In connection with the ongoing giant fires, meteorologists were able to determine last week that the phenomenon had reached France. It is called pyrocumulonimbus, loosely translated as fire thunder cloud - that is, a thunderstorm created by a forest fire.
Very special circumstances are required, which makes pyrocb rare in Europe. Erik Kjellström, professor of climatology at SMHI, says that a survey in 2013-23 found around 760 cases of fire thunder clouds globally.
The vast majority in Canada, the United States, far away in eastern Russia and Mongolia, and in Australia. Those are the three main areas, you could say.
Then it was about one percent, or more precisely eight cases, in Europe.
All of them were far down south.
In Spain, Portugal and Greece.
Extreme winds
Cumulonimbus is the technical term for thunderclouds, while the prefix "pyro-" means that it was created by a fire.
The reason they are feared is the enormous forces they unleash. The heat of the fire chases the steam from burnt vegetation high into the atmosphere. When it cools down there, thunderclouds and extreme winds form. Sparks and embers can thus be spread over long distances - and lightning can start new fires in unexpected places.
Kjellström emphasizes the role of winds.
In the United States, they can give rise to tornadoes and even tornadoes when they are really, really strong.
And in Australia, in connection with the catastrophic fires in the summer of 2019-20, signs were seen that human-caused climate change is exacerbating the problem.
Uncertainty in Europe
Kjellström tells about a study covering southeastern Australia, which compared how favorable the weather and climate were for the formation of pyrocumulonimbus during two 20-year periods, at the end of the 20th century and at the beginning of the 21st century.
There it was seen that there had been approximately twice as many days with favorable conditions.
And future climate simulations pointed to an increase of several more days both during the spring and summer down there.
Whether this means that fire thunder clouds will be able to occur more frequently and further north, even in Europe, is uncertain.
Warmer and drier, that's the conditions there so far, says Erik Kjellström.
But it also requires the “right” conditions in the atmosphere, which means that there remain some question marks for our part of the world.
Since the phenomenon is not that common here in Europe, it is not that well studied either.
