Assessing Climate Change Impact on Gilgel Abbay and Gumara Watershed Hydrology, the Upper Blue Nile Basin, Ethiopia

Climate change and variability have significant influences on hydrological cycles and the availability of water in the Horn of Africa. Projections of six General Circulation Models (GCMs) in association with high (A2) and low (B1) emission scenarios were adopted in this study from the Special Report on Emission Scenarios (SRES) for the period 2020 - 2039 to assess the impacts of climate changes on the Gilgel Abbay and Gumara watershed hydrology, the upper Blue Nile basin, Ethiopia. The GCMs selected were screened in accordance with baseline climate statistics of study areas. A weather generator was employed to generate daily temperature and precipitation to drive the General Water Loading Function (GWLF) hydrological model for simulating runoffs. Projected changes in temperature differences and precipitation ratios relative to the baseline were analyzed to explain the variations in evapotranspiration and the influences on runoff. Despite the fact that the projected magnitude varies among GCMs, increasing runoff in both wet and dry seasons was observed for both watersheds, attributable mainly to the increase in precipitation projected by most GCMs. In contrast to the great increases in runoff, variations in evapotranspiration are less significant. The projected runoff in both watersheds implies increased potential for promoting agricultural irrigation in the dry season. Furthermore, it would allow greater inflow to Lake Tana, the largest contributor to the Ethiopian Renaissance Dam on the Blue Nile. Therefore, concerned local, state, and federal government organizations shall be prepared to harness opportunities from the projected increase in runoff.