Key messages

The River Nile is extremely sensitive to changes in precipitation with variations impacting lake levels and river discharges. Increases in temperature can also affect the rates of evaporation and evapotranspiration influencing the water balance of the basin. Given the centrality of the fresh water resources to economic and social development of the Nile basin region, it is important to have a good understanding of these variables.

The historical flow records of the Main Nile river clearly highlight the significance of the natural variability of the upper basin for an efficient management of the water resources in the downstream regions. The analysis using the water balances of sub-basins shows that these changes can be explained by the minor changes in rainfall and evaporation.

Although both the Equatorial lakes region and the Blue Nile region are sensitive to changes in the climate, the flows in the Main Nile is mainly controlled by climate changes in the Ethiopian highlands. This is because any change in the runoff in the Equatorial lake area will be completely dampened by the marshes in southern Sudan, the Sudd area.

Apart from the Blue Nile the inflow changes are determined by changes in River Atbara. This river has a comparable setting as the Blue Nile and the sensitivity of the outflow can be assumed comparable to that of the Blue Nile.

Analysis of observed precipitation, evaporation and outflow, reveals that rainfall and evaporation in the equatorial lakes region are large terms compared to the outflow. This means that small changes in rainfall or evaporation easily lead to large changes in outflow of the lake.