Impacts of the Grand Ethiopian Renaissance Dam on the Nile River’s downstream reservoirs

Abstract

The Nile River Basin’s (NRB’s) water resources are vulnerable to hydrologic alteration projects. Construction of the Grand Ethiopian Renaissance Dam (GERD), a hydroelectric power project on the Blue Nile, is expected to improve living standards in Ethiopia and contribute to the country's sustainable development. However, the effects of the GERD on water resources of downstream countries (Sudan and Egypt) have been a source of concern. In this study, eight types of remote sensing data and products were used to assess the impacts of the GERD reservoir’s filling process on Ethiopia’s, Sudan’s, and Egypt’s surface water resources. Specifically, spatiotemporal variability in surface area, volume, rainfall, and water storage for five reservoirs located in Ethiopia (GERD), Sudan (Roseires and Merowe), and Egypt (Lake Nasser and Toshka) for the period 2013–2022 were examined. Results indicate that (1) the GERD reservoir’s three filling phases started in July 2020, July 2021, and August 2022, respectively, (2) at the onset of these three phases, the GERD reservoir covered an area (volume) of 110 ± 7 km2 (1.87 ± 0.07 km3), 233 ± 31 km2 (4.30 ± 0.48 km3), and 544 ± 126 km2 (11.79 ± 2.18 km3), respectively, (3) a reduction in the GERD reservoir’s area (24–49 %) observed at the end of the first two fillings is attributed to enhanced infiltration and evaporation rates at the GERD site, (4) no significant changes were observed in the Roseires and Merowe reservoir’s surface areas, although both Nasser and Toshka reservoirs saw a slight increase in surface area during the investigated period, (5) the observed increase in water storage over the five reservoirs is attributed mainly to increased rainfall rates (6–10 %) and heavy flooding during the GERD filling period, and (6) if the GERD filling continues at the similar rates for an additional four years during drought periods, Egypt's Nile water allocation might be reduced by 35.47 ± 2.29 % (16.57 ± 1.07 km3), which could translate into an agricultural land loss of 33.14 ± 1.81 % each year. This study emphasizes the critical need for Ethiopia, Sudan, and Egypt to work together to effectively and equitably manage the water resources of the NRB.