To understand the violence of this event, we must understand the meteorological context that prevailed at that time. The episode of bad weather is first caused by upwellings of mild and unstable air coming from the Mediterranean, and it is accentuated by the presence of two ex-hurricanes, Leslie over Spain and Michael over Catalonia.
These unstable rises, blocked in their progress by an anticyclone which resists from Tunisia to the Alps, are accompanied by heavy stormy rains which then concentrate on the plains of Aude and the Cévennes giving exceptional accumulations of rain in a short time .
Remarkable accumulations in 8 hours
© The Weather Channel
On average, 130 mm falls in the center of Aude (a third of the department) but in places the accumulations are much higher.
In Trèbes, near Carcassonne, we recorded 296 mm in the space of 8 hours, including 185 mm in just 4 hours and 55 mm in one hour. In the Pyrénées-Orientales, average accumulations reach 70mm and approach 150mm on the edge of Aude. We note 190 mm in Lasbastide (81) and almost 150 mm on the Hérault reliefs. In the Cévennes, the rains continue into the night. The total reaches the impressive height of 301 mm in Castanet-le-Haut.
Flash floods and flooding
© The Weather Channel
These very intense precipitation then lead to a very brutal reaction of the watercourses. The level of the Aude at Trèbes increases from 50 cm to more than 7 meters in the space of 6 hours. This flash flood is also a 100-year flood, since such a height of water has not occurred since 1891.
© The Weather Channel
Usual episodes around the Mediterranean
The Mediterranean climate is made up of contrasts, with alternating long periods of drought and intense rainy episodes which often return at the same time of year: in autumn. This recurring phenomenon is called “Mediterranean monsoon” by geographers, even if the term “monsoon” at first glance evokes the climate of India. And yet, other climates have similarities, such as the southern United States, and to a lesser extent the Mediterranean. It is in this context that the south-east of France often faces devastating floods at this time of year.
© The Weather Channel
