Mapping tomorrow’s flood: a probabilistic, equity-centered risk assessment for the Indianapolis Metropolitan Area

Abstract Urban flooding is an increasingly critical challenge under climate change, driven by intensifying precipitation, land use change, and deepening social vulnerability. This study presents a combined, high-resolution framework to characterize and map current and future urban flood risk in the Indianapolis Metropolitan Area (IMA). We combine probabilistic hazard modeling using stochastic precipitation simulations, physically based surface runoff estimation, and a composite flood risk index (CFRI) that integrates social poverty vulnerability and exposure. By capturing the full range of plausible rainfall scenarios, this approach provides a spatially explicit, comparative assessment of how interactions between these components may shift under future climate and socioeconomic scenarios. Results reveal that climate change will substantially intensify and redistribute flood risk across the IMA, particularly under the RCP 8.5–SSP5 scenario. Very-high CFRI zones increase sevenfold by century’s end, with significant new risk emerging in previously low-risk suburban areas, while poverty-driven vulnerability deepens in peripheral communities. These findings highlight the limitations of hazard-only assessments and underscore the importance of integrating socioeconomic dimensions and uncertainty into urban flood risk analyses. The resulting high-resolution risk maps can guide policymakers in targeting adaptation investments, prioritizing vulnerable populations, and designing equitable resilience strategies that respond to both current and future risk dynamics.