Hydrology of the Blue Nile Basin Overview

Abstract

The Blue Nile (Abay) basin contributes close to 60% of the flow of Nile River while draining only 10% of the Nile Basin. Analysis and study of the past, current and future climate and hydrology of the Blue Nile basin is important to sustain the environment and livelihood in the Nile Basin. The basin mean annual rainfall is 1423 mm with 74% in the four wet months of June to September. Rainfall in the basin is influenced by ENSO events where El Nino years are likely to be drier than normal and La Nina years are likely to be wetter. River flow fluctuates with the timing and amount of rainfall. The estimated mean annual flow of the Blue Nile River at the Ethio-Sudan border is about 50 bcm (billion cubic meter) with range of year-to-year variation. The subsistence rainfed agriculture in the basin has been affected by periodic droughts and may not be sustainable to support the growing population. Increasing water demand in the Nile basin for food and energy is manifested in the continual increase of water control projects on the main rivers and tributaries and expansion of irrigated areas. These projects are likely to alter the hydrology of the Blue Nile Basin. One of the currently undergoing projects is the Grand Ethiopian Renaissance Dam (GERD) being built on the Blue Nile River by Ethiopia for hydroelectric power generation. This chapter provides an overview of the hydrology of the Blue Nile Basin.