple scenarios, and the absence of comprehensive multidimensional resilience evaluations at the urban scale. Here, we developed an integrated framework coupling multi-scenario simulation of urban expansion and population distribution, multi-GCM driven flood hazard assessment, and multidimensional resilience evaluation to quantify the dynamics and uncertainties of global urban flood exposure, as well as its correlation with multidimensional resilience. We show that by 2050, the global urban population exposed to 1-in-100-year floods will rise from 588 million to 850 million. Urban expansion and population growth are the dominant drivers, contributing 71.4% of new exposure, significantly outweighing the impact of climate-driven floodplain expansion. Notably, the proportion of exposed population in future urban expansion zones is projected to be universally higher than in existing urban areas, a trend particularly acute in developing nations such as Vietnam. Further hierarchical regression analysis reveals a significant negative correlation between ecological resilience and exposure changes, validating the effectiveness of Nature-based Solutions in mitigating flood exposure. Identifying resilience deficits in 150 cities with significantly surging exposure, we advocate for a shift from reliance on singular engineering defenses to a multidimensional adaptation paradigm-incorporating strict urban growth boundary controls and ecological resilience enhancement-tailored to specific drivers to ensure global urban sustainability.