Mishra et al. (2025) Long-lasting intense cut-off lows to become more frequent in the Northern Hemisphere

Identification

• Journal: Communications Earth & Environment
• Year: 2025
• Date: 2025-02-15
• Authors: Aditya N. Mishra, Douglas Maraun, R. Schiemann, Kevin I. Hodges, Giuseppe Zappa, Albert Ossó
• DOI: 10.1038/s43247-025-02078-7

Research Groups

• Wegener Center for Climate and Global Research, University of Graz, Graz, Austria
• National Centre for Atmospheric Science, Department of Meteorology, University of Reading, Reading, UK
• Institute of Atmospheric Sciences and Climate, Italian National Research Council, Bologna, Italy

Short Summary

This study projects future changes in Northern Hemisphere Cut-off Lows (COLs) using CMIP6 models under the SSP5-8.5 scenario, finding that long-lasting, intense COLs will become more frequent over land in spring, potentially increasing related hazards. An increase in COL propagation velocity, however, may partly offset this increase in hazard.

Objective

• To assess how climate change will impact the frequency of Cut-off Lows (COLs) in the Northern Hemisphere.
• To determine how the most intense and long-lasting COLs are affected by climate change.
• To analyze how the propagation velocity of COLs will change with climate change.

Study Configuration

• Spatial Scale: Northern Hemisphere, focusing on land regions (Europe, North America, Asia-N. Pacific) and major oceanic regions (Mediterranean Sea, Western Atlantic, East Pacific).
• Temporal Scale:
  • Historical period: 1950–2014 (CMIP6 models), 1979–2014 (ERA5 reanalysis).
  • Future period: 2071–2100 (CMIP6 models under SSP5-8.5 emission scenario).
  • Seasonal analysis: Winter, Spring, Summer, Autumn.
  • COL duration classes: 1–3 days (short-lasting) and >3 days (long-lasting).

Methodology and Data

• Models used: 18 Coupled Model Intercomparison Project Phase 6 (CMIP6) models, including standard and HighResMIP models.
• Data sources:
  • ERA5 reanalysis (European Centre for Medium-Range Weather Forecasts): Relative vorticity at 250 hPa, 6-hour timesteps, spatial resolution of approximately 31 km (TL639).
  • CMIP6 models: Zonal (ua) and meridional (va) wind data at 250 hPa, 6-hour timesteps.
• Algorithms/Methods:
  • TRACK algorithm: A feature-tracking algorithm used to detect and track COLs.
  • COL detection criteria: Relative maxima of 250 hPa relative vorticity greater than 1.0 × 10⁻⁵ s⁻¹.
  • Preprocessing: Spectral filtering (T42 truncation) and removal of large-scale background.
  • Filtering: Four-point wind filtering to identify cyclonic circulation and exclude open troughs.
  • Duration: Only systems lasting at least 24 hours (four consecutive 6-hour frames) are considered.
  • Intensity classification: Low intensity (maximum intensity ≤ 10 × 10⁻⁵ s⁻¹) and high intensity (maximum intensity > 10 × 10⁻⁵ s⁻¹).

Main Results

• Overall COL Frequency: A small median increase of 5% in COL frequency is projected over Europe in winter, transitioning to a more substantial median increase of 20% in spring (with statistically significant increases up to 50% in some central and northern European areas). North America shows a 15% median increase in spring. Asia-N. Pacific projects a 20% median increase in winter, with surges also in spring and autumn. Conversely, a decline in COL frequency is projected for summer over North America and Asia-N. Pacific.
• Long-lasting COLs (>3 days): These are projected to become more frequent over Europe in spring and summer (15/18 and 16/18 models show an increase, respectively, with a mean rise of up to 70% in certain central and northern European areas). Increases are also projected for spring over North America and Asia-N. Pacific.
• High-intensity COLs (>10 × 10⁻⁵ s⁻¹): While projected to decrease over oceans in summer, a significant surge is projected over land regions in winter, spring, and autumn. Specifically, Europe and Asia-N. Pacific show a 20% median increase in spring (17/18 models), and North America projects a 10% median increase in spring (15/18 models).
• Propagation Velocity: COL propagation velocity is projected to increase in winter and spring over Europe and North America, potentially leading to faster-moving COLs. However, in summer, a considerable decrease in COL propagation velocity is projected over North America and Asia-N. Pacific (18/18 models project a decrease over North America).
• Jet Stream Linkages: Projected changes in the jet stream, including a poleward shift and regional weakening/strengthening of zonal flow, are dynamically linked to and corroborate the projected changes in COL frequency.

Contributions

• First comprehensive multi-model assessment of future changes in Cut-off Lows (COLs) characteristics (frequency, duration, intensity, propagation velocity) using CMIP6 models under a high-emission scenario (SSP5-8.5).
• Identifies a critical projected increase in the frequency of long-lasting and intense COLs over populated land regions of the Northern Hemisphere, particularly in spring, suggesting an extension of the COL season in Europe.
• Highlights the potential for increased heavy rainfall-related hazards due to more frequent intense COLs, while also noting the possible partial offset from increased COL propagation velocity in some seasons.
• Provides insights into the dynamical linkages between projected COL changes and shifts in the jet stream, Rossby wave breaking, and atmospheric blocking.

Funding

• Austrian Climate Research Program (Project CHIANTI, KR19AC0K1 7553)
• Austrian Science Fund (FWF; Research Grant W1256, Doctoral Program Climate Change: Uncertainties, Thresholds and Coping Strategies)
• UK National Centre for Atmospheric Science (NCAS)
• NERC CANARI project (NE/W004984/1)

Citation

@article{Mishra2025Longlasting,
  author = {Mishra, Aditya N. and Maraun, Douglas and Schiemann, R. and Hodges, Kevin I. and Zappa, Giuseppe and Ossó, Albert},
  title = {Long-lasting intense cut-off lows to become more frequent in the Northern Hemisphere},
  journal = {Communications Earth & Environment},
  year = {2025},
  doi = {10.1038/s43247-025-02078-7},
  url = {https://doi.org/10.1038/s43247-025-02078-7}
}