Babaousmail et al. (2025) 21 st century projections of concurrent hot-dry extremes and population exposure in North Africa under two socioeconomic scenarios

Identification

• Journal: Theoretical and Applied Climatology
• Year: 2025
• Date: 2025-12-29
• Authors: Hassen Babaousmail, Brian Ayugi, Richard Mumo
• DOI: 10.1007/s00704-025-05990-2

Research Groups

• School of Atmospheric Science and Remote Sensing, Wuxi University, Wuxi, China
• Wyss Academy for Nature at the University of Bern, East Africa Hub, Nanyuki, Kenya
• Department of Mathematics and Statistical Sciences, International University of Science and Technology, Palapye, Botswana

Short Summary

This study projects the evolution of compound hot-dry extreme (CHDE) events and associated population exposure in North Africa under two socioeconomic scenarios (SSP2-4.5 and SSP5-8.5), finding a significant increase in CHDE frequency (65–90% under SSP5-8.5) and a tripling of population exposure by 2100, with cities like Tripoli, Fes, and Rabat identified as future hotspots.

Objective

• To investigate the observed and projected variations in compound hot-dry extreme (CHDE) events across the Mediterranean (MED) and Sahara (SAH) regions of North Africa and estimate future human population exposure to these severe events under different socioeconomic pathways.

Study Configuration

• Spatial Scale: North Africa, specifically the Mediterranean region (10° W to 40° E, 30° N to 40° N) and the Sahara region (19° W to 44° E, 14° N to 30° N).
• Temporal Scale:
  • Historical period: 1995–2014
  • Mid-future period: 2041–2070
  • Far-future period: 2081–2100

Methodology and Data

• Models used:
  • Multi-model ensemble (MME) of bias-corrected CMIP6 climate models: EC-Earth-Veg, UKESM1-0-LL, GFDL-CM4, GFDL-ESM4, IPSL-CM6-LR.
  • Shared Socioeconomic Pathways (SSPs): SSP2-4.5 (moderate mitigation) and SSP5-8.5 (high emissions/business-as-usual).
  • Bias correction: Quantile bias correction technique.
  • Interpolation: Bilinear interpolation to 1° x 1° horizontal grid resolution using Climate Data Operator (CDO).
• Data sources:
  • Observational precipitation: Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS v2.0), approximately 111 meters spatial resolution.
  • Observational maximum temperature: CPC Global Unified Temperature, 50 kilometers x 50 kilometers spatial resolution.
  • Population: Gridded Population of the World (GPWv4), 50 kilometers x 50 kilometers resolution, for historical (1995–2014) and future (2015–2100) under SSP2 and SSP5.
  • Methodology: Compound Hot-Dry Extreme (CHDE) events defined using quantile thresholds (moderate: Tmax > 75th percentile and precipitation < 25th percentile; severe: Tmax > 90th percentile and precipitation < 10th percentile). Trends analyzed using Sen slope and modified Mann-Kendall test. Population Exposure (PE) calculated as the product of CHDEs frequency and population.

Main Results

• Historical Trends (1995–2014): Both moderate and severe CHDEs increased across the MED and SAH regions. Severe events were more frequent in major cities like Fes, Casablanca, Djanet, and Nouakchott. Fes experienced a >300% increase in severe CHDEs in 2003, linked to intense wildfires.
• Projected Changes (2015–2100):
  • All CMIP6 models project a statistically significant increase in CHDE frequency under both SSP2-4.5 and SSP5-8.5 scenarios.
  • Under SSP5-8.5, moderate and severe CHDE frequency is projected to rise by 65–90% by 2100.
  • Moderate CHDE events are projected to be up to 2.5 times more frequent in the MED region under SSP5-8.5, especially after 2065. In the SAH region, moderate events increase from 2020, and severe events after 2040.
  • Cities such as Tripoli, Fes, and Rabat are identified as future hotspots, with severe events projected to intensify and become more frequent, potentially surging over 400% in Tripoli after 2095 under SSP5-8.5.
• Population Exposure:
  • Population exposure to CHDEs is projected to triple by 2100 under SSP5-8.5.
  • Moderate events are expected to impact a larger proportion of the population, particularly in the MED region.
  • Cairo is identified as the most at-risk metropolitan area, with exposure potentially exceeding billions of person-days.
  • Multi-year mean population exposure to moderate events in the far future is projected to reach 190 x 10^5 person-days under SSP2-4.5|SSP2 and 160 x 10^5 person-days under SSP5-8.5|SSP5 over the MED region. For the SAH region, it is projected to reach approximately 25 x 10^5 person-days.

Contributions

• First study to quantify the impact of compound hot-dry extremes on the population over the dryland regions of the Mediterranean and Sahara.
• Provides comprehensive observed and projected variations in CHDEs across North Africa using bias-corrected CMIP6 models.
• Identifies specific urban hotspots in North Africa highly vulnerable to future CHDE intensification and associated population exposure.
• Highlights the critical roles of local land-surface processes (soil moisture-temperature coupling) and large-scale circulation anomalies (e.g., Azores High expansion) as drivers of CHDE intensification in the region.

Funding

Not explicitly stated in the provided text, beyond general acknowledgement of data centers.

Citation

@article{Babaousmail202521,
  author = {Babaousmail, Hassen and Ayugi, Brian and Mumo, Richard},
  title = {21 st century projections of concurrent hot-dry extremes and population exposure in North Africa under two socioeconomic scenarios},
  journal = {Theoretical and Applied Climatology},
  year = {2025},
  doi = {10.1007/s00704-025-05990-2},
  url = {https://doi.org/10.1007/s00704-025-05990-2}
}