Brennan et al. (2025) Insights from hailstorm track analysis in European climate change simulations

Identification

• Journal: Natural hazards and earth system sciences
• Year: 2025
• Date: 2025-10-01
• Authors: Killian P. Brennan, Iris Thurnherr, Michael Sprenger, Heini Wernli
• DOI: 10.5194/nhess-25-3693-2025

Research Groups

• Institute for Atmospheric and Climate Science, ETH Zürich, Zurich, Switzerland
• Institute of Geography – Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Short Summary

This study investigates the impact of a 3 K global warming scenario on European hailstorms using kilometer-scale climate simulations and an object-based tracking algorithm. It reveals significant shifts towards more intense hailstorms with larger hail diameters, expanded swath areas, and increased associated hazards (precipitation, wind), driven by enhanced convective available potential energy and specific humidity.

Objective

• To assess the impact of 3 K global warming on hailstorm dynamics and environmental conditions across Europe using advanced numerical climate modeling and object-based analysis.
• To quantify changes in hailstorm lifetime, area, and propagation speed.
• To determine how hail swath area changes with global warming, particularly concerning different hail sizes.
• To analyze changes in the magnitude and structure of convective available potential energy (CAPE), convective inhibition (CIN), vertical wind shear, specific humidity, and potential temperature in the hailstorm environment.
• To investigate the geographical variability of climate change effects on hailstorm characteristics and environments across Europe.
• To evaluate changes in storm-associated hazards, such as precipitation and wind, along hailstorm tracks.

Study Configuration

• Spatial Scale: Europe, with a horizontal grid spacing of 2.2 km, enabling convection-permitting resolution.
• Temporal Scale: Two 11-year periods (2011–2021) for current and future climate scenarios, with high-frequency hail output at 5 minute intervals. The future climate scenario corresponds to a +3 K global temperature increase via a pseudo-global warming approach.

Methodology and Data

• Models used: COSMO v6 (non-hydrostatic, limited-area numerical weather prediction model) and HAILCAST (online diagnostic hail growth parameterization).
• Data sources: ERA5 reanalysis data (for driving COSMO at lateral boundaries). High-frequency (5 minute) hail diameter output from COSMO simulations. Object-based hailstorm tracking algorithm (Brennan et al., 2025a) applied to identify and track hailstorms. Storm-centered composites were constructed from atmospheric fields within a 60 km radius of storm centers.

Main Results

• Hailstorm Frequency and Distribution: Hail frequency trends vary regionally across Europe; increases are projected for northeastern Italy, southern Austria, and Slovenia, while decreases are seen from the Iberian Peninsula through France, northwestern Italy, northern Germany, and northern Poland.
• Hail Size and Swath Area: A 2-fold increased frequency of storms producing hail diameters of approximately 50 mm and larger is projected. Per-storm hail swath areas generally expand by 15 %–30 %, with increases being more significant for smaller hail (e.g., +38 % for 15 mm hail), while frequency changes dominate for larger hail (above 40 mm). Mean storm maximum hail diameters are projected to increase by +1 to +4 mm across most of Europe (+3.6 % domain-wide).
• Storm Characteristics: Mean instantaneous storm areas increase by +10.3 % domain-wide (up to +40 km²). Mean storm propagation velocity increases by +7.3 % domain-wide (up to +1 to +3 m/s). Mean storm lifetime shows a weak increase of +1.7 % domain-wide, with high spatial variability.
• Environmental Changes: The inflow environment of hailstorms shows increased mean CAPE (+5.5 %), CIN (+15.7 %), vertical wind shear (+6.0 %), and total column water vapor (+14.5 %). Inflow areas are projected to be 1.83 K warmer at 850 hPa.
• Melting Effects: The effect of increased hail melting due to a higher 0 °C level is found to be minor for storm maximum hail diameters greater than 15 mm, primarily affecting only the smallest hail diameters (≤11 mm).
• Associated Hazards: Precipitation and wind hazards accompanying hailstorms are expected to increase on average by 20 % and 5 %, respectively. Extreme hail–precipitation compound events (hail with a diameter of at least 30 mm followed by 50 mm/h of rainfall) are projected to be twice as frequent in the future.

Contributions

• First study to apply an object-based hailstorm-tracking algorithm to kilometer-scale climate simulations to analyze the impact of climate change on hailstorms in Europe.
• Provides a comprehensive, nuanced understanding of hailstorm evolution and variability under future climatic conditions, going beyond traditional Eulerian analysis by quantifying changes in individual storm characteristics (e.g., lifetime, area, propagation speed, hail swath area).
• Reveals that while hailstorm frequency trends vary regionally, changes in hailstorm properties (e.g., size, area, propagation velocity) and environmental conditions (e.g., CAPE, specific humidity) are surprisingly consistent across regions.
• Quantifies the projected increase in compound hazards, specifically intense rainfall immediately following hail, which is critical for damage assessment.
• Generates and makes available an extensive dataset of approximately 40,000 hail swaths for both current and future climates, suitable for stochastic resampling and application in hail damage models.

Funding

• Swiss National Science Foundation (SNSF) Sinergia grant CRSII5_201792

Citation

@article{Brennan2025Insights,
  author = {Brennan, Killian P. and Thurnherr, Iris and Sprenger, Michael and Wernli, Heini},
  title = {Insights from hailstorm track analysis in European climate change simulations},
  journal = {Natural hazards and earth system sciences},
  year = {2025},
  doi = {10.5194/nhess-25-3693-2025},
  url = {https://doi.org/10.5194/nhess-25-3693-2025}
}