IMPACT OF CLIMATE CHANGE ON WATER AVAILABILITY IN GENALE RIVER SUB-BASIN, SOUTHEASTERN ETHIOPIA

Abstract

Climate change is one of the biggest challenges of the 21stcentury. Since the third assessment report there have been many studies related to trends in river flows during the 20th century at scales ranging from catchment to global. Some of these studies have detected significant trends in some indicators of river flow, and some have demonstrated statistically significant links with trends in temperature or precipitation; but no globally homogeneous trend has been reported. This study examined the trends of climate change and assess impact of future climate change on water resource availability in the Genale river basin Ethiopia using the SWAT model. Climate scenarios project increases in air temperature and decreases precipitation in Genale sub basin during the 2035s and 2065s and these will results in changes of water resource availability. The model was first evaluated using observed climate as input. The coefficient of determination (R2) and Nash-Sutcliffe efficiency (NSE) had been used for calibration and validation period as performance evaluation criteria. The simulation results shows that the SWAT model has good performance for simulating Genale river sub-basin, with R2= 0.86 and NSE = 0.68 for calibration period and R2=0.88 and NSE = 0.73 for validation period. The maximum and minimum temperature trend analysis shows increasing whereas rainfall trend shows statistically insignificant for baseline and future periods. The ensemble RCM CORDEX-Africa was biascorrected and used for two (medium and high) emission RCP storylines. The SWAT model used bias corrected RCP4.5 and RCP8.5 as input to predict the two time slices for climate change impact on water availability of the basin. Both the RCP4.5 and RCP8.5 simulation results indicated the likely reduction of water resources in 2035s (2021 to 2050) and 2065s (2051 to 2080) as compared to the baseline in 2000s (1985 to 2015). The water resources reduction will be likely -33.42% and -32.69% in 2035s and 2065s for RCP4.5 scenario and for RCP8.5 scenario, it will be likely reduced by -14.01% and -52.98% in 2035s and 2065s respectively. Therefore, the current situation of water shortage will likely keep continue for the future in the Genale river subbasin.