EVALUATION OF CLIMATE CHANGE IMPACT ON STREAMFLOW OF GOJEB WATERSHED, OMO GIBE BASIN, ETHIOPIA

Abstract

Understanding future stream flow in watershed is increasingly important for water resource management. The main objective of this study was to assess the possible impacts of future climate change on stream flow in the Gojeb catchment of Omo Gibe River Basin using two greenhouse gas (GHG) emission scenarios; RCP4.5 and RCP8.5.The outputs of three RCMs from the CORDEX were evaluated and bias-corrected for both rainfall and temperature in comparison with observed data before using the output as input for hydrological model. A hydrological model, HEC-HMS was utilized to simulate the stream flow. The model was calibrated and validated at an outlet of the catchment station using observed stream flow data. The performance of the model was resulted with NSE of 0.76 during calibration (1992-2000) and 0.73 during validation (2001-2005) period. The estimated average annual potential ETo in the watershed in near-term (2021-2050) of both emission scenarios projected to increase from 1.03% up to 2.89%, and in mid-term (2051-2080) the average annual potential ETo projected to increase from 2.49% up to 4.50% under both scenarios. In the near-term the average annual rainfall change projected between (-4.02% and +8.10%) under RCP4.5 and (-13.15% and +3.04%) under RCP8.5. Whereas, in mid-term climate models projected between (-2.03% and - 19.96%) under RCP4.5 and (-8.75% and -23.09%) under RCP8.5 emission. The HEC-HMS was used to simulate catchment stream flow for three periods: baseline (1971-2000), near term (2021- 2050) and mid-term (2051- 2080) projections. The stream flow projection shows a decrease from January to August under both emission scenarios in the range of (-1.01 to -17.23%) in near-term and (-3.05% to -33.31%) in mid-term, and also an increase from September to November. These increments are within (>5%) in near-term and mid-term for both emission scenarios. Relative to the baseline period, the change in mean annual stream flow from mid-term (2051-2080) is mostly negative indicates that, the decrease in available discharge in the river under RCP4.5 and RCP8.5 scenarios. This study provides useful information for future water resource planning and management in the face of climate change on the streamflow of Gojeb catchment.