Assessment of coastal vulnerability to sea level rise: a case study of the Kenyan coastline

Introduction: Kenya's 640 km coastline faces escalating exposure to sea-level rise, yet no integrated, spatially explicit assessment combining physical and socioeconomic vulnerability exists for the entire national coastline. This study addresses that gap by developing the first GIS-based Coastal Vulnerability Index (CVI) at national scale using exclusively open-access data.Methods: The shoreline was divided into 7,555 segments of approximately 200 m, each attributed with eight physical indicators (including shoreline change rate, coastal elevation, geomorphology, bathymetry, and sea-level rise trend) and three socioeconomic indicators (population density, land use/land cover, and distance to coastal infrastructure). Indicators were ranked on a 1–5 ordinal scale and weighted using the Analytical Hierarchy Process (CR = 0.046 and 0.033 for physical and socioeconomic sets respectively), then aggregated into a Physical Vulnerability Index (PVI) and Socioeconomic Vulnerability Index (SoVI), each normalised to a 0–100 scale and combined into the final CVI.Results: Overall, 31.7% of coastal segments fall in the High or Very High CVI class (mean CVI = 51.66). The most vulnerable stretches are concentrated along the Kilifi–Malindi corridor, where active erosion and sandy geomorphology coincide with elevated socioeconomic exposure, and near the Mombasa urban core. An at-risk inventory of 46 heritage sites, hotel facilities, and biodiversity areas shows that all mapped heritage sites fall in the High or Very High CVI class, with a mean CVI of 74.14.Discussion: The elevated socioeconomic vulnerability relative to physical vulnerability underscores the role of human exposure in driving composite coastal risk in Kenya. The open-data framework developed here provides a transferable, replicable baseline for evidence-based coastal adaptation planning in Kenya and comparable data-constrained regions of East Africa.