Heavy precipitation and strong winds in storm Darragh locally strengthened by human-driven climate change

Contact Authors

• Tommaso Alberti, INGV, Italy  📨tommaso.alberti@ingv.it  🗣️Italian, English

• Mireia Ginesta, Oxford University, UK 📨mireia.ginesta@smithschool.ox.ac.uk 🗣️Spanish, English

• Flavio Pons, IPSL, France  📨flavio.pons@lsce.ipsl.fr  🗣️Italian, English, French

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

Citation

• Alberti, T., Ginesta, M., Pons, F. M. E., & Faranda, D. (2024). Heavy precipitation and strong winds in storm Darragh locally strengthened by human-driven climate change. ClimaMeter, Institut Pierre Simon Laplace, CNRS. https://doi.org/10.5281/zenodo.14341702

Press Summary  (First published 2024/11/19)

• Storms similar to Darragh are up to 2 hP deeper, up to 4km/h  (5%) windier over the Atlantic coasts of Ireland and France, and  up to 5mm/day ( up to 10%) wetter  in the present than they would have been in the past

• Storm Darragh was driven by very exceptional meteorological conditions.

• We ascribe the strengthened winds and heavier precipitation of Storm Darragh to human-driven climate change.

Starting from December 6, 2024, our analyses integrate ERA5 data, providing coverage from 1950 with a latency of approximately 5 days and GFS forecasts, for the most recent days where ERA5 data is not yet available.

Event Description

On December 5, 2024, a depression approaching Ireland and the UK was named Darragh by the MetOffice, becoming the fourth named storm of the 2024-2025 season. Between December 6 and 7, Darragh intensified and rapidly crossed Ireland and the United Kingdom as a very strong Atlantic storm, bringing heavy rainfall and hurricane-force winds, exceeding 160 kilometers per hour. The storm caused widespread power outages, leaving nearly 400,000 homes and businesses in Ireland without electricity (The Times). In the UK, two fatalities were reported due to falling trees, and approximately 130,000 households experienced power cuts (CNews). Transportation networks faced significant disruptions, with numerous flight cancellations, train service suspensions, and road closures due to debris and flooding (The Sun). The Met Office issued rare red weather warnings, indicating a high potential for structural damage and danger to life (BBC).  

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 up to 4 °C over continental Europe, particularly over 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 40 mm/day) over Ireland, UK, and North Sea. Windspeed data shows large areas of Europe and Atlantic affected by winds between 40 km/h and 60 km/h.

Climate and Data Background for the Analysis

The IPCC AR6 WG1 report states that climate change affects storminess in Europe, with negative repercussions that are exacerbated by rising sea levels and heavy precipitation. Extreme precipitation and pluvial flooding are projected to increase at global warming levels exceeding 1.5°C in all regions except the Mediterranean (high confidence). In a warmer climate, individual midlatitude storms are expected to produce more precipitation. However, due to the unequal warming between ocean and land, alteration in atmospheric circulation patterns may result in diminished continental near-surface relative humidity and localised decreases in precipitation. Changes in wind speed remain less certain. Studies, such as Ginesta et al. (2024), found 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 Darragh, we have low confidence in the robustness of our approach given the available climate data, as the event is very exceptional 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)  [-10°W 10°W 45°N 60°N]. Surface pressure changes indicate that storms resembling Darragh exhibit pressure anomalies up to 2 hPa deeper over Northern Ireland and Scotland in the present than in the past. Temperature changes do not show significant variations with respect to the past. Precipitation changes indicate wetter conditions (+5 mm/day) over Northern Ireland and Scotland, as well as over Southern France, while drier conditions (-5 mm/day) are observed over Norway. Windspeed changes suggest that these storms are now up to 4 km/h windier over North-Western France and Western Ireland. From the analysis in the urban areas we found that Inverness (Scotland), Glasgow (Scotland), and Brest (France) are getting wetter in the present than in the past during storms similar to Darragh, with Dublin and Bristol also experiencing windier conditions. We also note that Similar Past Events display similar seasonal distribution between past and present periods.

Finally, we find that sources of natural climate variability may have not influenced the event. This suggests that the changes we see in the event compared to the past are mainly due to human driven climate change.

Conclusion

Based on the above, we conclude that windstorms similar to Storm Darragh are more intense with up to 2 hP deeper, up to 4 km/h  (5%) windier over the Atlantic coasts of Ireland and France, and  up to 5mm/day ( up to 10%) wetter  in the present than they would have been in the past. We interpret Storm Darragh as an event driven by very exceptional meteorological conditions whose characteristics can be ascribed to human driven climate change.