Evaluation Of Climate Change Impacts On Stream Flow Of Modjo River Watershed In The Upper Awash River Basin, Ethiopia

Abstract

The concern of Water resources and climate change is escalating to global significance due to high spatiotemporal hydro-climatic variability, which is leading to major challenges of so cio-economic development and sustainability. Climate change and its variability are predict able to elicit change in temperature and precipitation series of streamflow of a watershed. The objective of this study is to assess the Impact of Climate Change on streamflow of Modjo river watershed by using SWAT hydrological models. Statistical downscaling Method (SDSM) applied in order to downscale the climate variables at watershed level to downscale the present and future monthly precipitation and temperature from the Canadian center for climate modeling and Analysis (CanESM2). Two future emission scenarios, RCP 4.5 and RCP 8.5 were considered for the three different periods (2020s, 2050s and 2080). Sequential uncertainty Fittings (SUFI_2) calibration process built in SWAT calibration and uncertainty program (SWAT-CUP) calibrated by 1990 to 2008 and validated by 2009 to 2017 flow data. The performance of the model was evaluated through sensitivity analysis, calibration and validation. The output of downscaled data provides input of rainfall and temperature data for the SWAT model to estimate flow. The result revealed that mean T-max is increasing by 1.54°C and 1.44°C under RCP 8.5 RCP4.5 while; mean daily T-min is increasing by 3.27°C and 1.99°C under RCP 8.5 RCP 4.5 respectively. Similarly, annual precipitation also expected to increase up to 2%, 4% and 7% for RCP 4.5 and 2%, 5% and 9% for RCP 8.5 for 2020s, 2050s, and 2080s respectively. The coefficient of determination (R²), Nash-Sutcliffe Efficiency (NSE), percent Bias and RSR value for the daily streamflow by using SUFI 2 optimization technique was obtained for calibration period 0.87, 0.83,16.4 and 0.41 and for validation period 0.93,0.87,23.1 and 0.29. Simulation of climate change effects on streamflow was increased due to the increment of PCP. The streamflow increased by 4.72m3/s, 4.84m3/s, and 5.38m3 /s for Rcp 4.5 while for RCP 8.5 increased to 3.82m3/s, 3.86m3/s, 3.32m 3/s for the period of Near (2020), Mid (2050) and Far (2080) respectively. This will exceeds the av erage flow of the Modjo watershed. Climate change and its variability will trigger the change in temperature and precipitation series, which will affect streamflow patterns, and volume of watershed. Thus, furthermore significantly predictable effect on socio-economic development. Since, T-Max, T-Min and PCP increasing in all scenarios the impact on Koka reservoir, crop production sustainability and others will increase. Thus, application of inte grated watershed management strategy for Modjo river watershed to optimize water re sources management and option to improve streamflow is vital for the study area.