Population Exposure to Flooding in Small Island Developing States Under Climate Change

Estimates of current and future population exposure to both coastal and inland flooding do not exist consistently in all Small Island Developing States (SIDS), despite these being some of the places most at risk to climate change. This has primarily been due to a lack of suitable or complete data. In this paper, we utilise a ~30m global hydrodynamic flood model to estimate population exposure to coastal and inland flood hazard in all Small Island Developing States under present day, as well as under low, intermediate, and very high emissions climate change scenarios (SSP1-2.6, SSP2-4.5 and SSP5-8.5). Our analysis shows that present day population exposure to flooding in Small Island Developing States is high (19.5% total population: 100-year flood hazard), varies widely depending on the location (3% - 66%), and increases under all three climate scenarios - even if global temperatures remain below 2°C warming (range in percentage change between present day and SSP1-2.6: -4.5% - 44%). We find that levels of flood hazard and population exposure are not strongly linked, and that indirect measures of exposure in common vulnerability or risk indicators do not adequately capture the complex drivers of flood hazard and population exposure in Small Island Developing States. The most exposed places under the lowest climate change scenario (SSP1-2.6) continue to be the most exposed under the highest climate change scenario (SSP5- 8.5), meaning investment in adaptation in these locations is likely robust to climate scenario uncertainty.