Current and Future Flood Risk from Tropical Cyclones in Puerto Rico Under 1.5°C and 2°C Climate Change

Small Island Developing States are some of the most at risk places to flooding caused by tropical cyclone rainfall. However, there is a mismatch between existing flood risk assessment in small islands, and the increasing severity of projected tropical cyclone rainfall under current and future climate change. This research aims to address this gap by presenting the first application of an event-based rainfall-driven hydrodynamic model in a small island, for the Caribbean island of Puerto Rico. Applying an event set of 59,000 synthetic hurricane rainfall events, we represent hurricane rainfall spatially (~10km) and temporally (2-hourly), estimating flood hazard and population exposure at the island scale (9,100km²) at 20m model resolution using hydrodynamic model LISFLOOD-FP. Using this event-based approach, we aim to understand: i) what are the current estimates of population exposure to flooding from hurricane rainfall in Puerto Rico; and ii) how do these risk estimates change under 1.5°C and 2°C climate scenarios. We find that current population exposure to flooding from hurricane rainfall in Puerto Rico is high (8-9.80% of the population every 5 years), with an increase in population exposure of 1.60-15.20% and 0.70-22.30% under 1.5°C and 2°C climate change. This has critical implications for adaptation to more extreme flood risk in Puerto Rico, as well as underlining the important implications of the 1.5°C Paris Agreement target for small islands – a finding that is likely to be applicable to other small islands affected by tropical cyclones.