Flood Vulnerability and Climate Adaptation of Maritime Built Heritage in Historic Shimoni Town, Southern Kenya Coast

Abstract

Coastal Kenya records the highest incidence of marine heatwaves in the western Indian Ocean basin, intensifying rainfall and flooding of historic monuments, buildings and archaeological sites. Despite growing concern over climate-related flooding in historic settlements, flood vulnerability assessment remains limited in Kenya. This study applied geospatial analysis to assess flood vulnerability in historic Shimoni Town using satellite imagery and Digital Elevation Models (DEM). Slope, elevation, flow accumulation, drainage density, Topographic Wetness Index (TWI), Topographic Position Index (TPI), and vegetation cover (NDVI) were integrated within a GIS-based Flood Hazard Index across the 40 km² study area. Limited hydrological datasets and flood inventories constrained calibrated weighting approaches; therefore, a linear combination method was adopted and validated through field observations, transect walks and expert consultations. Very gentle slopes (0–2.3°) contributed 44.11% of flood risk despite covering only 3.62% of the area. Low elevations contributed 28.82% of flood risk, while high drainage density (28.76%), high TWI (27.41%), low TPI depressions (27.34%), and high flow accumulation (26.33%) intensified flooding within low-lying zones. High NDVI zones (0.45–0.51) recorded high flood risk (21.67%), indicating that vegetation alone cannot offset unfavorable terrain and hydrological conditions. Highly susceptible areas included colonial headquarters, cemeteries, mosque ruins, jetties, and ritual cave entrances, whereas sacred Kaya forests, baobab and fig tree groves exhibited lower susceptibility. Findings show that flood vulnerability extends beyond individual monuments to interconnected hydrology–heritage systems, supporting recommended long-term watershed management, ecological restoration, planned retreat, and urgent interventions including contour drains, vegetated swales, permeable paving, and early warning systems. The study advances heritage climatology and represents the first DEM-based Flood Hazard Index application for maritime built heritage adaptation in Kenya.