Assessment of Water Availability and Uses by using SWAT and WEAP models: the case study of Kilombero Basin Tanzania

Recently, the southern Agricultural corridor of Tanzania program and Kilimo kwanza initiative were introduced in the Kilombero basin as the best practices to expand agricultural productions. These initiatives resulted in the increase of population and expansion of agricultural activities which directly affects water demands and raise competition among the water users. The main aim of this study is to assess the water availability with respect to water uses in the Kilombero Basin specifically to assess water uses and consumption pattern, to quantify amount of water available and to assess water allocation scenarios. SWAT model was setup and calibrated in order to fill the gaps and extend the historical flow data so as to quantify water available in the basin. water evaluation and planning model (WEAP) was used to assess water allocation scenarios. SWAT model was successfully calibrated with the Nash efficiency of 0.64 and 0.75 coefficient of determination. The study identified five groups of water uses as domestic, industrial, environmental, livestock and agricultural uses. The current water available in the basin was estimated to be 1314.14 MCM [million cubic meters] in which total demand was 573.7 MCM. Agricultural, domestic, livestock, Environmental and industrial water demands comprise 81.53%, 3.06,06% and 1.80% respectively of the total water demand. Further, the study shows that the expansion of irrigation schemes and population growth by 2035 will increase the average annual demand by 81.85% and 41.54% respectively. The conclusion from the findings was that, the current water available is enough to meet current demands but for the 20 years to come unmet water demand will be experienced.