EVALUATION OF CLIMATE CHANGE IMPACTS ON RUNOFF IN THE GIDABO RIVER BASIN: SOUTHERN ETHIOPIA

Abstract

Climate change significantly affects many hydrological systems, which in turn affects the runoff and the flow of rivers. Therefore, the aim of this research was taken as to investigate the impacts of possible future climate change scenarios on the runoff of the catchment area of the Gidabo River. Statistical Downscaling Model version 4.2 was used to downscale the daily precipitation, daily maximum and minimum temperature in the basin of the study area. The large-scale climate variables for the A2a and B2a scenarios obtained from the Hadley Centre Coupled Model version 3 were used. After the calibration of the model and testing of the downscaling procedure, the hydrological model was run for the three future periods: 2011– 2040, 2041–2070, and 2071–2099. The meteorological variables such as, precipitation, minimum and maximum temperature that were downscaled from SDSM were used as input to the SWAT hydrological model which was calibrated (R 2 =0.77) and validated (R 2 =0.81) with historical data to examine the possible impact of climate change in the catchment. The impacts of climate change in the basin were assessed by comparing the baseline and future runoff. The results obtained from this study indicates that there is significant variation in the monthly, seasonal and annual runoff. The climate change impacts might cause a decrease in monthly runoff up to 4.1% in the 2020’s and 2.6% in the 2050, but it increase up to 1.6 % in the 2080s for A2a scenario; and it decrease up to 0.2 % in 2020s and increase up to 0.7 and 1.5 % in 2050s and 2080s respectively for B2a scenario. The SWAT simulation of future average total seasonal runoff shows increasing pattern in the months of February to May and June to September for both A2a and B2a scenarios in all time periods. But during the period of February to May a decreasing pattern of average total seasonal runoff in 2050’s for A2a scenario and increasing patter in 2020’s for B2a scenario was shown. In 2020’s, 2050’and 2080’s the average total annual runoff appears to increase by 3.5% ,3% and 6.8% for A2a and 5 %,5.6% and 5.8% for B2a scenarios respectively.