Analytical Framework for Urban Flood Risk Mapping Using Hydraulic Modelling and Remote Sensing in Ibadan, South West Nigeria

This study develops and applies an analytical framework for urban flood risk mapping in Ibadan, South West Nigeria, integrating two-dimensional hydraulic modelling with high-resolution remote sensing data to produce spatially explicit flood hazard maps at the neighbourhood scale. Urban flood risk mapping is a critical input to disaster preparedness, land use planning, and infrastructure prioritisation in flood-vulnerable Nigerian cities, yet the technical methodologies used in existing Nigerian flood maps are insufficiently rigorous for detailed planning decisions. The framework integrates LiDAR-derived digital elevation model data, land cover classification from Sentinel-2 satellite imagery, hydrological catchment delineation, and updated intensity-duration-frequency relationships derived from thirty-five years of Ibadan rainfall records into a MIKE FLOOD coupled one-dimensional and two-dimensional hydraulic model. Model calibration used water level records from the 2017 and 2020 flood events. Scenarios were simulated for the five-year, twenty-five-year, and hundred-year return period design storms, and flood inundation extents, depths, and velocities were mapped for each scenario. Risk maps were produced by combining flood hazard maps with a building exposure layer and a social vulnerability index derived from census data. Results delineate 28 square kilometres as high-hazard flood zone under the hundred-year event, with significant areas in Bodija, Agodi, and Oja-Oba communities showing modelled depths exceeding one metre. The integrated risk maps identify fourteen neighbourhoods with high combined hazard and vulnerability scores. The study provides a transferable methodology for flood risk mapping in other Nigerian cities. Keywords: flood risk mapping, hydraulic modelling, urban flooding, Ibadan, remote sensing.