Heavy precipitation and strong winds in storm Éowyn mostly strengthened by human-driven climate change

Contact Authors

• Davide Faranda, IPSL-CNRS, France  📨davide.faranda@lsce.ipsl.fr  🗣️French, Italian, English

• Flavio Pons, IPSL, France  📨flavio.pons@science-partners.com 🗣️Italian, English, French

• Marco Reale, National Institute of Oceanography and Applied Geophysics-OGS,Italy, 📨mreale@ogs.it, 🗣️Italian, English

• Mireia Ginesta, Oxford Sustainable Law Programme, University of Oxford mireia.ginesta@smithschool.ox.ac.uk, Catalan, Spanish, English

• Greta Cazzaniga, IPSL-CNRS, France 📨 greta.cazzaniga@lsce.ipsl.fr 🗣️Italian, English, French

• Erika Coppola, ICTP, Italy 📨 coppolae@ictp.it 🗣️Italian, English

Citation

• Faranda, D., Pons, F. M. E., Reale, Marco, Ginesta, M., Cazzaniga, G., & Coppola, E. (2025). Heavy precipitation and strong winds in storm Éowyn mostly strengthened by human-driven climate change. ClimaMeter, Institut Pierre Simon Laplace, CNRS. https://doi.org/10.5281/zenodo.14755395

Press Summary (First published 2025/01/28)

• Storms similar to Éowyn are up to 4 hP deeper, up to 8 km/h  (10%) windier over the Atlantic coasts of Ireland and France, and up to 6 mm/day (up to 15%) wetter in the present than they would have been in the past.

• Storm Éowyn was driven by very rare meteorological conditions.

• We mostly ascribe the strengthened wind and higher precipitation of Storm Éowyn to human-driven climate change and natural climate variability likely played a modest role.

Event Description

Storm Éowyn, an exceptionally powerful extratropical cyclone, struck Ireland, the Isle of Man, and the United Kingdom on January 24, 2025. Named by the UK Met Office on January 21, 2025, it was the fifth storm of the 2024–25 European windstorm season. While approaching Ireland and the UK, Éowyn underwent a phase of explosive intensification, with an exceptional pressure drop of 50 hPa in 24 hours, leading to a minimum observed value of 939 hPa.  Éowyn displayed unprecedented wind speeds, with sustained wind above 80 mph (135 km/h) and gusts reaching up to 135 mph (217 km/h) in Cairnwell, Scotland, making it comparable to a category 1 hurricane, leading to widespread red weather warnings across the affected regions (Wikipedia). The impact of Storm Éowyn was devastating. Over 1 million people in Ireland, Northern Ireland, and Scotland were left without electricity and sustained significant property damage, including the collapse of a 100-year-old building in Hale, Manchester, and the fall of a 166-year-old Himalayan cedar at the Royal Botanic Garden Edinburgh. Tragically, the storm claimed two lives, both due to falling trees. In response to the widespread damage, international support crews from Finland, Austria, and France were flown in to expedite recovery efforts (see APNews,The Irish Sun, The Times & The Sunday Time,The Sun).

The Surface Pressure Anomalies reveal a large negative (cyclonic) anomaly over the UK and Central Europe. In the context of Atlantic extratropical storms, this setup can be associated with extensive precipitation and intense wind due to the deepening pressure gradient. Temperature Anomalies show temperatures up to 4 °C warmer than average over continental Europe, particularly in Northern France, Belgium, The Netherlands, and Northern Germany, extending up to Denmark and the UK (2 °C), affected by the warm sector of the cyclone. Precipitation Data show intense daily precipitation (up to 50 mm/day) over Ireland, UK, France and North Sea. Windspeed data show large areas of Europe and Atlantic affected by sustained winds between 40 km/h and 60 km/h, and higher than 60 km/h over the sea and the coasts of Ireland and Scotland.

Climate and Data Background for the Analysis

The IPCC AR6 Chapter 11 states that climate change affects storminess in Europe, with negative repercussions that are exacerbated by rising sea levels and heavy precipitation. From a global warming level of 2 °C or higher a slightly increased frequency and amplitude of extratropical cyclones, strong winds and extratropical storms is projected for northern Europe with medium confidence (IPCC AR6 WGI Chapter 12). The extreme precipitation and pluvial flooding have shown a strong trend in Northern Europe in the past and there is a strong consensus among models from global to kilometer scale convection permitting models that are going to increase from 2 °C or higher  (IPCC AR6 WGI Chapter 12). Studies, such as Ginesta et al. (2024), confirm that the intensity of recent storms, including both wind speed and precipitation, is likely to increase in the most impacted regions of Europe.

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For storm Éowyn, we have medium-high confidence in the robustness of our approach given the available climate data, as the event is similar to other past events in the data record.

ClimaMeter Analysis

We analyze here (see Methodology for more details) how events similar meteorological conditions have changed in the present (1987–2023) compared to what they would have looked like if they had occurred in the past (1950–1986) in the region [20°W 10°E 45°N 65°N]. Surface pressure changes indicate that storms resembling Éowyn exhibit pressure anomalies up to 4 hPa deeper over Northern Ireland in the present than in the past. Temperature changes show up to 5°C warmer anomalies with respect to the past, especially over Scandinavia. Precipitation changes indicate wetter conditions (+6 mm/day) over Northern Ireland and Scotland, as well as over Northern France, and Norway. Windspeed changes suggest that these storms are now up to 8 km/h windier over Scotland, Ireland and the English Channel. From the analysis of urban areas, we found that Dublin, Galway, and Cork all experience up to 4k m/h windier conditions. We also note that Similar Past Events display comparable seasonal distribution between past and present periods.

Finally, we find that sources of natural climate variability, notably the Atlantic Multidecadal Oscillation, may have only partly influenced the event. This means that the changes we see in the event compared to the past may be mostly due to human-driven climate change.

Conclusion

Based on the above, we conclude that windstorms similar to Storm Éowyn are more intense with up to 4 hP deeper, up to 8 km/h  (10%) windier over the Atlantic coasts of Ireland and France, and up to 6 mm/day ( up to 15%) wetter in the present than they would have been in the past. We interpret Storm Éowyn as an event driven by rare meteorological conditions whose characteristics can be mostly ascribed to human-driven climate change.