Savary et al. (2026) Linking European droughts to year-round weather regimes

Identification

• Journal: Weather and Climate Dynamics
• Year: 2026
• Authors: Onaïa Savary, Constantin Ardilouze, Julien Cattiaux
• DOI: 10.5194/wcd-7-223-2026

Research Groups

• Centre National de Recherches Météorologiques (CNRM), Météo-France
• Centre National de la Recherche Scientifique (CNRS)
• Université de Toulouse

Short Summary

This study investigates the relationship between North Atlantic weather regimes and European meteorological droughts using a year-round framework. It finds that while atmospheric circulation frequency anomalies significantly drive droughts in Western Europe and during winter, their influence is reduced in Eastern Europe and during summer months.

Objective

• To evaluate the causal relationship between large-scale North Atlantic atmospheric circulation patterns (weather regimes) and the occurrence and spatial distribution of seasonal meteorological droughts across Europe throughout the entire year.

Study Configuration

• Spatial Scale: European domain (10° W to 60° E, 30° to 72° N) and the North Atlantic sector (75° W to 64° E, 28° to 75° N).
• Temporal Scale: 1960–2022 (62 years) using daily data from the ERA5 reanalysis.

Methodology and Data

• Models used: ERA5 reanalysis (hourly data aggregated to daily).
• Data sources: 500 hPa geopotential height ($zg_{500}$) for circulation and daily mean precipitation for drought analysis.
• Drought Index: Standardized Precipitation Index with a 3-month integration period (SPI3); droughts defined by a threshold of -0.84 (5-year return period).
• Weather Regimes (WR): Seven year-round regimes identified via k-means clustering of $zg_{500}$ anomalies: Zonal (ZO), Greenland Blocking (GBL), European Blocking (EuBL), Atlantic Ridge (AR), Atlantic Trough (AT), Mediterranean Trough (MTr), and Scandinavian Blocking (ScBL).
• Regionalization: Europe was divided into six sub-regions (Western Europe, Western Mediterranean, Scandinavia, Central Europe, Eastern Europe, and Eastern Mediterranean) using the UPGMA algorithm based on drought synchronicity (Jaccard distance).

Main Results

• Regional Sensitivity: Weather regime frequency anomalies explain approximately 50% of drought events in Western Europe, but only 13.0% to 17.8% in Eastern Europe and the Eastern Mediterranean.
• Seasonal Contrast: The influence of large-scale circulation is significantly higher for winter and autumn droughts compared to summer droughts, where local thermodynamic processes and convection dominate precipitation variability.
• Driver Decomposition: Precipitation deficits are driven by three factors: anomalies in regime frequency ($\Delta fk Ck$), departures from canonical precipitation patterns within a regime ($fk \Delta Ck$), and their interaction. On average, departures from canonical patterns ($fk \Delta Ck$) contribute more to drought than simple frequency shifts.
• Regime Stability: Year-round weather regimes exhibit relatively stable precipitation signatures across seasons, though intensity varies (e.g., the Zonal regime shows stronger precipitation contrasts in winter).

Contributions

• Methodological Innovation: Overcomes the constraints of traditional seasonal weather regime classifications by using a year-round framework, allowing for the analysis of droughts during transitional seasons.
• Regionalized Framework: Provides a data-driven regionalization of Europe based on drought synchronicity rather than arbitrary geographical boundaries.
• Predictive Insights: Highlights the potential for sub-seasonal to seasonal (S2S) drought forecasting by identifying which regions and seasons are most tightly coupled to predictable large-scale circulation patterns.

Funding

• Météo-France
• Centre National de la Recherche Scientifique (CNRS)
• Université de Toulouse
• (Specific project reference codes were not explicitly listed in the provided text).

Citation

@article{Savary2026Linking,
  author = {Savary, Onaïa and Ardilouze, Constantin and Cattiaux, Julien},
  title = {Linking European droughts to year-round weather regimes},
  journal = {Weather and Climate Dynamics},
  year = {2026},
  doi = {10.5194/wcd-7-223-2026},
  url = {https://doi.org/10.5194/wcd-7-223-2026}
}

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