Spatial Analysis of Urban Flood Vulnerability and the Role of Building Design in Flood Risk Reduction in Ogun State

Urban flooding represents one of the most pervasive and economically damaging hazards facing Nigerian cities, and the design of individual buildings and their relationship to flood-prone urban morphologies plays an underappreciated role in both increasing flood risk and offering mitigation opportunities. This study spatially analyses urban flood vulnerability in three flood-affected urban areas of Ogun State, Abeokuta, Sagamu, and Ijebu-Ode, and investigates the contribution of building design characteristics to flood risk reduction. Flood vulnerability was mapped using a composite index combining terrain slope analysis derived from LiDAR-corrected digital elevation model data, land use permeability analysis, historical flood event data obtained from the Ogun-Oshun River Basin Development Authority, and building exposure data from field survey of five hundred buildings. Building design variables documented include floor level above adjacent ground, foundation type, wall construction material, drainage connectivity, and window and door flood-sealing provisions. Statistical analysis examined the relationship between building design variables and flood damage scores derived from structured post-flood surveys of two hundred households. Results demonstrate that buildings with floor levels exceeding 600 mm above adjacent ground suffered significantly less damage across all flood events in the study period. Drainage connectivity between building plots and street drain systems significantly reduced internal courtyard flooding. Sandcrete block walls showed flood damage significantly above fired clay brick construction of equivalent age. The study proposes flood-resilient building design guidelines for Ogun State incorporating minimum floor level provisions, flood-tolerant material specifications, and drainage connectivity requirements for new residential developments in identified flood-risk zones. Keywords: urban flood vulnerability, building design, flood risk reduction, Ogun State, spatial analysis.