This study was carried out in Didessa catchment, which is situated in the south-west part of Blue Nile River Basin. This part of the basin is very important due to the location of the place where different water resources development are undertaking, like the Grand Renaissance dam and other development projects, So it was crucial to study and evaluate the potential impacts of climate change on the hydrology and water resources availability. Future Climate change scenarios of precipitation, temperature and potential evaporation were developed using output of dynamically downscaled data of ECHAM5 (GCM) 50 Kms resolution under A1B emission scenario for 2030’s (2031-2040) and 2090’s (2091-2100). The future projection of the GCM model of climate variables showed an increasing trend as compared to the base line period (1991-2000). At 2030`s and 2090`s average annual precipitation may increases by +33.22% and+8.40% respectively over the Didessa catchment.