Predictions of the impacts of climate change on the intensity, amount, and spatial and temporal variability of rainfall and temperature are required. The aim of this study was to assess the status of climate change and hydrological response to climate change for Gumara River sub-basin. Statistical Downscaling Model (SDSM 4.2) was used to downscale HadCM3A2a and HadCM3B2a predictors into finer scale resolution. To estimate the level of impact of climate change, climate change scenarios of precipitation and temperature were divided into four time windows of 25 years each from 2001 to 2099. The Soil and Water Assessment Tool (SWAT) was used to simulate the hydrological response. The results showed that the SWAT calibration and validation reveals a good agreement with R2 = 0.9 and NSE = 0.89 during calibration and R2 = 0.89 and NSE = 0.86 during validation. Annually, both precipitation and temperature showed increasing trends in all future time horizons in which precipitation increases up to a maximum of 13.7% (2076 to 2099) and temperature increases by 1.010c (2076 to 2099). The change in average flow volume due to climate change mainly corresponds to the change in precipitation. The average annual flow volume for the future increases by 17.8% (2076 to 2099). Overall, it appears that climate change will result in an annual increase in flow volume for the Gumara River. The increase in flow is likely to have considerable importance for local small scale irrigation activities. Since the flow volume increases in small rainy season (Belg) and main rainy season (Kiremit), due attention is also needed to prevent flood hazards. Generally, results presented in this study can provide valuable insight to decision makers on the degree of vulnerability of Lake Tana Basin to climate change, which is important to design appropriate adaptation and mitigation strategies.
Key words: Gumara river, climate change, SDSM, SWAT model.
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