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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. However, the threat of Ethiopia withholding water is only occasionally credible, as it requires the reservoirs at the GERD and Egypt’s High Aswan Dam (HAD) to both be unusually low, which we show will rarely occur. We simulate a range of operational policies for the GERD, including an adversarial operation policy, which could reduce annual water releases from the HAD by 2.72 billion cubic metres (annual exceedance probability of 0.02) compared to operations that aim to reduce downstream water shortages. However, such an adversarial policy would reduce annual GERD hydropower generation by 1 TWh, which is equivalent to 7% of the GERD’s annual electricity generation. |
