A recent study has analysed for the first time the occurrence of derechos in France, particularly during the ‘hot season’ from May to September. Between 2000 and 2022, 38 events of this type were recorded, with an average frequency of 1.7 events per year, i.e. almost 5 events every 3 years.
Severe thunderstorms are less studied in Europe than in the United States. However, a recent event has highlighted the very real threat that they represent for Europeans too. During the night of 17 to 18 August 2022, a line of thundery squalls formed near the Balearic Islands, moving rapidly north-eastwards and affecting Corsica, Italy, Slovenia, Austria and then the Czech Republic in just 12 hours. Wind gusts of up to 225 km/h in Corsica killed 12 people and injured 106 others, as well as causing extensive material damage. This event falls into the “derecho” category: a complex of thunderstorms extending over more than 100 km and characterised by the production of violent wind gusts in excess of 90 km/h over a wide area.
A recent study has analysed for the first time the occurrence of derechos in France, particularly during the ‘hot season’ from May to September. Between 2000 and 2022, 38 events of this type were recorded, with an average frequency of 1.7 events per year, i.e. almost 5 events every 3 years. These storms, often associated with a south-westerly flow, affect almost the whole of France, but their frequency is higher in the north-east and east of the country, with events also often affecting Switzerland, the Benelux countries and Germany. This study thus contributes to a better characterisation of the risk associated with these extreme weather events in France and Europe.
In addition, the study examines the atmospheric conditions of instability and vertical wind shear that characterise the potential of a meteorological situation to produce a severe thunderstorm event. The authors find an increase in instability coinciding with higher surface temperatures in the recent period, for situations similar to those associated with the thunderstorm events identified. These results corroborate previous studies that have made a similar observation in Europe. This increase in instability, which reflects the potential for more intense storms, is an expected effect of man-made global warming. However, in the context of this study, the influence of natural climate variability cannot be ruled out.
Reference
Fery, L. and Faranda, D.: Analysing 23 years of warm-season derechos in France: a climatology and investigation of synoptic and environmental changes, Weather Clim. Dynam., 5, 439–461, https://doi.org/10.5194/wcd-5-439-2024, 2024.
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