Should Egypt be afraid of the Grand Ethiopian Renaissance Dam? The consequences of adversarial water policy on the Blue Nile

ABSTRACT Although large dams can provide multiple benefits, they may negatively impact downstream riparians, and could be used to cause harm by withholding water. Concern about deliberately adversarial operation of the Grand Ethiopia Renaissance Dam (GERD) is mounting in Egypt and overshadows the regional negotiations around water resources. We simulate a range of operational policies for the GERD, including an adversarial operation policy, which could reduce annual water releases from the High Aswan Dam (HAD) by 2.72 billion cubic meters (annual exceedance probability of 0.02) compared to operations that seek to reduce downstream water shortages. However, such a policy would reduce annual GERD hydropower generation by 1 TWh, which is equivalent to 7% of the GERD's annual electricity generation. The threat of Ethiopia withholding water is only occasionally credible, as it requires the reservoirs at the GERD and the HAD to both be unusually low, which we show will rarely occur.