Sea-level rise and population development drive future exposure to coastal flooding in Seychelles

Abstract Small Island Developing States (SIDS) are among the most vulnerable regions to sea-level rise (SLR) and coastal climate hazards, which pose increasing threats to populations, economies, and critical infrastructure. Seychelles face mounting risks from coastal flooding and erosion, yet detailed assessments of future climate impacts to inform national policy remain limited. This study evaluates future impacts of SLR-induced coastal flooding in Seychelles using high-resolution hydrodynamic modelling combined with socio-economic projections based on the Shared Socioeconomic Pathways (SSP). We simulate extreme water level events under three SLR scenarios (SSP1-2.6, SSP3-7.0, and SSP5-8.5) from 2030 to 2150 and assess exposure of population, buildings, and road networks on the islands of Mahé, Praslin, and La Digue. Our results indicate a sharp rise in land, population, and infrastructure exposure to an extreme water level event across all scenarios: Mahé is projected to face population exposure of up to 16,200 people by 2100 under SSP3-7.0, and over 150 km of roads will be at risk of flooding from by 2150, while Praslin and La Digue show delayed but accelerating exposure later in the century. Crucially, scenarios with high population growth show intensification of potential risks, sometimes surpassing the higher sea-level scenarios with lower demographic pressure. These findings can inform climate resilient planning and coastal adaptation policies in Seychelles and underscore an urgent need for integrated adaptation strategies. Without proactive implementation of measures, SLR could have large impacts on Seychelles’ economy. Our subnational projections demonstrate the type of evidence that is required for supporting adaptive governance in order to safeguard SIDS against escalating climate risks.