EVALUATION OF SURFACE WATER RESOURCE AVAILABILITY UNDER CHANGING CLIMATE CONDITION: CASE STUDY OF GAUGED CATCHMENT IN JEMMA SUB BASIN

Abstract

The sign of climate change and its impact is revealing on different water resource system. The present study was conducted to understand the climate change impacts on surface water availability of Robigumer and Beressa River catchments in Jemma sub basin in Abbay Basin. The Soil and Water Assessment Tool (SWAT) model was applied to study the current (1984- 2008) and future scenarios (2026-2100) runoff magnitude in the catchments and associated uncertainty with the simulated outputs. The model was calibrated for the period of 1984 to 2000 and validated for the period of 2001-2008. The flow parameters that significantly limit the runoff in the catchment and the model uncertainty were assessed using SUFI2 in SWAT– CUP, Cn2, Esco, Canmx and Cn2, Esco and Blai, were the most significant parameter in Beressa and Robigumer catchment respectively. In the end, the future climate change impact studies on water availability of the catchments were done based on the outputs of the Regional Climate Model, A1B emission scenarios. In terms of hydrological model performance the model efficiency magnitude for Beressa and Robigumer catchment is ENS (0.69, 0.75) and R 2 (0.78, 0.79) during calibration and ENS (0.68, 0.62) and R 2 (0.69, 0.63) during validation period respectively, which resulted in moderately good model performance while simulating flow parameters in the catchments. It was also shown from the model uncertainty analysis that the percentage of the simulated data within the uncertainty bound is 78 % for Beressa and 73 % for Robigumer River which are good representation of both catchments. The evaluation of surface water resource availability flow forecasting was done for short term (2026-2050), medium term (2051-2075) and long term (2076-2100) future scenarios. The annual flow volume in Beressa River increased by 47.8% and 54.5% in medium and long term future scenarios respectively and decreased by -61.38% in the short term. Robigumer river flow volume showed annual flow volume increases by 13.5% and 4.7% in the medium and long term period respectively, and decrease by -24.4% for the short term period. The increase in flow volume will have a paramount importance for agricultura l activities practiced by local farmers; therefore any effect on this river is reflected the decrease in flow will directly affect the ongoing water resource developments planned and socio economic development on the area.