Assessment of Effects of Climate Variability and Change on Water Availability Over Turkwel River Basin

Abstract

Climate has a major impact on the availability of water in arid and semi-arid regions. Rainfall is the primary source of water; yet, because of climate variability and change, it can be uncertain. This study evaluated how the Turkwel River Basin water availability had been impacted by climate variability and change. This study's main goal was to evaluate how the Turkwel River Basin's water availability is affected by climate variability and change. This was guided by specific objectives including; examination of the spatial characteristics of rainfall on turkwel river basin, examination of the temporal characteristics of rainfall on turkwel river basin, use of the Soil and Water Assessment Tool (SWAT) model to simulate streamflow over the Turkwel River basin, determination of temporal streamflow characteristics on turkwel river basin and determination of the relationship between rainfall and streamflow patterns and characteristics on turkwel basin. Data used in this study included both observed and gridded rainfall data, Simulated streamflow data (using; temperature data, Land use and land cover changes, solar radiation, wind speed soil map and digital elevation model (DEM) for present climate window (1981-2020) and future climate scenario, short term (2030s) and medium term (2060s) under RCP 4.5 and also under RCP 8.5). Methods used included; Validation methods (NRMSE), Standard anomaly Index and Mann-Kendell trend test, SWAT simulation, correlation analysis and regression analysis. Findings from the analysis showed that rainfall and streamflow characteristics at the annual timestep and seasonal time scales have been showing significantly increasing trends; MAM (Z = 0.49) and SON (Z = 2.49) for rainfall and MAM (Z = 2.94) and SON (Z = 3.95) for streamflow. Rainfall and streamflow are extremely volatile in both time as well as space which exhibits north-south variability gradient in the basin under present climate window and climate change scenarios. Coefficient of variation in terms of rainfall will be highest under RCP 8.5 centered 2060s (CV = 103.0%). Intra-basin linkage of rainfall and streamflow has been found to be high, (R2 = 0.718, 0.864 and 0.863); upper, middle and lower basin respectively. This study therefore recommends; setting up of an early warning system which would provide early warning information on variability of rainfall and streamflow; the study also recommends monitoring of streamflow along Turkwel river channel due to inadequate observed streamflow data necessary for calibration of SWAT model as well as its validation.