Downpours. Hérault and Gard were placed by Météo-France on red “rain-flood” alert on Wednesday September 30, due to an “exceptional Mediterranean episode”. In Saint-Hippolyte-du-Fort (Gard), 337.6 mm of rain fell between Tuesday evening and Wednesday evening, the equivalent of 61 days of rain in one day, according to Météo-France records. In Colognac, in the same department, 299 mm of water fell over the same period, or 54 days of rain. In Prades-le-Lez (Hérault), the equivalent of 71 days of rain fell in 24 hours (264.9 mm).
Mediterranean episodes (previously called "Cévennes") are characterized by large quantities of water dumped in a short time over a restricted area. These significant, very localized accumulations of rain are caused by the stagnation of storm systems, blocked by the relief. The consequences depend largely on the topography and can vary significantly depending on the areas and slopes.
Conditions met from September to December
Mediterranean episodes are subject to numerous constraints: they do not appear just anywhere, and they do not appear at any time of the year. They occur “most often in autumn, from September to December”, researcher Cécile Caillaud, from the National Meteorological Research Center, explains to franceinfo. The most significant disasters all occurred during this season: the deadly floods of the Roya valley (Alpes-Maritimes), in 2020, took place in October, like those of Nîmes (Gard), in 1988. Those of Vaison-la-Romaine (Vaucluse), in 1992, took place in September.
It is at this time of year that the conditions make their appearance possible: “Cold air at altitude and rises of warm, humid air at low level with a Mediterranean Sea that is still warm after summer,” explains this specialist in Mediterranean episodes. “This cold air comes from the polar or northern regions and it follows the meanders of the jet stream, this high-altitude air current which separates the polar air masses and the mild air masses,” explains Météo-France in a video published on September 29. “Sometimes it dips south and it takes cold air with it.”
It is for this reason that the authorities are launching their prevention campaign on Mediterranean episodes at the end of summer. In 2026, it began on September 11. In 2025, the Ministry of the Interior launched the tenth of its kind on September 19. These campaigns are aimed at residents of the fifteen departments around the Mediterranean "most exposed to these episodes": Alpes-de-Haute-Provence, Alpes-Maritimes, Ardèche, Aveyron, Aude, Bouches-du-Rhône, Corse-du-Sud, Haute-Corse, Drôme, Gard, Hérault, Lozère, Pyrénées-Orientales, Var and Vaucluse, lists the government.
If Mediterranean episodes occur mainly in autumn, is it possible to establish a parallel between their season and that of cyclones, which extends "every year, from June to November", as reported by the prefecture of Guadeloupe? “I don’t think we can compare them directly,” climatologist Davide Faranda, a specialist in extreme phenomena, responds to franceinfo. 'Hurricanes constitute a well-defined family of phenomena, while Mediterranean episodes correspond to different meteorological configurations,' he explains.
A still unclear development
Already becoming more intense under the influence of global warming linked to human activities, will the Mediterranean episodes also shift in time? Will climate change, which tends to modify the cycle of the seasons with longer summers and shorter winters, also affect the calendar of these phenomena? “A warmer Mediterranean Sea can increase the intensity of precipitation when the atmospheric conditions are right, but this does not mean that the episodes will gradually shift towards January or February,” says Davide Faranda.
“We are starting to have the tools to study the change in seasonality. Some initial studies have been carried out, but not with large ensembles,” explains Cécile Caillaud.
“The first results show that the main season of Mediterranean episodes will remain in autumn. It is this season which remains the moment which is most favorable to them."
Cécile Caillaud, climatology researcher
at franceinfo
In fact, certain Mediterranean episodes are already possible in winter, as the one in January 2026 showed. “But they are generally more frequent and more intense in autumn, when the Mediterranean is still very warm after summer,” notes Davide Faranda. They also already happened earlier in the year. In 2010, in Draguignan, in the Var, 25 people were killed during terrible floods with some 460 mm of precipitation in one day. “It was in June,” points out Cécile Caillaud. The fact remains that now, as in the near future, the vast majority of these events will continue in autumn, insists the scientist, who already knows that the question of seasonality will occupy her in the coming years.
