Evaluation of Climate Change Impact on Hydrology (A Case Study of Upper Abay Basin) Using CORDEX-RCP Climate Data and SWAT Model

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Climate change is becoming one of the most arguable and threatening issues in terms of global context and their socio/economic driver. This study aims to assess the Annual, seasonal, monthly and extreme Discharge trend of Abay River at Kesse Gauging station by creating Hydrological response model under changing rainfall and temperature using data from an ensemble of downscaled climate data based on the Coordinated Regional climate Downscaling Experiment over African domain (CORDEX-Africa) with Coupled Model Inter-comparison Project Phase 5 (CMIP5) simulations under Representative Concentration Pathway‟s viz. RCP2.6, RCP4.5 and RCP8.5 climate scenarios. Observed climate data from different stations within the Upper Abay basin were collected, Bias correction was performed for the RCP climate data (temperature and rainfall data), soil and water assessment Tool (SWAT) was calibrated and validated for stream flow simulation using SWAT-CUP with a method of SUFI2.The performance of the model was assessed through calibration and validation process and resulted R = 0.76 and E NS 2 = 0.91and E NS = 0.74 during validation for monthly base simulation and R = 0.9 during calibration and R 2 = 0.81 during calibration R 2 = 0.72, E NS = 0.69 for daily base simulation The future projection period were divided in to three viz. 2030s (2031–2040), 2050s (2051– 2060, and 2090s (2091–2100) and compared with the historical or base period (2001–2010) to explore the changes in Precipitation, Potential evapotranspiration and stream flow. From the results obtained, the mean monthly, seasonal and annual rainfall and Potential evaporation is expected to increase in all the future time series for all RCP scenarios. The projected annual mean precipitation and Potential Evaporation shows an increasing trend from the base period by (+9.4%), (+14.6%) and (+20.7%) for precipitation and by (+3.8%), (+3.9%) and (+3.6%) for potential evaporation during 2030s, 2050s and 2090s respectively under RCP2.6.For RCP4.5 the projected annual mean precipitation shows an increase by (+9.9%), (+15.6%) and (+25.2%) and potential evaporation by (+4.8%), (+6%) and (+6.6%) during 2030s, 2050,and 2090s respectively. The change in magnitude for RCP8.5 shows an increasing trend for precipitation with (+18.1%), (+23.4%) and (+36.6%) and potential evaporation by (+4.3%), (+8.5%) and (+18.2%) during 2030s, 2050, and 2090s respectively. The projected stream flow for mean monthly, seasonal and annual flows shows an increasing trend when compared to the base period. Stream flow is expected to increase in the future, at 2030s average annual stream flow projection change may increase by (+7.8%) for RCP2.6, (+11.1%) for RCP4.5 and (+15.28%) for RCP 8.5 scenarios. At 2050s the corresponding average annual stream flow percentage changes increase by (+11.7%) for RCP 2.6, (+14.5%) for RCP4.5 and (+23.64%) for RCP8.5 scenarios. At 2090s average annual Stream flow projection change may increase up to (+22.0%) for RCP2.6, +24.5% for RCP4.5 and +41.24% for RCP8.5 scenarios. The seasonal flow pattern also shows an increasing trend from the base period with maximum increment in Belg by (+62.6%) and Bega by (+33.1%) and Kiremt by (+12.9%) for RCP2.6 i n 2090s. For RCP4.5 the maximum increase in stream flow shows (+40.9%) for Belg, (+30.7) for Bega and (+20.3%) for Kiremt season in 2090s. For RCP8.5 the maximum change in seasonal stream flow shows (+66.6%) for Belg, and (+70.8%) and (+29%) in 2090s. Annual Peak flow pattern shows an increasing trend in all future time series under all RCP scenarios except for RCP2.6 with (-1.4%) decrease in2036.Max increase by (+26.7%) for RCP2.6 in 2095, (+24%) for RCP4.5 in2095 and (+30.8%) for RCP 8.5 in 2092. But the annual low flow pattern shows both an increasing and decreasing trend in the future with maximum increase (+145.7%) in 2092 and maximum decrease (-54%) in 2056 for RCP2.6, for RCP4.5 maximum increase (+155.5%) in 2093 and maximum decrease (-36.4%) in 2034 is observed. For RCP8.5 maximum increase (+281.2%) in 2094 and maximum decrease (-33.5%) in 2037 is observed. From this study, it was concluded that the changing climate cloud have an impact on the availability of water and the increased in flow volume in the basin cloud be useful for water resources management and policy making so that climate change cloud be incorporated in the plans and management of future and existing water resource projects in the basin.



Upper Abay basin, Climate Change, CORDEX-Africa, CMIP5, RCP, SWAT, Scenario, SWAT-CUP, SUFI2