Browsing by Author "Belay, Haileyesus"

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    Evaluation of Climate Change impacts on hydrology on selected catchments of Abbay Basin
    (Addis Ababa University, 2011-06) Belay, Haileyesus; Ayalew, Semu(PhD)
    The purpose of this study was to understand the climate change impacts on Abbay Basin located in Northwest of Ethiopia, using the RegCM3 Regional Climate Model. The RegCM3 model nested with the ECHAM5 General Circulation Model (GCM) were applied. Statistical Down Scaling Method (SDSM) is applied in order to downscale the climate variables at catchment level. A hydrological model, HBV-96 was utilized to simulate the water balance. In terms of hydrological modeling performance, R2 criteria, the 10 catchments gave generally in the range between 0.60 and 0.81 in calibration and in validation between 0.54 and 0.75, which is good representation of the catchments. The projected future climate variables has two future time series, the first future time series (2031-2040) and the second future time series (2091-2100), for both future time series an increasing trend of potential evapotranspiration in all selected watersheds of Abbay basin is observed and the annual percentage change of PET with respect to the base period (1991-2000) has range between +2.78% and +18.98% at Anger and Beles catchments respectively. For the case of precipitation it doesn‘t manifest a systematic increasing or decreasing trend in the future time series. The annual rainfall change with respect to the base period has the range between -3.36% and +2.95% at Beles and Chacha watersheds respectively. The seasonal average runoff will reduce in most of the watersheds and it increase in some watersheds like Anger (+5.5%), Beles (+7.05%), Birr (+17.1%), Koga (+7.92%) and Teme (+2.94%) in the next future time series (2091-2100), the annual percentage change of runoff shows reduction in most of the watersheds between -0.59% (Koga) and -7.78%( Chacha) but only Anger (+7.25%), Neshi (+3.1%) and Teme (+3.86) watersheds show increment. The sensitivity analysis has shown that Watersheds like Anger, Beles, Birr, Guder, Neshi, Muger are more sensitive to rainfall change relative to the other watersheds, and Chacha, Koga, Sechi, Teme, are more sensitive to potential evapotranspiration. Based on the checking of uncertainty almost in all watersheds the generated runoff for the future time series is placed out of the two bounds (5% and 95% probability flow), this implies that the change of percent of generated runoff is not because of hydrologic modeling (uncertainty because of hydrologic modeling is less significant). Keywords: RegCM3, ECHAM5, GCM, SDSM, HBV-96, Watershed, uncertainty