Assessing the Flood and Drought Regulation Capacity of Dams in a Changing Climate: An Application to the Largest Hydropower Dam in Africa

Floods and droughts resulting from extreme hydrological events are among the most devastating natural hazards. However, reservoir operations, can significantly alleviate flood and drought effects induced by extreme events. In this study, we quantified the flood and drought regulation capacity of the Grand Ethiopian Renaissance Dam (GERD), the largest dam in Africa. We applied a model parameter confinement strategy from 20,000 Monte Carlo parameter samples. Accordingly, we found 87 reduced parameters sets that are obeying the calibration criteria based on KGE, and relative error. By using these reduced parameter sets alongside climate projections, we simulated future inflows to the dam. Based on these simulations, reservoir operation rules were applied to model outflows through both turbines and the spillway. We conducted analyses under two scenarios: i) without GERD and ii) with GERD operation, to assess the dam’s flood and drought regulation capacity both in historical and future periods. We identified flood characteristics at various recurrence intervals (RI). Additionally, we applied a Standardized Streamflow Index (SSI) to determine hydrological drought and its characteristics. The findings indicate that GERD operation has a substantial regulatory effect on both flood and drought conditions. In the far-future period, the largest 2-year RI flood volume of 12.86 bcm is regulated by 72%. Across all periods, peak flood magnitudes are consistently reduced, with a maximum reduction of 4,572.3 m³/s. Furthermore, GERD’s operation yields a significant reduction in peak drought, achieving a maximum reduction of 40.35% in the mid-future period. Among various drought characteristics, drought intensity is notably reduced by GERD operation, with a maximum reduction of 14.21% in the near future. This study demonstrates the potential of reservoirs for flood and drought regulation as climate change adaptation tools, benefiting water-sharing countries in transboundary settings by strengthening resilience to climate change.