Gebreegziabher et al. (2025) Projected future temperature, precipitation, and drought conditions in the Muger River sub-basin, central Ethiopia, using CMIP6 models

Identification

• Journal: Discover Atmosphere
• Year: 2025
• Date: 2025-11-06
• Authors: Gizaw Abera Gebreegziabher, Sileshi Degefa, Wakgari Furi
• DOI: 10.1007/s44292-025-00051-9

Research Groups

• Center for Environmental Science, Addis Ababa University, Ethiopia

Short Summary

This study projects future temperature, precipitation, and drought conditions in the Muger River watershed, Ethiopia, using bias-corrected CMIP6 models under SSP2-4.5 and SSP5-8.5 scenarios, revealing significant warming, declining precipitation, and intensifying aridity by the end of the century.

Objective

• To evaluate how future changes in temperature and precipitation, under SSP2-4.5 and SSP5-8.5 scenarios, may affect drought dynamics in the Muger River watershed.
• Principal hypothesis: Projected future climate conditions, as simulated by bias-corrected CMIP6 GCMs, will significantly alter temperature regimes, reduce precipitation, and increase the frequency and severity of drought in the Muger River watershed.

Study Configuration

• Spatial Scale: Muger River watershed, central Ethiopia, approximately 731,000 hectares within the Upper Blue Nile River Basin. Data harmonized to a 0.05° (approximately 5 km) resolution.
• Temporal Scale:
  • Baseline period: 1981–2010 (for observations and bias correction), 1985–2014 (for EMI reference).
  • Historical GCM simulations: 1950–2014.
  • Future projection periods: 2015–2100, analyzed for near-term (2021–2040), mid-century (2041–2070), and end-century (2071–2100).
  • Historical drought analysis: 1980–2022.

Methodology and Data

• Models used:
  • Climate Models: Six CMIP6 General Circulation Models (GCMs): CNRM-CM6-1, GFDL-ESM4, CNRM-CM6-1-HR, MIROC6, ACCESS-CM2, MRI-ESM2-0.
  • Bias Correction: CMhyd tool using the quantile mapping (QM) technique.
  • Drought/Climate Extreme Indices: ClimPACT2 software, Google Earth Engine (GEE).
  • Potential Evapotranspiration (PET) Estimation: Thornthwaite method.
• Data sources:
  • Observational Climate Data: Daily gridded precipitation and temperature (minimum and maximum) from the National Meteorological Institute of Ethiopia (NMIE) for 1981–2010 (approximately 4 km resolution). Daily gridded climate observations (1985–2014) from the Ethiopian Meteorological Institute (EMI) as reference.
  • Climate Model Data: CMIP6 GCM outputs for Tmin, Tmax, and precipitation for historical (1950–2014) and future (2015–2100) periods under SSP2-4.5 and SSP5-8.5 scenarios.
  • Other Spatial Data: NDVI, land use/land cover maps, elevation, and soil data (used for harmonization).

Main Results

• Bias Correction Performance: Bias correction significantly improved the alignment of GCM outputs with observed data. For precipitation, Nash–Sutcliffe efficiency (NSE) improved from -0.85–0.88 to 0.95–0.97, and Root Mean Square Error (RMSE) dropped from 1.28–12.55 mm to 0.68–2.01 mm. Temperature RMSE values were reduced to 0.00–0.03 °C for Tmax and 0.01–0.02 °C for Tmin.
• Temperature Projections (by 2100, relative to 1981–2010 baseline):
  • Under SSP2-4.5: Maximum temperature (Tmax) is projected to rise by +3.2 °C (range: +2.4 to +4.5 °C), and minimum temperature (Tmin) by +2.9 °C (range: +2.0 to +4.1 °C).
  • Under SSP5-8.5: Tmax is projected to rise by +6.4 °C (range: +5.2 to +7.7 °C), and Tmin by +4.5 °C (range: +3.3 to +5.6 °C).
  • Monthly temperatures show consistent warming across all months, with peaks in May.
• Precipitation Projections (by 2100, relative to 1981–2010 baseline of 1147.5 mm/year):
  • Under SSP2-4.5: Mean annual precipitation is projected to decline to 825.1 mm/year (range: 600–1254 mm/year), representing a reduction of 322.4 mm/year.
  • Under SSP5-8.5: Mean annual precipitation is projected to decline to 595.8 mm/year (range: 420–890 mm/year), representing a reduction of 551.7 mm/year.
  • Monthly precipitation generally declines, with reductions of up to 48% (SSP2-4.5) and 60% (SSP5-8.5) in the short rainy season, and 32% (SSP2-4.5) and 42% (SSP5-8.5) in the main rainy season.
• Drought Conditions (SPEI-12):
  • Historical (1980–2022): The region experienced extreme droughts (e.g., SPEI-3 of -2.39 in May 1985; SPEI-12 of -2.625 in May 1988), with May consistently identified as the driest month.
  • Future: Increasing drought frequency and severity. Under SSP2-4.5, the frequency of wet years declines from 46% (2020s) to 23% (2080s). Under SSP5-8.5, wet years decline from 40% (2020s) to 16% (2080s), with SPEI-12 values compressing to +0.43 to -1.38 by the 2080s, indicating dominant moderate to severe droughts.
• Climate Extremes (CDD, TX90p, WSDI): Projections indicate an increase in consecutive dry days (CDD > 130 days), frequency of extremely hot days (TX90p > 20%), and extended warm spells (WSDI > 85 days), particularly by the 2080s under the SSP5-8.5 scenario, suggesting an emerging compound climate risk regime.
• Inter-annual Variability: The standard deviation of annual precipitation increases from 156.2 mm (baseline) to 201.9 mm (SSP5-8.5, 2080s), and the coefficient of variation (CV) for precipitation rises from 13.6% to 18.3%, indicating greater climatic instability.

Contributions

• Provides one of the first localized assessments of compound climate extremes in the Muger watershed using high-resolution, bias-corrected CMIP6 data.
• Applies a suite of climate indices rarely used together in this region, offering a comprehensive picture of multi-hazard climate risks.
• Links climate science to policy by supporting climate-resilient infrastructure design and water management in a strategically important but understudied watershed.

Funding

The authors did not receive support from any organization for the submitted work.

Citation

@article{Gebreegziabher2025Projected,
  author = {Gebreegziabher, Gizaw Abera and Degefa, Sileshi and Furi, Wakgari},
  title = {Projected future temperature, precipitation, and drought conditions in the Muger River sub-basin, central Ethiopia, using CMIP6 models},
  journal = {Discover Atmosphere},
  year = {2025},
  doi = {10.1007/s44292-025-00051-9},
  url = {https://doi.org/10.1007/s44292-025-00051-9}
}