Evaluation of Potential Hydrology and Water Resources Availability Catchment, Blue Nile River Basin, Ethiopia. Evaluation of Potential Impacts of Climate Change on the nd Water Resources Availability Catchment, Blue Nile River Basin, Ethiopia. Impacts of Climate Change on the nd Water Resources Availability of Didessa

Abstract

The study carried out in Didessa watershed, one of the largest tributary of Blue Nile River in terms of volume of water, which is situated in the south-west part of Abay river basin. Due to its great importance of the basin by many criteria, so it was crucial to undertake a research to evaluate the potential impacts of climate change on the water resources availability. In this study because of lack of availability of data it is difficult to consider the whole catchment, only the upper Didessa catchment is considered for the study which wastaking the outlet gauging station at near Arjo town (9981km 2 ).Future Climate change scenarios of precipitation and potential evaporation were developed using output of dynamically downscaled of ECHAM5 (GCM) under A1B emission scenario condition at 2020’s (2031-2040) and at 2080’s (2091-2100).The projected future climate variable showed an increasing trend from the 1991-2000(base period) level. It is estimated that the average seasonal and annual potential evaporation in the watershed at 2020’s might increase up to 5.2% and 4% respectively and in 2080’s the average potential evaporation might increase up to 15.85% seasonally and 12.66% annually. Besides, at 2020’s it is exhibited that the average seasonal precipitation might increase from 12.14% up to 62.79% and annually 30.22% .The maximum increment is observed during spring whilethe minimum in autumn. In the other time horizon, in 2080’s the average seasonal precipitation might vary from -10.29% up to 25.29%, maximum increase in autumnwhere as the only reduction is observed during springseason. These changes of climate variables were used as input to the HBV hydrological model which was calibrated (R 2 =0.601) and validated (R 2 =0.61) with historical data to investigate the potential impacts of climate changes in the catchment. 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. At 2020’s seasonally as well as monthly positive incremental change is observed, during the main rainy season (summer) the percentage changes might reaches up to 157%.At 2080’s the average monthly flow only during the month of April showed 12% reduction, in the rest of the months a great increment is exhibited, the average seasonal flow also showeda significant increment during summer, 136% in respect to the base period. Hence, in Didessa watershed, runoff is likely to increase in the future.