Abraham et al. (2025) Assessing the Flood and Drought Regulation Capacity of Dams in a Changing Climate: An Application to the Largest Hydropower Dam in Africa

Identification

• Journal: Earth Systems and Environment
• Year: 2025
• Date: 2025-09-30
• Authors: Tesfalem Abraham, Gebre Gelete, Yan Liu
• DOI: 10.1007/s41748-025-00815-8

Research Groups

• Department of Water Resources and Irrigation Engineering, Institute of Technology, Hawassa University, Ethiopia
• Environmental and Atmospheric Sciences Research Group, Scientific Research Center, Al-Ayen University, Iraq
• College of Agricultural and Environmental Science, Arsi University, Ethiopia
• Faculty of Civil and Environmental Engineering, Near East University, Turkey
• Agrosphere (IBG-3), Forschungszentrum Jülich, Germany
• Soil Physics and Land Management Group, Wageningen University and Research, The Netherlands

Short Summary

This study quantifies the Grand Ethiopian Renaissance Dam's (GERD) flood and drought regulation capacity under projected climate change, demonstrating its substantial moderating effect on both extreme hydrological events in the transboundary Upper Blue Nile basin.

Objective

• To investigate how extreme flood events and their frequency are affected by GERD operation.
• To analyze how hydrological drought events and their characteristics change with GERD operation.
• To determine the extent to which climate change alters flood and drought characteristics with and without GERD.

Study Configuration

• Spatial Scale: Upper Blue Nile (UBN) River basin, Ethiopia, covering an area of 176,000 square kilometers, focusing on the Grand Ethiopian Renaissance Dam (GERD).
• Temporal Scale:
  • Historical period: 1981–2005
  • Near-future (NF): 2025–2049
  • Mid-future (MF): 2050–2074
  • Far-future (FF): 2075–2099

Methodology and Data

• Models used:
  • HBV hydrological model (lumped) for streamflow simulation.
  • Coordinated Regional Climate Downscaling Experiment (CORDEX) Regional Climate Models (RCMs): RCA4CNRM, RCA4CSIRO, RCA4GFDL, RCA4MIROC5, and RCA4_NorESM.
  • Scaled distribution mapping technique for bias correction of climate model outputs.
  • Annual Maximum Series (AMS) method for flood frequency analysis.
  • Non-parametric Standardized Streamflow Index (SSI) using the Gringorten plotting position for drought analysis.
• Data sources:
  • Precipitation: Multi-Source Weighted-Ensemble Precipitation (MSWEP v2) for historical period.
  • Potential Evapotranspiration (PET): Calculated using the Hargreaves equation, based on ERA5 temperature data (historical) and climate model temperature data (future).
  • Temperature: ERA5 (historical), CORDEX RCMs (future).
  • Streamflow: Simulated data from Ali et al. (2023) for Eldiem station, used as a proxy for observed data for HBV model calibration and validation.
  • GERD reservoir storage-elevation (S-E) curve: Wheeler et al. (2016).
  • GERD reservoir operation rules: Lazin et al. (2023).

Main Results

• GERD operation significantly moderates both flood and drought conditions across historical and future periods.
• Flood Regulation:
  • In the far-future period, the largest 2-year recurrence interval (RI) flood volume of 12.86 billion cubic meters is regulated by 72%.
  • Peak flood magnitudes are consistently reduced across all periods, with a maximum reduction of 4,572.3 cubic meters per second in the historical period.
  • Flood frequency (number of days above RI thresholds) is substantially reduced; for example, a 13-day event for the 2-year RI is reduced to 4 days in the far future.
  • GERD operation introduces a slight shift in the timing of peak flood occurrences, with a maximum delay of 25 days in the mid-future period.
• Drought Regulation:
  • GERD operation yields a significant reduction in peak drought, achieving a maximum reduction of 40.35% in the mid-future period.
  • Drought duration is completely eliminated (100% reduction) in the historical, mid-future, and far-future periods.
  • Drought severity is significantly reduced, reaching up to 100% reduction in the historical, mid-future, and far-future periods.
  • Drought intensity is notably reduced, with a maximum reduction of 14.21% in the near future.
• The HBV hydrological model achieved a median Kling-Gupta efficiency (KGE) of 0.9 during calibration and 0.85 during validation, using 87 selected parameter sets from 20,000 Monte Carlo samples.

Contributions

• This study is the first to quantify the Grand Ethiopian Renaissance Dam's (GERD) transboundary drought regulation capacity using non-parametric Standardized Streamflow Index (SSI) methods under climate change.
• It provides a comprehensive assessment of GERD's flood and drought regulation capacity by comparing natural and regulated flow scenarios across historical and future climate projections.
• The research quantifies uncertainties arising from both hydrological model parameters (HBV) and Regional Climate Models (RCMs) in the reservoir modeling process.
• It highlights the critical role of large reservoirs as climate change adaptation tools, offering benefits for water-sharing countries in transboundary settings by strengthening resilience to climate change.

Funding

No funding was received for conducting this study.

Citation

@article{Abraham2025Assessing,
  author = {Abraham, Tesfalem and Gelete, Gebre and Liu, Yan},
  title = {Assessing the Flood and Drought Regulation Capacity of Dams in a Changing Climate: An Application to the Largest Hydropower Dam in Africa},
  journal = {Earth Systems and Environment},
  year = {2025},
  doi = {10.1007/s41748-025-00815-8},
  url = {https://doi.org/10.1007/s41748-025-00815-8}
}