Assessment of Water Availability in the Sokoto Rima River Basin

摘要

The Sokoto-Rima River basin is located in the north western part of Nigeria, which comprise of four (4) states (i.e Sokoto, Kebbi, Katsina and Zamfara) and have population of more than 15million according to 2006 census. This makes the rivers and streams within the basin to be very important source of fresh water to the people living in those states. Therefore, even small decrease in runoff within the basin could have dramatic effects on the water supply of the region. This paper assesses and evaluates the impact of climate change on water availability and investigates the sensitivity of the basin to climate change in Sokoto-Rima river basin using the Water Evaluation and Planning (WEAP) model. This model allows the simulation and analysis of various water allocations and scenarios. The hydrological processes that occur for the six major rivers within the basin during 1970 to 2013 was satisfactorily model and calibrated by visual observation and compared with the measured data. The calibration process of the model was done using the first twenty two years climatological records (1970-1992) and validated with the remaining data (1993-2013). Simulations are proposed for various climatic situations considering the global climatic models (GCM) predictions. Six (6) developed climate change scenarios of temperature increase (0, +0.5, +1℃) coupled with decrease or increases in precipitation (0,-10%, +10%) were combined and applied for the study area in the WEAP model for simulation. Then, the climatically affected runoff, evapotranspiration, and water demand series were obtained as output of the WEAP model. Results indicate that climate change will significantly reduce the runoff, and increase evapotranspiration and water demand in the basin, more especially the demand for irrigation. The results indicate an annual reduction in the total available water of about 1.70 billion cubic meter and 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 1℃ 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 in the basin to ensure future sustainability. To adapt to the current trend and minimize the significant impact on availability of water supply in the basin in the foreseeable future, some proposed adaptation and mitigation measures to remedy this trend of scarcity ranges from sustainable developments to collaborative planning among the stakeholders within the basin.