The mega-fires striking France and Spain have astonished observers both for their scale and their ferocity. Numerous firefighters have described unprecedented situations — flames capable of spreading at extraordinary speed, and in some cases a complete inability to tackle the fire front. So what makes these blazes so dangerous and difficult to contain?

Sixth-generation wildfires: the most violent and uncontrollable

Spanish Prime Minister Pedro Sánchez, commenting to the press on events in recent days, explained: "What we are experiencing is not a succession of isolated events. It is the most painful expression of the climate emergency, which is making sixth-generation wildfires more ferocious, heatwaves more frequent and our territory more vulnerable." It is precisely the presence of this type of blaze — fuelled and exacerbated by global warming — that is alarming experts.

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Those classified as "sixth generation" represent the most extreme and most uncontrollable category in the wildfire classification system. "Many of the fires recorded in the summer of 2021 in the eastern Mediterranean region, and particularly in Turkey," explains Vittorio Leone of the Italian Academy of Forest Sciences in a study titled "New-generation wildfires and the need to change the extinction paradigm," "showed very high Fire Radiative Power values, detected by the Sentinel-3A satellite." This value "measures in megawatts (MW) the energy globally emitted by a fire."

Fuel, propagation, intensity: the characteristics of extreme wildfires

The expert notes that, during that year, some blazes recorded Fire Radiative Power values high enough to be classified as "sixth-generation fires: pyroconvective phenomena, or firestorms, characterised by continuous fuel loads, high propagation speed, extreme intensity, occurring with simultaneous action in wildland-urban interface zones, and covering an area large enough to fall within the megafire category (for the European Union the threshold is at least 500 hectares)."

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According to the "generation" classification system, fires from the first to the third category are low-energy blazes, manageable by firefighters using ground-based equipment. Fourth- and fifth-generation fires, by contrast, involve a significant increase in both extent and propagation capacity and are often linked to extreme, prolonged heatwaves. They therefore require additional resources, particularly aircraft.

The ability to generate their own local "weather systems"

Sixth-generation fires, as the name suggests, display an even greater energy intensity, propagation speeds of up to thousands of hectares per hour and, in some cases, the capacity to generate their own local "weather systems". They produce dense, towering clouds known as pyrocumulonimbus, which can in turn trigger thunderstorms with lightning that further feeds the fires, along with winds shifting in unpredictable directions that render the flames impossible to control.

Alongside the "generation" classification, Leone also cites other possible quantitative parameters, according to which one may speak of "extreme wildfire events (Extreme Wildfire Event, or EWE): pyroconvective events with an intensity (expressed in kilowatts per metre of fire front) greater than or equal to 10,000, a propagation speed greater than or equal to 3 kilometres per hour, and a distance of more than one kilometre for the ignition of secondary fires via spotting phenomena."

Beyond classifications, the expert underlines that "the characterisation of many fires as sixth generation is particularly alarming, since it is estimated that phenomena of this type, though numerically a small proportion (10 per cent of the total), are capable of causing 90 per cent of overall damage, according to a 2020 World Bank analysis." This is because they "exceed the internationally recognised containment capacity, defined as a maximum intensity of 10,000 kW per metre of fire front."

The complex and delicate solution: firebreaks

And given that sixth-generation wildfires will become increasingly frequent as a result of the climate crisis, "it is reasonable to ask whether the fire defence system in rural areas available to most countries is sufficient to ensure safety from wildfires in general, and from extreme ones in particular. The answer is, unfortunately, no."

It is therefore necessary to rethink intervention methods as well. Often the only solution for tackling fires of such magnitude lies in so-called "firebreaks": strips of land from which vegetation is removed either by clearing it entirely or by burning it in advance. These are, in any case, complex and delicate operations that require great caution and the involvement of trained professionals.