Ferreiro-Lera et al. (2026) Projected Reorganization of Euro-Mediterranean Bioclimates under Climate Change: Evidence from CMIP6 Multi-model Ensemble

Identification

• Journal: Earth Systems and Environment
• Year: 2026
• Date: 2026-03-27
• Authors: Giovanni-Breogán Ferreiro-Lera, Ángel Penas, Sara del Río
• DOI: 10.1007/s41748-026-01145-z

Research Groups

• Department of Biodiversity and Environmental Management, Faculty of Biological and Environmental Sciences, University of León, Campus de Vegazana s/n. E-24071, León, Spain
• Mountain Livestock Institute (CSIC-ULE), Vega de Infanzones, León-Vega de Infanzones Road (Marzanas-Grulleros), León, 24346, Spain

Short Summary

This study projects future bioclimatic shifts in the Euro-Mediterranean region using a multi-model ensemble of 25 CMIP6 GCMs and two classification systems (Köppen–Geiger and WBCS), revealing a consistent trend towards warmer, more xeric, and continental conditions, with the WBCS providing more nuanced insights into transitional changes.

Objective

• To investigate projected bioclimatic shifts across the Euro-Mediterranean region over short (2026–2050), medium (2051–2075), and long term (2076–2100) under optimistic (SSP1–RCP2.6), intermediate (SSP2–RCP4.5), and pessimistic (SSP5–RCP8.5) emission pathways.
• To establish the relationships between Köppen–Geiger Classification System (KGCS) types and Worldwide Bioclimatic Classification System (WBCS) bioclimates for the Euro-Mediterranean region.
• To assess climatic shifting according to both KGCS and WBCS, hypothesizing that WBCS will show a greater degree of climatic heterogeneity.

Study Configuration

• Spatial Scale: Euro-Mediterranean region, encompassing 18 countries with land area approaching 3,200,000 km², delimited by approximate geographical coordinates 45º E – 35º N – 10º W – 52º N.
• Temporal Scale:
  • Historical reference period: 1981–2010.
  • Future projection periods: Short-term (2026–2050), Medium-term (2051–2075), Long-term (2076–2100).
  • Emission pathways: SSP1–RCP2.6, SSP2–RCP4.5, SSP5–RCP8.5.

Methodology and Data

• Models used:
  • Climate Classification Systems: Köppen–Geiger Classification System (KGCS) and Worldwide Bioclimatic Classification System (WBCS).
  • Ensemble method: Random Forest Multi-model Ensemble (RF-MME).
  • Performance metrics: Heidke Skill Score (HSS), Peirce Skill Score (PSS), Gerrity Score (GS), chi-square (χ²), Comprehensive Rating Index (CRI), and the newly introduced Distance to Randomness (DR) and relative Distance to Randomness (rDR).
• Data sources:
  • General Circulation Models (GCMs): Monthly temperature and rainfall data from 25 CMIP6 GCMs (e.g., ACCESS-ESM1-5, GFDL-ESM4, MRI-ESM2-0) obtained from the Lawrence Livermore National Laboratory ESGF node.
  • Reference dataset: Monthly mean temperature and precipitation from ERA5 Land reanalysis (0.1º spatial resolution) retrieved from the Copernicus Climate Change Service.
  • Data processing: Empirical Bayesian Kriging (EBK) for interpolation and resolution equalization.

Main Results

• ACCESS-ESM1-5, GFDL-ESM4, and MRI-ESM2-0 consistently emerged as the best-performing GCMs for reproducing historical bioclimatic conditions across both classification systems.
• The novel Distance to Randomness (DR) metric effectively assessed GCM performance for individual bioclimatic types, revealing that models with lower overall performance could still accurately detect minority climate types (e.g., Cfc and Et).
• A Random Forest Multi-model Ensemble (RF-MME) incorporating all 25 GCMs demonstrated superior performance and robustness compared to smaller ensembles, benefiting from model diversity.
• Future projections using KGCS indicate a two-phase shift: (i) increasing summer drought (Cf types replaced by Cs types); and (ii) increasing thermicity (warmer "a" subtypes appearing). Under the pessimistic SSP5–RCP8.5 scenario, a significant expansion of arid climates (B types) is projected by the end of the century in southern Iberia, Sardinia, southern Italy, and the Aegean Sea.
• Future projections using WBCS reveal three distinct phases of bioclimatic shifting: (i) mediterraneization, with temperate bioclimates retreating to northern positions (e.g., Alps, Carpathians); (ii) xerification, characterized by an increase in Mediterranean xeric bioclimates replacing pluviseasonal ones; and (iii) continentalization, with an increase in mepc and mexc extension, and the potential appearance of medc in central Spain and Turkey.
• While a tangible correspondence exists between KGCS and WBCS, the WBCS provides more detailed information on bioclimatic shifts, particularly by revealing increased continentality, which is less evident in the KGCS framework.

Contributions

• First comprehensive assessment of projected bioclimatic shifts in the Euro-Mediterranean region using a multi-model ensemble of 25 CMIP6 GCMs, evaluated with both the Köppen–Geiger and Worldwide Bioclimatic Classification Systems.
• Introduction and validation of the "Distance to Randomness (DR)" metric, offering a novel, geometrically explicit interpretation of GCM skill in ROC space for category-specific performance assessment.
• Demonstrated the efficacy of a Random Forest Multi-model Ensemble (RF-MME) in leveraging model diversity for robust projections, even when including lower-performing GCMs.
• Provided a detailed, multi-scenario, and multi-temporal analysis of bioclimatic reorganization, identifying distinct phases of mediterraneization, xerification, and continentalization.
• Established and graphically depicted equivalences and relationships between KGCS climatic types and WBCS bioclimates for the study area.
• Offers a robust and transferable methodological framework for detecting bioclimatic shifts in climate-sensitive regions, with direct implications for biodiversity conservation, ecosystem management, and climate adaptation strategies.

Funding

• Spanish Ministry of Universities, General Secretary of Universities (Government of Spain) (Grant Ref.: FPU21/03022)
• FEDER European Funds
• Junta de Castilla y León under the Research and Innovation Strategy for Smart Specialization (RIS3) of Castilla y León 2021-2027

Citation

@article{FerreiroLera2026Projected,
  author = {Ferreiro-Lera, Giovanni-Breogán and Penas, Ángel and Río, Sara del},
  title = {Projected Reorganization of Euro-Mediterranean Bioclimates under Climate Change: Evidence from CMIP6 Multi-model Ensemble},
  journal = {Earth Systems and Environment},
  year = {2026},
  doi = {10.1007/s41748-026-01145-z},
  url = {https://doi.org/10.1007/s41748-026-01145-z}
}