ABSTRACT
This study reports impact of climate change on water resources availability in the Sokoto-Rima river basin (SRRB). SRRB is located in the North Western Nigeria and spread across four (4) States (i.e. Sokoto, Kebbi, Katsina and Zamfara) with ninety three (93) Local Government Areas, with a human population of more than 15million. The study uses Water Evaluation And Planning (WEAP) model to asses and evaluate the impact of climate change on surface water availability and investigate the sensitivity of SRRB to climate change. This model allows the simulation and analysis of various water allocations and scenarios. The available data was used to model the surface water resources situation, and then projected in to the present situation of the existing hydraulic condition of the basin. The hydrological processes that occur for the six major rivers within the basin during 1970 to 2013 was satisfactorily modelled and calibrated by visual observation and compared with the measured data. The calibration process of the model was done using the first twenty years climatological records (1970-1990) and validated with the remaining eighteen years data (1990-2008). Simulations were proposed for various climatic situations considering the global climatic models (GCM) predictions and linear trend of the data. Six (6) selected climate change scenarios of temperature increases (0, +0.5, +1 oC) coupled with decrease or increases in precipitation (0,-10%, +10%) were combined and applied for the study area in the WEAP model for simulation. The model was used to analyse the linkage between the water availability and the demand in some selected sections within the basin. Base on the human population, the hydraulic situation of the basin was projected to the future to analyse the water availability up to the year 2064. The runoff, evapotranspiration, and water demand series were obtained as output of the model. Results showed that climate change will reduce viii the runoff, and increase evapotranspiration and water demand in the basin, more especially the demand for irrigation. Results also indicated an annual reduction in the total available water by about 1.70 billion cubic meter and a maximum monthly water demand of 17.11 billion cubic meter for the month of April (which is the driest month in the basin) for the selected sites, under 10% reduction in the actual rainfall within the basin and increase in evapotranspiration under 1oC increase in temperature, this indicate reduction of the surface water in the future for the basin. In addition, the dependency of the basin on surface water sources make it imperative to apply some methods of efficient use of water resources, to ensure future sustainability.