From the Guardian:

One is a boy of 15, who threw a burning cigarette into a wood near Bordeaux. Another is a 36-year-old man who set a paper bag of rubbish on fire in bushes near Perpignan. A third is a 50-year-old woman accused of lighting 17 fires south of La Rochelle.

According to the French interior ministry, since the start of a summer in which a record 115,000 hectares of forest, scrub and heathland have gone up in flames, 514 people – including 198 minors – have been arrested on suspicion of starting wildfires.

Who are they, and what motivates them? Experts say arson is an under-studied field in France. It remains, according to Thierry Toutin, a criminology researcher with the national police, “a mysterious crime, often hard for people to understand”.

Two hundred years ago, under Napoleon, deliberately starting a wildfire in France was a crime so grave it carried an automatic death penalty by guillotine. These days, sentences start at 10 years in jail and a €150,000 fine, rising to 15 years if protected forests or reserves burn, and life if someone is killed.

France’s official statistics classify wildfires by their cause: natural, such as lightning; accidental (say, a vehicle fire or electrical fault); involuntary professional (sparks from a machine); involuntary individual (a cigarette or barbecue) – and voluntary.

In practice, as a government PSA has repeated all summer on radio, TV and online, nine out of 10 fires are caused by human activity, with roughly two-thirds classed as involuntary (which, if negligence is proven, carries a jail term of one to five years).

That means fully one-third of wildfires in France each year are set deliberately, with the intention of doing harm. In 2025, the last year for which full figures are available, deliberate acts of arson were the biggest single cause of forest fires in France, accounting for 29.4% of blazes.

Full story here.

As the final two paragraphs explain, it is not just a third – nine out of ten are caused by human activity. Apart from deliberate arson, the majority of fires are caused by things like cigarettes and BBQs.