Coupled Atmospheric-Hydrological-Agricultural Modelling for Climate Change Impact Assessment on Nigerian Irrigation Systems

This study develops a coupled atmospheric-hydrological-agricultural modelling framework to assess the impacts of climate change on Nigerian irrigation system performance over the period 2025 to 2075, providing detailed irrigation infrastructure planning implications. Climate change is altering both irrigation water supply, through changes in river flows and groundwater recharge, and irrigation water demand, through rising evapotranspiration and shifting growing seasons. Assessing the combined supply-demand impact on irrigation system performance requires modelling frameworks that explicitly couple climate, hydrology, and crop systems, which no existing study has applied comprehensively for Nigeria. This study couples a dynamically downscaled regional climate model output from the CORDEX-Africa ensemble with the SWAT hydrological model for three major river basins, the Hadejia-Jama'are, Benue, and Imo-Anambra, and the AquaCrop crop model for the major irrigated crops in each basin. Irrigation system performance under business-as-usual and adaptive management scenarios is simulated under three RCP emission pathways. Findings reveal that under RCP 8.5, irrigation water availability in the Hadejia-Jama'are basin is projected to decline by 31 percent by 2060 while irrigation demand increases by 28 percent, creating a 59 percent gap between water supply and demand without adaptation. Southern basins show less severe but still significant impacts. Adaptation measures including improved water use efficiency, crop variety switching, and irrigation expansion show partial but insufficient compensating effects. The study contributes original coupled modelling evidence for Nigerian irrigation planning and recommends immediate development of a national irrigation climate adaptation strategy.

Keywords: coupled modelling, climate change, irrigation systems, Nigeria, water scarcity.