Urban growth prediction along Shared Socioeconomic Pathways (SSPs) for future flood exposure risk assessment: a cross-continental analysis of coastal cities

Abstract

Climate change remains a defining challenge of the twenty-first century, profoundly impacting ecosystems, economies, and human settlements. Among its consequences, the intensification of flood risks in coastal cities poses a critical threat to sustainable development, particularly in the Global South. This study bridges climate change-induced flooding scenarios with urban growth modelling, integrating Shared Socioeconomic Pathways (SSPs) into the SLEUTH model to simulate future urban trajectories and assess flood exposure under varying climate and socioeconomic conditions. Leveraging Earth observation information products, flood hazard scenarios based on Representative Concentration Pathways (RCPs) and high-resolution (30 m) urban growth projections, this study evaluates coastal, fluvial, and pluvial flood exposure for nine coastal agglomerations with diverse socioeconomic and environmental contexts. Urban growth projections under SSP1/RCP2.6, SSP2/RCP4.5, and SSP5/RCP8.5 scenarios reveal significant variability in urban expansion rates, with four cities projected to expand by over 50% by 2050. Flood exposure assessments for the target year 2050 reveal nuanced spatial and scenario-dependent patterns across all flood types: Surabaya (Indonesia) faces severe coastal flooding (up to 83 km2 under SSP5/RCP8.5), while Guayaquil (Ecuador) and Ho Chi Minh City (Vietnam) experience extensive risks of fluvial flood exposure, with over 37% of newly developed areas inundated in Guayaquil. Notably, the SSP2/RCP4.5 “Middle of the Road” scenario yields the lowest flood exposure in Khulna (Bangladesh) and Surabaya, whereas SSP1/RCP2.6 and SSP5/RCP8.5 project 30% to over 70% higher exposure in these cities. Disproportionate exposure to inundation in newly urbanized areas, particularly for Dar es Salaam (Tanzania) and Guayaquil, underscores potential risks associated with rapid and uninformed urbanization into flood prone regions. These findings emphasize the dual role of high radiative forcing climate scenarios and socioeconomic pathways in shaping flood exposure and associated risks, advocating for integrated strategies that combine climate mitigation with proactive, scenario-based urban planning.