CLIMATE CHANGE IMPACT ON STREAM FLOW (A CASE OF KATAR CATCHMENT, RIFT VALLEY BASIN, ETHIOPIA)

Abstract

Climate change significantly alters many hydrological conditions, which in turn affects the water resources and stream flow. The uncertainty of the availability of water resources will affect agricultural production and challenge socio-economic systems to feed the growing population. Therefore, this study was investigated to assess the potential impacts of climate change on streamflow of katar river catchment in Central Rift Valley basin, Ethiopia. Ensembles of coordinated regional climate downscaling experiment (CORDEX)-Africa under two Representative Concentration Pathways (RCP 4.5 and RCP 8.5) has been used to downscale the daily precipitation, daily maximum and minimum temperature of the study area. The observed meteorological variables and downscaled CORDEX Africa climatic data were corrected with distribution mapping (DM) method. The SWAT hydrological model was used to perform stream flow simulation. The trends of precipitations and temperatures in the basin were assessed by comparing the baseline Period (1986-2005) and future scenarios 2021-2040 (2030s) and the 2051-2070 (2060s). The trends of mean annual Precipitation were projected to decrease under RCP4.5 by 17.8% and 26% for the 2030s and the 2060s, respectively. Likewise, for RCP8.5, the average annual precipitation decreases were found to be 19% in the 2030s and 10% in the 2060s. The trends of monthly maximum temperatures were projected to increase under RCP4.5 from (+0.94°C to +1.68°C) and (+1.61°C to +3.32°C) While Under RCP8.5 that ranges from (+0.91°C to 1.93°C) and (+2.67°C to 4.00 °C) in both future periods of 2030s and 2060s respectively. Monthly minimum temperature increase ranges from (+1.14°C to +2.56°C) and (+1.72°C to +3.74°C) under RCP4.5 scenario while (+1.24°C to +2.21°C) and (+3.02°C to +5.03°C) under RCP8.5 in both future periods 2030s and 2060s respectively. The performance of SWAT model in simulating the stream flow was shown to be good with a coefficient of determination (R2) 0.66 and 0.65 and the Nash and Sutcliffe efficiency (NSE) of 0.65 and 0.62 for calibration and validation periods, respectively. The impacts of climate change on stream flow were assessed by comparing the baseline and future stream flow. The results obtained from this study indicates that the annual streamflow that is projected to decrease by 7.38 % and 33.49% under RCP4.5 in future periods of 2030s and 2060s respectively. For RCP8.5, projected to decrease by 19.44 % and 8.79% by the 2030s and the 2060s, respectively. Results from this study showed that the combined effects of decrease in precipitation and increase in temperature in the future period would decrease stream flow. Hence, it is strictly recommended that the adaptation measures such as watershed based integrated water resource management approach and constructing water harvesting structures to store excess water flowing during rainy season so as to use it for dry season