Escalating coastal flood risk and impact thresholds in Miami revealed by Hurricane Irma

Abstract Tropical cyclones cause severe coastal flooding and erosion—impacts amplified by climate change-driven sea-level rise. Hurricane Irma (2017) was one of the most destructive hurricanes affecting Florida, including Miami, causing widespread coastal flooding. This study assesses how coastal flood risk would evolve if a hurricane similar to Irma occurred under sea-level rise conditions, with a focus on identifying potential impact thresholds, defined as non-linear changes in future flood risk. To this end, we first reconstruct the baseline coastal flood risk associated with Irma by integrating hydrodynamic simulations, coastal impact modelling (flooding, erosion, and their interactions), and risk assessment considering population and built capital. We then project future conditions by incorporating sea-level rise and the associated long-term shoreline retreat. Scenario-based projections reveal non-linear escalation in coastal flood risk, with two distinct impact thresholds. The first, related to affected population, emerges around + 1.5 °C of global warming, when sea-level rise surpasses the minimum flood-depth threshold, enabling storm surge to penetrate further inland. The second, related to economic damages, occurs near + 5 °C, driven by the near-complete permanent inundation of the Miami Beach peninsula. These findings highlight the escalating threat of hurricane-driven flooding under climate change and the pressing need for coastal adaptation.