Climate Change Impact on Water Security in the Volta-Niger Basin Headwaters: An Integrated Hydrological-Environmental Engineering Perspective

This dissertation presents an integrated hydrological and environmental engineering analysis of climate change impacts on water security in the headwater catchments of the Volta-Niger basin shared between Nigeria's North West zone and Benin Republic, making original contributions to climate-hydrology coupling and water security assessment methodology for semi-arid West African catchments. The basin headwaters in Kebbi and Sokoto States provide critical recharge to both the Niger River and the cross-boundary aquifer systems shared with Benin, and projected changes in rainfall and temperature will alter both groundwater recharge and surface water availability with significant implications for irrigation, domestic water supply, and transboundary water relations. The dissertation employs a multi-model ensemble approach, downscaling six CMIP6 general circulation model outputs using both statistical and dynamic downscaling methods to produce climate scenarios for the 2050 to 2080 horizon under SSP2-4.5 and SSP5-8.5 pathways. Downscaled precipitation and temperature data drive a spatially distributed hydrological model of the 42,000-square-kilometre study catchment calibrated against stream flow, groundwater level, and satellite-derived evapotranspiration data. Environmental engineering assessment translates projected changes in stream flow, groundwater recharge, and flood and drought frequency into water security impact metrics including supply reliability for existing water infrastructure, groundwater level exceedance probabilities, and flood damage risk indices. The original theoretical contribution is a water security vulnerability typology for West African semi-arid catchments that disaggregates supply, quality, access, and governance dimensions in the climate change assessment. Adaptation engineering options are evaluated against the projected water security impacts. Keywords: climate change, water security, hydrological modelling, Niger basin, West Africa.