Wildfires in southwestern France generate pyrocumulonimbus clouds, firefighters face unpredictable firestorms

In Gironde, emergency crews are continuously battling massive forest fires. They face a dangerous and still unknown adversary.

Published: July 29, 2026, 7:51 PM

Can sometimes create their own weather: huge smoke clouds during forest fires in France. Photo: Emma Da Silva / AP

From Paris Rudolf Balmer

In southwestern France, emergency crews continued the fight against the massive forest fire near Bordeaux – but the weather is causing additional difficulties. Temperatures of up to 42 degrees Celsius were expected in the Gironde department on Wednesday, which could worsen the drought in the region and pave the way for new flames. Forecast winds threaten to undo the progress of firefighting forces. And recently, the fire itself created destructive weather with so-called firestorms.

In California and Australia, the meteorological phenomenon Pyrocumulonimbus has been observed in recent years during mega forest fires. In Gironde, however, the kilometer-high fire clouds that form during wildfires and then cause their rapid and unpredictable spread are completely new.

Challenges Posed by Firestorms

Firestorms pose enormous problems for firefighters constantly battling the blazes. They are cited as the reason why, after about 10 days, the fire sources west of Bordeaux are still not under control. Sporadically, sometimes violently, fires break out again and again.

Researcher Jean-Baptiste Filippi, head of the Fire Caster study program, explained the phenomenon in the French newspaper Le Monde:

"The fire creates its own wind, with quadruple the force and speed."

"Blowing on the Embers with Force"

Wind columns form that suck burning branches upward and even uproot trees. "They then drop these wind columns 100 or 200 meters away, where they ignite new fires." Vortices also form, having an effect comparable to that of an open fireplace: "It's like blowing on the embers with insane force."

"The fire creates its own favorable weather conditions." — Christophe Chantepy, National Forestry Office (ONF)

Some of the fire clouds can even trigger their own lightning: Due to the heat of the fire, smoke columns spiral so high that ice forms at altitude. High electrical voltage discharges, similar to a normal thunderstorm, as lightning – which can in turn ignite new fires.

Climate Crisis and Fire Risk

Globally, the climate crisis is increasing the risk of forest fires. With more severe forest fires, firestorms can also occur more frequently. Relatively humid winters allow a lot of growth. This dries out during increasingly longer dry periods in summer, followed by extreme heat. The result: a lot of easily flammable material.

Additionally, firestorm clouds can themselves further fuel the climate crisis. Soot particles are hurled into the upper layers of the atmosphere, where they then contribute to the warming of the air layers.

Firestorms Are Unpredictable

In the fight against the inferno near Bordeaux, firestorms are an unpredictable adversary. "This is dangerous because the fire creates its own favorable weather conditions," said Christophe Chantepy from the National Forestry Office (ONF). Specifically, this meant that emergency crews had practically controlled the fire on one front. But then new fires suddenly broke out in unexpected places, or fires rekindled due to embers still smoldering in the ground.

This "incredible, unexpected, and previously unknown phenomenon" of Pyrocumulonimbus occurred multiple times in Gironde, emphasized Prefect Sophie Brocas, as a representative of the central government, before journalists.

Since authorities in this region had to evacuate more than 200,000 people.