Pluvial Flood Risk in Megacities under Future Climate and Demographic Scenarios

Sub-daily extreme precipitation can trigger severe flooding in urban catchments due to short hydrological response times. Although recent evidences show heterogeneous trends in magnitude and frequency across different regions of the world, rapid soil sealing from urban expansion – outpacing population growth – may significantly amplify pluvial flood risk. This study evaluates projected changes in pluvial flood risk for four megacities (population >10 million in 2010) under the Shared Socioeconomic Pathway-Representative Concentration Pathway (SSP-RCP) 2-4.5 and 5-8.5 from 2020 to 2100. Megacities are selected globally based on geomorphic flood-prone areas, identified through digital elevation and floodplain datasets, and on population hotspots derived from historical gridded data. Pluvial flood hazard is assessed using a DEM-based hierarchical filling-and-spilling algorithm, and compared against detailed hydrodynamic modeling. Vulnerability assessment is conducted at present-day for simplicity, while a data-driven algorithm for predicting future building footprints associated with future demographic scenarios is under development. Results provide insights into how climate and urbanization interact to cast future pluvial flood risk in the world’s largest cities, informing adaptation strategies for sustainable urban planning.