Modelling climate change impact on the streamflow in the Upper Wabe Bridge watershed in Wabe Shebele River Basin, Ethiopia

Climate change affects the availability of water resources by altering the pattern and magnitude of precipitation, temperature, and streamflow. The projection of climate change impact on the streamflow is used to identify the level of changes and desirable intervention measures. In this research, Soil and Water Assessment Tool (SWAT) model and the regional circulation model (RCM) outputs of CORDEX-Africa climate model associated with mid and high-level Representative Concentration Pathways (RCP4.5 and RCP8.5) climate scenarios were used to evaluate the change in streamflow in two future projection scenarios (2041-2070 and 2071-2099). The study is directed to the Upper Wabe Bridge watershed found in the Wabe Shebele basin, Ethiopia. The result shows an increase in mean temperature by 3.46 and 5.15 degrees C for RCP4.5; and 4.78 and 5.88 degrees C for RCP8.5 in mid and long-term periods, respectively. The study also confirmed an increasing trend in annual precipitation by +26.3 and +31.85% for RCP4.5 and RCP8.5 climate scenarios, respectively, at the end of twenty-first century. In Kiremt (rainy) season precipitation shows an increasing trend by +44.28% and +59.34% for RCP4.5 and RCP8.5 climate scenarios, respectively, but Bega (dry) season show decreasing trend. The future projected annual streamflow shows increase trends under both climate scenarios in both projection periods. The mean seasonally streamflow decreases in the Belg (short rainy) season by -10.91% and increases in the Kiremt (rainy) season by 17.4%. Hence, the increment trend in streamflow during the Kiremt season will have the utmost significance for the requirement of storage and rainwater harvesting structures for irrigation development during dry season. Therefore, incorporating the possible effect of climate change is vital during water resources planning and development.