France wildfire fight faces fire clouds with 150 km/h updrafts and lightning risk

Firefighters battling severe wildfires in France are facing pyrocumulonimbus clouds, fire-driven storms that can generate powerful winds and lightning and make blazes harder to control.

French wildfire researcher Jean-Baptiste Filippi told AFP that the clouds, also known as fire clouds, remain relatively new in France and are another consequence of human-caused climate change.

A fire cloud forms when a column of heated air rises above a blaze. A small cumulus cloud can develop into a much larger cumulonimbus cloud as hot air and water vapour feed the storm.

Filippi said the system can produce updrafts of more than 150 kilometres an hour.

Rain may evaporate before reaching the ground, while cooling air can create strong downdrafts. Lightning generated by the storm can also ignite new fires.

The phenomenon is common in Portugal, California and Australia, where firefighters have more experience dealing with it.

Filippi said pyrocumulonimbus clouds were still relatively unusual in France, although some formed near Landiras, south of Bordeaux, in 2022.

He said climate change was increasing the frequency of heatwaves and that thunderstorm conditions following three consecutive heatwaves represented a new combination in the region affected by the current wildfire in southwestern France.

Forecasting the storms is difficult because they form directly above fires.

Weather services can predict conditions suitable for thunderstorms, Filippi said, but cannot know exactly where a fire will be burning.

He said unpredictable changes in wind and convection above the blaze in France’s southwestern Gironde region had carried embers farther and created catastrophic local conditions.