Climate changes alter regional hydrologic conditions and results in a variety of impacts on waterrnresource systems. Such hydrologic changes will affect almost every aspect of human well-being.rnThe goal of this thesis is to assess the impact of climate change on the hydrology of Upper Guderrncatchment located in Northwest of Ethiopia. The GCM derived scenarios (HadCM3 A2a & B2arnSRES emission scenarios) experiments were used for the climate projection. The statisticalrnDownscaling Model (SDSM) was used to generate future possible local meteorological variablesrnin the study area. The down-scaled data were then used as input to the Soil and Water AssessmentrnTool (SWAT) model to simulate the corresponding future stream flow regime in Upper Guderrncatchment of the Abbay River Basin. A semi distributed hydrological model, SWAT wasrndeveloped and Generalized Likelihood Uncertainty Estimation (GLUE) was utilized forrnuncertainty analysis. GLUE is linked with SWAT in the Calibration and Uncertainty Programrnknown as SWAT-CUP.rnThree benchmark periods simulated for this study were 2020s, 2050s and 2080s. The time seriesrngenerated by GCM of HadCM3 A2a and B2a and Statistical Downscaling Model (SDSM) indicaterna significant increasing trend in maximum and minimum temperature values and a slightrnincreasing trend in precipitation for both A2a and B2a emission scenarios in both Gedo and TikurrnInch stations for all three bench mark periods. The hydrologic impact analysis made with therndownscaled temperature and precipitation time series as input to the hydrological model SWATrnsuggested for both A2a and B2a emission scenarios. The model output shows that there may be anrnannual increase in flow volume up to 35% for both emission scenarios in three benchmark periodsrnin the future. All seasons show an increase in flow volume for both A2a and B2a emissionrnscenarios for all time horizons. Potential evapotranspiration in the catchment also will increasernannually on average 3 - 15% for the 2020s and 7-25% for the 2050s and 2080s for both A2a andrnB2a emissions scenarios.rnKey words: Climate Change; Guder Sub-Basin; GCM; SDSM; SWAT; SWAT-CUP; GLUE