EVALUATION OF IMPACT OF CLIMATE CHANGE ON WATER RESOURCE AVAILABILITY OF ABAYA - CHAMO BASIN: (A CASE STUDY OF KULFO CATCHMENT),ETHIOPIA

Abstract

Nowadays the sign of climate change and its impact is revealing on different natural and man-made systems, in one or other ways. Accordingly, this impact is significant on the water resource system. This study mainly deals with evaluation of the climate change impacts on the Kulfo catchment which is found in Rift valley. Statistical Down Scaling Method was applied in order to downscale the climate variables at catchment level. SDSM was also used to downscale the present and future monthly precipitation and temperature from the UK Hadley center (HadCM3). Two future emission scenarios, A2 and B2 were considered for the three different periods 2030s (2020-2049), 2060s (2050-2079) and 2090s (2080-2099). Downscaling was done to obtain finer resolution output from the GCM, so that it matches with the Kulfo catchment scale. The downscaled future climate showed that the mean daily minimum and maximum temperature increase may up to 1.65/2.0 (2030s), 1.66/3.0 (2060s) and 1.66/3.6 (2090s) and an increase of rainfall with change of 2% (2030s) 6% (2060s) and 11% (2080-2099) for A2 scenario with respect to the baseline period and 1% (2030s), 4% (2060s) and 9 %( 2090s) for B2 scenario. The output of downscaled data provided input rainfall and temperature data for the HEC-HMS model to estimate flow. A hydrological model, HEC-HMS was utilized to simulate the flow. The performance of the model was assessed through calibration and validation process and resulted R 2 =0.86 and NSE=0.85 during calibration and R 2 =0.85, NSE =0.79 during validation. The generated flow to Sikela gauge shows an average annual increase by 24.9% in 2050s (2043-2052) and 26.3% in 2090s (2090-2099) under A2 scenario. The B2 emission scenario projects that the average annual flow volume will increase by 20.9% in 2050s (2043-2052) and 26.11% in 2090s (2090- 2099).The increasing of seasonal mean flow in Bega (JFD) has its own contribution for occurrence of flooding in Kulfo Catchment. It is observed that there may be a net annual increase in mean annual flow volume in Kulfo River due to climate change.