Häberli et al. (2026) Unprecedented extreme meteorological droughts simulated in Fenno-Scandinavia with high-resolution climate models

Identification

• Journal: Climate Dynamics
• Year: 2026
• Date: 2026-03-01
• Authors: Ruben Häberli, OB Christensen, Peter Thejll, Eigil Kaas
• DOI: 10.1007/s00382-026-08060-z

Research Groups

• Physics of Ice, Climate and Earth, Niels Bohr Institute, University of Copenhagen, Denmark
• National Centre for Climate Research, Danish Meteorological Institute, Denmark

Short Summary

This study assesses future meteorological drought probabilities in Fenno-Scandinavia using high-resolution convection-permitting regional climate models (CPRCMs) and a novel multi-threshold Standardized Precipitation Index (SPI) method. It projects a decrease in moderate droughts but a significant increase in unprecedented extreme droughts, particularly during the critical growing season, highlighting the added value of CPRCMs.

Objective

• To improve understanding of changes in drought frequency for different intensities in Fenno-Scandinavia, especially during the growing season (May-July).
• To investigate the differences between a Convection-Permitting Regional Climate Model (CPRCM) and a Regional Climate Model (RCM) to assess the added value for drought projections.

Study Configuration

• Spatial Scale: Fenno-Scandinavia (Norway, Sweden, Finland, Denmark), divided into nine sub-regions. Model resolutions of approximately 3 kilometers (CPRCM) and 12 kilometers (RCM).
• Temporal Scale: Historical (calibration) and future scenarios, each spanning 20-year periods: historical (CTRL), mid-century (MC: 2041-2060), and late-century (LC: 2081-2100).

Methodology and Data

• Models used:
  • HARMONIE-Climate regional climate model cycle 38 (HCLIM-38) at 3 kilometers (CPRCM, HCLIM3) and 12 kilometers (RCM, HCLIM12) grid spacing.
  • Global Climate Models (GCMs) for dynamic downscaling: EC-Earth (ECE) and GFDL-CM3 (GFDL).
• Data sources:
  • Precipitation data from the NorCP project's HCLIM simulations.
  • Standardized Precipitation Index (SPI) with 1-month (SPI-1) and 3-month (SPI-3) accumulation periods.
  • A novel multi-threshold method developed for analyzing standardized drought indices.
  • Representative Concentration Pathways (RCP) scenarios: RCP4.5 and RCP8.5.

Main Results

• Moderate drought frequency (SPI < -1) is projected to decrease across Fenno-Scandinavia in future scenarios.
• The frequency of exceptional (SPI < -3) and unprecedented (SPI < -4) droughts is projected to increase significantly, with unprecedented droughts appearing in almost all future scenarios and regions, even though they did not occur in the historical period.
• During the growing season (May-July), the decrease in moderate drought frequency disappears, and a much larger increase in exceptional and unprecedented drought frequencies is observed compared to annual averages.
• Both the CPRCM (3 km resolution) and RCM (12 km resolution) show a similar overall signal of fewer moderate but more intense droughts.
• The CPRCM projects a higher frequency of droughts, particularly for the most intense short-term meteorological droughts (SPI-1), compared to the RCM.
• Spatially, Southern Finland, Denmark, and Southern Sweden are projected to experience the largest increases in the most intense droughts.

Contributions

• First study to analyze drought conditions and the benefits of using a convection-permitting regional climate model (CPRCM) for drought analysis in Fenno-Scandinavia using the NorCP project data.
• Introduction of a novel drought multi-threshold method for standardized drought indices, enabling a more comprehensive analysis of drought frequency across multiple intensity levels (moderate, extreme, exceptional, unprecedented).
• Provides new insights into future drought dynamics in Fenno-Scandinavia, challenging existing projections by revealing an increase in extreme droughts despite an overall increase in precipitation, especially during the critical growing season.
• Demonstrates the added value of CPRCMs in projecting more intense short-term meteorological droughts compared to RCMs, emphasizing the importance of higher-resolution models for accurate drought analysis.

Funding

• Danish government through the National Centre for Climate Research (NCKF)
• Nordic modelling collaboration (NorCP)
• Open access funding provided by Copenhagen University

Citation

@article{Häberli2026Unprecedented,
  author = {Häberli, Ruben and Christensen, OB and Thejll, Peter and Kaas, Eigil},
  title = {Unprecedented extreme meteorological droughts simulated in Fenno-Scandinavia with high-resolution climate models},
  journal = {Climate Dynamics},
  year = {2026},
  doi = {10.1007/s00382-026-08060-z},
  url = {https://doi.org/10.1007/s00382-026-08060-z}
}