ASSESSMENT OF FUTURE WATER AVAILABILITY FOR IRRIGATION AND DOMESTIC NEEDS IN MBARALI RIVER WATERSHED

Abstract

Water availability for various usages in the Mbarali River Watershed (MRW) of the Usangu plain in Tanzania, has been reduced due to the decrease in water flow caused by uncertain rainfall, irrigated agriculture expansion, rapid population growth, urbanization, and changing lifestyles. This research aimed at assessing water availability under climate change for current and future irrigation and domestic needs in the Usangu plain. To assess future water availability, the study used the Soil and Water Assessment Tool (SWAT) model. The SWAT-Calibration Uncertainty Programs (SWAT-CUP) with the global sensitivity technique within Sequential Uncertainty Fitting II (SUFI-2) were utilized to calibrate, validate, and analyze the sensitive parameters for river flow simulation. The model performed nicely on a monthly scale having determination coefficient and Nash-Sutcliffe values greater than 0.7. Based on the two Representative Concentration Paths (RCPs) indicated in the IPCC Fifth Assessment Report, the study use bias corrected CORDEX data and calibrated SWAT model to estimate future streamflow in the MRW from 2031 to 2070. Additionally, the observed streamflow results did not show a significant increasing trend, and future streamflow in the MRW is likely to increase under RCP4.5 but decrease under RCP8.5.