This paper presents the assessment of impact of climate change on the runoff in the Kainji Lake basin. Hydro-meteorological variables within River Niger sub-basin in Nigeria and upstream countries were obtained from Nigerian Meteorological Agency (NIMET), Nigeria Inland Waterways (NIWA) and hydrological unit of Kainji hydropower station. The variables were subjected to regression and standardized anomaly indices (SAIs) analyses. The trend analyses revealed that all the hydro-meteorological variables in the locations exhibit fluctuations of different patterns. Precipitation, evaporation, minimum and maximum temperature depict upward trend, while the runoff and the water level depict downward trend in almost all the selected locations. The downward trends of runoff from upstream gauging stations confirm the continual reduction in the water resources of the River Niger sub-basin and the inflow into Kainji dam over the years, which eventually affect water availability for energy generation and other uses. The multiple regression model for Kainji hydropower station and other downstream stations such as Lokoja, Baro and Idah show that for every 1°C rise in temperature, runoff decreases by 4.45, 534.76, 12.72 and 159.05 m3/s respectively. SAIs also confirms significant decrease in runoff trend for the locations. The results also reveal that changes in climatic variables cause a tremendous fluctuation in runoff. The variation in runoff contributed by temperature, precipitation and evaporation for the stations ranged between 0.22 and 0.45 m3/s.
Key words: Climate variability, impact assessment, runoff, catchment management, Kainji Lake.