Drawing on hydrology, rainfall, and climatic data from the past 25 years, this article investigates the effects of climate change on water resources in the transnational Blue Nile Basin (BNB). The primary focus is on determining the long-term temporal and seasonal changes in the flows of the Blue Nile in Ethiopia at the border to Sudan. This is important because the Blue Nile is the main tributary to the Nile river, the lifeline of both Sudan and Egypt. Therefore, to begin with long-term trends in hydrological time series were detected by means of both parametric and nonparametric techniques. The Soil and Water Assessment Tool (SWAT) model was calibrated using several sub-basins and new high-resolution land use and soil maps. Future climate change impacts were projected using data from the Climate Forecast System Reanalysis (CFSR) of the National Centers for Environmental Predictions based on three different climate change scenarios from the Coupled Model Intercomparison Project (CMIP3). Projected time series were analysed for changes in rainfall and streamflow trends. Climate change scenario modelling suggested that the precipitation will increase from 7% to 48% and that streamflow from the BNB could increase by 21% to 97%. The results provide a basis for evaluating future impacts of climate change on the upper Blue Nile River (Abay River). This is the main river basin contributing to the Nile and a source of water for millions of people in Sudan and Egypt, downstream from Ethiopia. Three models (CCCMA, CNRM, MRI) were applied in this research, within two future time periods (2046–2064 and 2081–2099) and one scenario (A1B). The Abay Basin was divided into seven sub-basins, six of which were used as inlets to the lowest basin at the border to Sudan. The above-mentioned results show that under current climate change scenarios there is a strong seasonal shift to be expected from the present main rainfall season (June to September) to an earlier onset from January to May with less pronounced peaks but longer duration of the rainfall season. This has direct consequences on the streamflow of the Blue Nile, which is connected to the rainfall season and therefore has direct effects on the people living in the sphere of influence of the Nile River.

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This study assesses the interrelationships between terrace development and topographic factors, soil erosion, and soil dislocation by tillage in Minchet Catchment in the Ethiopian Highlands. Data were collected through a mix of modelling soil erosion using the Universal Soil Loss Equation adapted to Ethiopia, and measuring slope and soil deposition above the terraces. The terraces, which developed over 29 years following construction of fanya juu bunds on cropland, reduced the cropland's current slope gradient to half of its original slope, leading to about 39% less soil erosion. Currently, of the total 50 t · ha−1 · yr−1 soil deposition measured above the terraces, about 22 t · ha−1 · yr−1 was soil eroded by water, and the other 28 t · ha−1 · yr−1 was soil that had been dislocated by tillage. This shows that Soil and Water Conservation technologies in the study area are effective in reducing slope gradient and slope length, and thus also in trapping eroded soil, slowing soil movement by tillage, and ultimately, in reducing soil erosion. However, current soil loss from the fields still exceeds the soil formation rate of the study area. We thus highlight possible options to further reduce soil erosion in the crop fields, such as increasing the number of terraces in areas with wider spacing and growing multipurpose and productive grasses and trees on terraces.

To assess the spatial and temporal availability of blue and green water for up- and downstream stakeholders, the hydrological responses of the upper Blue Nile basin in the Ethiopian Highlands was modelled and analysed with newly generated input data, such as soil and land use maps. To consider variations in the seasonal climate, topography, soil, land use, and land management, the upper Blue Nile basin was modelled in seven major sub-basins. The modelling showed significant spatial and temporal differences in the hydrological responses of different sub-basins and years. The long-term mean annual drainage ratios of the watersheds range from <0.1 to >0.65, and the annual drainage ratio of one sub-basin can vary from 0.22 to 0.49. Steep slopes, shallow soils, and cultivated areas increase the drainage ratios due to high surface runoff, low soil moisture content, and a smaller share of evapotranspiration. Various climate change scenarios predict more precipitation, and land use change scenarios foresee a higher share of cultivated areas due to population growth. In view of these trends, results from our study suggest that drainage ratios will increase and more available blue water can be expected for downstream stakeholders.