Miami’s Coastal Flood Risk Under Climate Change: Abrupt Shifts Informed by Hurricane Irma

Severe tropical cyclones generate major marine hazards, including large waves and extreme water levels, which can lead to substantial coastal flooding, erosion, and associated socio-economic damages. Climate change—particularly sea-level rise—is expected to exacerbate these impacts by allowing hurricane-induced extreme water levels to penetrate further inland, thereby increasing flood risk in already vulnerable low-lying coastal areas.

This study first aims to accurately reconstruct the hazards, impacts, and risks associated with Hurricane Irma (2017), one of the most intense hurricanes to affect Miami (Florida, USA) in recent decades. Second, it examines how coastal flood risk may evolve if a hurricane with characteristics similar to Irma were to occur under different global warming scenarios. Particular emphasis is placed on identifying and characterizing potential abrupt shifts in future flood risk and their underlying physical and socio-economic drivers.

To achieve this, we adopt an integrated modeling framework that combines components often treated separately. Hydrodynamic processes—including storm surge, tides, and waves—are simulated using meso-scale models. These hydrodynamic outputs then serve as forcing for the 2D surfbeat version of the XBeach model, which simulates coastal flooding, erosion, and their interactions across the entire Miami region. Flood risk is subsequently quantified by coupling hazard outputs with exposure data for population and built capital. Climate change impacts are incorporated through scenario-based projections of sea-level rise and associated long-term shoreline retreat.

Results reveal a nonlinear escalation of coastal flood risk, characterized by two distinct critical thresholds. The first, affecting population exposure, emerges around +1.5 °C of global warming, when sea-level rise exceeds the imposed inundation threshold, allowing storm surge to propagate further inland. The second critical threshold, associated with economic damages, occurs near +5 °C of global warming and is driven by the near-complete permanent inundation of the Miami Beach peninsula.