Sintayehu Legesse Gebre, Kassa Tadele and Bogale G Mariam
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. The climate changes variables used as input in to HBV hydrological model to simulate the future runoff at the out let of gauging station of Near Arjo town. The impact of climate change on future runoff resulted a positive magnitude change in average runoff flow at the outlet of the catchment. The increase in average runoff is associated with the increase in precipitation projection over the catchment. During the main rainy season of summer, at 2030`s and 2090`s average seasonal runoff percentage change may increase up to+157% and+136% respectively as compared to the base line period. Hence, more likely in the future the water resources availability may increases in the catchment. This may create an opportunity for small scale farmers to harness enough amount of water during rainy season for later use.