Future Climate change scenarios of precipitation and potential evaporation were developed using output of dynamically downscaled data of ECHAM5 (GCM) under A1B emission scenario condition for 2030?s (2031-2040) and 2090?s (2091-2100). The projected climate variable showed an increasing trend from the 1991-2000(base period) level. The monthly mean minimum and maximum temperature shows an increasing trend. It is estimated that the average seasonal and annual potential evaporation in the watershed for 2030?s might increase up to 5.2% and 4% respectively and in 2090?s the average potential evaporation might increase up to 15.85% seasonally and 12.66% annually. Besides, at 2030?s it is exhibited that the average seasonal precipitation might increase from 12.14% up to 62.79% and annually 30.22%. The simulation results obtained from the investigation indicated that there was a significant variation in the seasonal and monthly flow in both future period scenarios. Hence, in Didessa watershed, runoff is likely to increase in the future.