Changes in synoptic circulations associated with documented derechos over France in the past 70 years

Abstract. Derechos are a type of severe windstorm characterized by a swath of wind damage several hundred kilometers long. They are known to cause widespread damage and can have a significant impact on human safety and infrastructure. A recent example is the European derecho of 18 August 2022 that produced damaging surface wind gusts (>200 km/h) and affected Corsica, Italy and Austria within 12 hours. The goal of this paper is to analyse recent derechos in France in the satellite era and assess the role of climate change in modifying their characteristics. We identify eleven (11) events in the past and provide their tracks retrieved using the ERA5 reanalysis dataset. To detect climate change signal, we compare cyclonic atmospheric circulations (low pressure systems) that can lead to derechos in the distant past (1950–1979), when warming was just beginning, and in the recent past (1993–2022). Two of the events are found to be unprecedented, that is no good analogues can be found in at least one period and attribution statements cannot be made on the basis of the present analysis. For most of the other events, instead, we find a significant signal of increased precipitation in the recent period which, without change in circulation, is explained by higher temperatures. For these events there is also not a clear change in depth of the low pressure system trigger. Finally, we can exclude the role of climate variability of El Nino (ENSO) in most of the events, while we cannot rule out the influence of the Atlantic Multidecadal Oscillation (AMO) in favoring low pressure systems possibly leading to derechos.