Hydrological Modelling Under Climate Change Scenarios for Water Resources Management in the Ogun River Basin Using Coupled Remote Sensing and Physically-Based Models

The Ogun River Basin is the primary surface water resource for Lagos and Ogun States, supporting municipal water supply, irrigation, and hydropower generation, yet the basin's hydrological response to projected climate change has not been characterised through physically-based modelling frameworks that adequately represent land surface heterogeneity at the basin scale. This dissertation couples remote sensing-derived land surface parameters with the SWAT hydrological model to simulate current and projected future water availability in the Ogun River Basin under CMIP6 climate change scenarios, making original contributions to West African hydrological science. Sentinel-2 land cover classification, SRTM topography, and a new remote sensing-derived soil hydraulic property dataset constitutes the land surface parameterisation. SWAT is calibrated and validated against discharge records at the Ogun Dam and three upstream gauging stations using SWAT-CUP sequential uncertainty fitting, achieving Nash-Sutcliffe efficiency values exceeding 0.78 for the calibration and 0.71 for the validation periods. Bias-corrected outputs from four CMIP6 GCMs under SSP2-4.5 and SSP5-8.5 scenarios are used as climate forcing for 2030-2060 projections. Results indicate projected mean annual discharge reductions of 12 to 34 percent by 2060 under SSP5-8.5, with particularly severe dry season flow deficits. The dissertation develops an original ensemble uncertainty disaggregation method that partitions total projection uncertainty into GCM structural, SWAT parameter, and climate scenario components. Findings are communicated to the Ogun-Osun River Basin Development Authority and the Lagos State Waterworks Corporation. Keywords: hydrological modelling, climate change, Ogun River Basin, SWAT, remote sensing.