PARIS: French officials said a wildfire in southwestern France became so powerful that its smoke became a hurricane, sparking lightning that struck the ground and sparking new fires beyond the original blaze.To put it another way, this meant that Hell was no longer solely driven by weather. It was creating its own. The thunder clouds also produced violent, erratic winds that were capable of carrying the flames in new directions.This phenomenon, called pyrocumulonimbus or pyroCb, is rare in Europe and more commonly documented in North America and Australia, where it occurs only in some of the most severe fires. France’s national firefighters federation said it had never recorded a similar case in the country before.The fire broke out on July 22 near Soumos and has since burned more than 420 square kilometers (162 sq mi) of forest and bush, damaged or destroyed more than 240 homes and forced the evacuation of 220,000 people in the Gironde.Two days after the fire broke out, at around 6:20 pm on Friday, the Departmental Fire and Rescue Service said it had generated pyrocumulonimbus. Due to increased humidity, the clouds weakened overnight, then formed again several times.
an electrified black thunder cloud
Again and again, the heat and smoke rose upward into a vast black cloud, electrified and illuminated from within.“Imagine a campfire that is so big and hot that the smoke from it turns into a storm-like cloud,” said Theodore M. Giannaros, a fire meteorologist at the National Observatory of Athens.“That’s a pyrocb – a storm cloud created by the intense heat generated by a wildfire.”It takes more time than a big fire.There is no set temperature at which one is formed, Gianaros said; What is needed is the kind of environment that produces dry storms – very hot, very dry air near the ground, with cool and moist air above.Hot air filled with smoke and moisture then rises rapidly above the flames. As it rises and cools, water vapor condenses around the ash particles.Above the freezing point, the droplets become ice crystals whose collisions cause separation of electrical charges, as occurs in a normal thunderstorm.
Lightning strikes and more destruction follow.
Beneath this storm lies a landscape that is already ready to burn. The cloud then magnifies the disaster that caused it.Updrafts pull powerful winds toward the fire, while downdrafts push gusts back to the surface.Those changes can divert the flames, split them into multiple fronts or send them running in a new direction.“It’s a feedback loop, not a one-way effect,” Gianaros said. “Once it forms, the cloud becomes its own weather system, sitting above the fire and becoming harder to predict.”The system can also spin whirling columns of flame – typically fire whirls, which Gianaros describes as dust devils made of fire and heat rather than dust.True tornadoes are rare, although a tornado struck Redding, California with winds equivalent to an EF-3 during the 2018 Carr Fire, killing a fire inspector.For firefighters, escape routes may close without warning as fresh outbreaks appear outside their crews and equipment.A direct attack may be impossible, forcing crews to retreat and defend communities.The danger, Gianaros said, is that the fire is spreading faster than evacuation arrangements can be made.Until now, pyrocubes have been primarily an Australian and North American phenomenon. Canada alone will produce a record 142 in 2023.
In Europe, pyroCBs are rare.
Portugal set a record during its deadly 2017 fire season. Now France has also been included in this list.According to the European Union’s Copernicus Climate Change Service and the World Meteorological Organization, the continent is warming faster than any other continent on Earth – almost twice the global average since the 1980s – with heat waves becoming more frequent and severe and drought spreading across the south, turning forests into fuel.Hotter and drier conditions create a greater opportunity for extreme fires, Gianaros said, but scientists still lack enough long-term data to establish a trend.The European research project Rosetta aims to bridge that gap.The most common misconception, he said, is that clouds are just a side effect. As long as it hangs above the flames, it helps determine where the fire will go next.