Quantifying Urban Flood Exposure Using High-Resolution LiDAR Data and Census Disaggregation in Ibadan

Urban flood exposure quantification at household level requires high-resolution terrain data and spatially disaggregated population estimates that are currently unavailable for most Nigerian cities, creating a critical evidence gap in flood risk management planning. This study quantifies urban flood exposure in Ibadan, Oyo State, by integrating high-resolution airborne LiDAR terrain data with dasymetric census disaggregation techniques. A LiDAR-derived Digital Terrain Model at 0.5-metre resolution is used to parameterise the HEC-RAS 2D flood inundation model for the upper Ona catchment, generating inundation depth rasters for three return period events. Dasymetric mapping, informed by land use, building footprint density, and nighttime light intensity from VIIRS imagery, disaggregates ward-level NPC population estimates to 100-metre grid cells. Population exposure is computed by intersecting the gridded population surface with flood inundation rasters for each return period. Results indicate that approximately 420,000 Ibadan residents live in zones exposed to one-in-ten-year flood inundation, with the highest exposure concentrated in the Gege, Sanyo, and Odo-Oba floodplain communities. Vulnerability stratification reveals that low-income renter households constitute over seventy percent of the exposed population, underscoring the social dimensions of flood risk. The study contributes a methodological framework for fine-resolution flood exposure analysis replicable across other Nigerian secondary cities. Keywords: flood exposure, LiDAR, dasymetric mapping, Ibadan, urban flood risk.