Elhaddad et al. (2025) Nile basin flow regimes under 21st century climate variability

Identification

• Journal: Communications Earth & Environment
• Year: 2025
• Date: 2025-11-10
• Authors: Hesham Elhaddad, Mohamed Sultan, Eugene Yan, Thanh‐Nhan‐Duc Tran, Hugo E. Torres-Uribe, Hadi Karimi
• DOI: 10.1038/s43247-025-02813-0

Research Groups

• Department of Geological and Environmental Sciences, Western Michigan University, Kalamazoo, MI, USA
• Geodynamics Department, National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo, Egypt
• Environmental Science Division, Argonne National Laboratory, Argonne, IL, USA
• Department of Civil and Environmental Engineering, The University of Virginia, Charlottesville, VA, USA

Short Summary

This study assesses future flood risk in the Nile Basin's downstream countries using a calibrated, climate-driven SWAT+ model forced by bias-corrected CMIP6 models under SSP2-4.5 and SSP5-8.5 scenarios, projecting a significant increase in 100-year peak discharges (63% to 85%) and more frequent extreme floods by the 21st century.

Objective

• To assess future flood risk in downstream Nile Basin countries under 21st-century climate variability, specifically projecting the magnitudes and frequencies of extreme streamflow events under SSP2-4.5 and SSP5-8.5 scenarios.

Study Configuration

• Spatial Scale: Entire Nile Basin (approximately three million square kilometers, spanning eleven countries), with a focus on downstream countries and four key gauging stations (Sennar, Khartoum, Tamaniat, Dongola).
• Temporal Scale:
  • Historical baseline: 1984–2016 (for comparison).
  • Model calibration: January 1984 to December 1991.
  • Model validation: January 1992 to December 1997.
  • Future projections: 2026–2100 (with 2025 as warm-up).
  • Bias correction overlap: 2015–2024.

Methodology and Data

• Models used:
  • Soil and Water Assessment Tool (SWAT+) hydrological model (fully calibrated, basin-wide).
  • QSWAT+ 3.0 plugin (for watershed delineation).
  • RSWAT version 4.01 (for calibration, sensitivity, and uncertainty analysis).
  • Coupled Model Intercomparison Project Phase 6 (CMIP6) General Circulation Models (GCMs) from NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP-CMIP6) dataset (30 models selected, 3 representative models used for forcing).
  • Quantile-Quantile Mapping (QQM) for bias correction.
  • Log-Pearson Type III (LP3) distribution for extreme event analysis (best-fit).
  • Bootstrap method for uncertainty analysis.
• Data sources:
  • Topographic: Shuttle Radar Topography Mission Digital Elevation Model (SRTM 90 m DEM).
  • Land Use: USGS Global Land Cover Characterization (GLCC) dataset.
  • Soil: FAO Global Soil Map.
  • Precipitation: Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) (0.25° spatial resolution, 1981–present).
  • Temperature: Climate Hazards Center InfraRed Temperature with Stations (CHIRTS).
  • Auxiliary Meteorological (relative humidity, wind speed, solar radiation): Climate Forecast System Reanalysis (CFSR) global dataset (0.5° spatial resolution).
  • Streamflow Observations: Monthly records from four gauging stations (Sennar, Khartoum, Tamaniat, Dongola) reported by the Egyptian Ministry of Water Resources and Irrigation.
  • Terrestrial Water Storage (TWS) Observations (supporting evidence): GRACE and GRACE Follow-On (GRACE-FO) satellite data (2002-2024).

Main Results

• Increased Peak Discharges:
  • Under SSP2-4.5, 100-year peak discharges are projected to increase by 63% (from a historical ~14,200 m³/s to ~24,100 m³/s).
  • Under SSP5-8.5, 100-year peak discharges are projected to increase by 85% (from a historical ~14,200 m³/s to exceeding 27,400 m³/s).
• Increased Flood Frequency:
  • The historical 100-year flood (~14,200 m³/s) is projected to occur roughly every 4 years under SSP2-4.5.
  • The historical 100-year flood is projected to occur about every 2.75 years under SSP5-8.5.
  • Extreme floods are projected to occur nearly every decade under high-emission scenarios.
• Quantified Increases in Streamflow Extremes (50th percentile):
  • For SSP2-4.5, streamflow extremes are expected to increase by 49% to 63% for 5- to 200-year return periods.
  • For SSP5-8.5, streamflow extremes are projected to increase by 73% to 85% for 5- to 200-year return periods.
• Consistency with Observations: Projected increases in 21st-century streamflow align with recent GRACE and GRACE-FO observations showing increased terrestrial water storage in the Nile Basin (0.24 cm/yr from 2002-2017, and 2.4 cm/yr from 2018-2024).

Contributions

• Presents the first application of a fully calibrated, climate-driven Soil and Water Assessment Tool (SWAT+) model covering the entire Nile Basin, with a focus on downstream regions, forced by bias-corrected CMIP6 models under SSP2-4.5 and SSP5-8.5 scenarios.
• Provides basin-wide projections of extreme streamflow events, addressing limitations of previous studies focused on individual sub-basins or limited climate model ensembles.
• Introduces an open-source Python framework that automates climate data processing, SWAT+ integration, and extreme event analysis, enhancing reproducibility and broad applicability.
• Offers actionable flood risk information and a framework for regional cooperation and preparedness, supporting coordinated planning and adaptive water management strategies in the Nile Basin.
• Establishes a baseline of naturalized hydrological responses to climate variability, setting a foundation for future integration of anthropogenic drivers such as dam operations and land-use change.

Funding

• National Aeronautics and Space Administration (NASA) Earth Science Division grant (80NSSC244K1155).

Citation

@article{Elhaddad2025Nile,
  author = {Elhaddad, Hesham and Sultan, Mohamed and Yan, Eugene and Tran, Thanh‐Nhan‐Duc and Torres-Uribe, Hugo E. and Karimi, Hadi},
  title = {Nile basin flow regimes under 21st century climate variability},
  journal = {Communications Earth & Environment},
  year = {2025},
  doi = {10.1038/s43247-025-02813-0},
  url = {https://doi.org/10.1038/s43247-025-02813-0}
}