Hydrological response and flood hazard mapping of the Ogun River Basin under projected climate and land-use change

This study provides an integrated assessment of future flood hazards in the Ogun River Basin under mid- and far-future scenarios (2044 and 2064) by combining climate projections and land-use dynamics within a coupled hydrological–hydraulic modeling framework. Using bias-corrected CMIP6 GCM projections (RCP 4.5 and RCP 8.5) and CA-Markov-based land-use projections were used with HEC-HMS and HEC-RAS models to simulate rainfall–runoff processes, peak discharges, and floodplain inundation. Climate-adjusted intensity–duration–frequency (IDF) curves were developed using ERA5 and CMIP6 data, revealing up to 39% increases in short-duration rainfall intensities under future scenarios. Peak discharge magnitudes rose by 30–74%, while flood extents expanded from 97.7 to 135.8 km2, and maximum inundation depths reached 4.8 m under RCP 8.5 far-future conditions. The ‘high’ and ‘very high’ hazard zones more than doubled, with vulnerable communities including Abeokuta, Sagamu, Ifo, Ikorodu, Kosofe, and Lagos Mainland. The study's novelty lies in its integration of climate and land-use change scenarios, the development of climate-adjusted IDF curves, and the coupling of hydrological and hydraulic models for multi-scenario flood mapping, filling gaps in previous basin-scale assessments that considered either climate or land-use change alone. The findings provide actionable insights for climate-resilient urban planning, updated design standards, and adaptive floodplains in rapidly urbanizing basins.