France wildfire lightning cloud sparks new fires in Gironde
French officials say a Gironde wildfire formed a pyrocumulonimbus cloud that produced lightning and erratic winds, complicating firefighting.
By Sofia Marchetti · World Affairs Correspondent
3 min read
A France wildfire lightning cloud formed over a major blaze in Gironde, sending bolts to the ground and starting additional fires outside the original burn zone, French officials said. The development matters for firefighters because the fire began producing weather that could shift flames suddenly and make the blaze harder to control.
The Associated Press reported that the wildfire began near Saumos on July 22 and has burned more than 420 square kilometers, or 162 square miles, of forest and scrubland. Officials said it has damaged or destroyed more than 240 homes and forced 220,000 people to evacuate in Gironde.
France’s national firefighters federation said it had not previously recorded the type of fire-generated thundercloud seen over the blaze. The departmental fire and rescue service said the cloud appeared at about 6:20 p.m. Friday, two days after the fire started, weakened overnight as humidity increased, then returned several times.
What is a pyrocumulonimbus cloud?
The cloud is known as a pyrocumulonimbus, or pyroCb: a thunderstorm formed from the heat, smoke and moisture rising from an intense wildfire. Theodore M. Giannaros, a fire meteorologist at the National Observatory of Athens, told AP that it is “a storm cloud born from the intense heat that a wildfire produces.”
Giannaros said a large fire alone is not enough to create one. The atmosphere also must resemble the setup for dry thunderstorms, with very hot and dry air close to the surface and cooler, moister air higher up.
As smoke-filled air climbs from the fire and cools, moisture condenses around ash particles, according to Giannaros. Above the freezing level, droplets turn into ice crystals; their collisions separate electrical charges, producing lightning in the same broad way as a conventional thunderstorm.
Why the cloud makes the Gironde fire more dangerous
Officials said the cloud’s lightning hit the ground and ignited new fires away from the main blaze. Giannaros said the system can also create strong and erratic winds, with rising air drawing winds toward the flames and downdrafts forcing gusts back to the surface.
Those wind shifts can redirect the fire, split it into multiple fronts or push it into new areas, according to Giannaros. He told AP the cloud becomes “its own weather system,” making the fire harder to forecast while it remains above the flames.
Giannaros said fire-generated storms can also produce spinning columns of flame, more often fire whirls than true tornadoes. AP noted that a rarer fire tornado struck Redding, California, during the 2018 Carr Fire, with winds equivalent to an EF-3, killing a fire inspector.
For crews on the ground, the main risk is that escape routes can close as new fires appear beyond personnel and equipment, Giannaros said. In those conditions, direct attack on the flames may become impossible, pushing firefighters toward retreat and community defense.
Why Europe is watching fire storms more closely
AP reported that pyrocumulonimbus clouds have been documented more often in North America and Australia than in Europe. Canada produced a record 142 of them in 2023, while Portugal recorded one during its deadly 2017 fire season.
Europe is warming at roughly twice the global average since the 1980s, according to the EU’s Copernicus Climate Change Service and the World Meteorological Organization. Giannaros said hotter, drier conditions give extreme fires more chances to form pyroCbs, though scientists do not yet have enough long-term data to establish a trend.
The European research project ROSETTA is intended to help fill that data gap, AP reported. Giannaros said the common error is treating the cloud as a byproduct of the fire, when it can influence where the fire goes next.
This story draws on original reporting from Fortune.