Firefighters couldn’t believe their eyes. “We had never seen anything like it. A cloud formed that multiplied the fire, hurling flames kilometres away.” It happened on July 24, 2009, in the Els Ports Natural Park in Tarragona, Spain. The fierce wildfire, which burned about 1,140 hectares, left firefighting teams baffled: the situation shifted up to five times in just a few hours, defying all weather forecasts. Erratic winds turned into a deadly trap that claimed the lives of five firefighters caught in the flames. That disaster didn’t fit into any of the existing models; over time, it became a reference point for what Europe today calls a “sixth-generation wildfire.”

This past summer in the Northern Hemisphere has sharpened the profile of this new type of fire. According to the Copernicus European Forest Fire Information System (EFFIS), around 678,000 hectares burned in the western half of the Iberian Peninsula —403,000 in Spain and 275,000 in Portugal. Most of these fires have now been officially classified as sixth-generation: blazes of extreme virulence that force a complete rethink of both firefighting methods and prevention strategies.

What sets these fires apart is not only their size, but also their ability to create their own atmospheric dynamics. In several of the major blazes this summer, firefighting crews observed the same phenomenon described by firefighters in Horta de Sant Joan in 2009: the formation of towering clouds—so-called pyrocumulus—that resemble the stormy cumulonimbus.

These massive convective plumes, until recently associated almost exclusively with volcanic eruptions—where the term was coined—operate under very different drivers. Whereas in cumulonimbus clouds it is water vapour that rises, condenses, and ultimately falls as rain, in pyrocumulus it is extreme heat that propels ash, embers, and smoke, generating violent updrafts, erratic winds, and even lightning. The cloud ceases to be a mere by-product of the fire and becomes a generator of fire itself, with movements that defy prediction.

It is the hallmark of sixth-generation wildfires: they do not merely consume forest mass, but evolve into autonomous meteorological engines that overwhelm any forecast and multiply ignition points at random. Their ferocity is such that, beyond the vegetation cover, they devastate entire towns and force mass evacuations.

To understand the qualitative leap from fifth- to sixth-generation wildfires, it is useful to review the typology defined by experts in recent decades. The following table—designed as a quick reference—summarises knowledge that should be shared with the public:

• First Generation
  Rural fires in agricultural areas or sparse forests. Easy to control with ground crews, aided by the discontinuous fuel they encounter. Their environmental and social impact is minimal.
• Second Generation
  Burn in denser forest stands, which means a greater fuel load. They require aerial firefighting resources and affect more complex ecosystems.
• Third Generation
  Spread into wildland–urban interface zones, posing an evident risk to people and property. Beyond aerial resources, they demand strong coordination between wildland and municipal firefighters. They have a significant impact on public opinion and the media.
• Fourth Generation
  Break out in large, continuous forest masses. Fire behaviour becomes self-sustaining, with rapid rates of spread. They require intensive aerial action and careful strategic planning. These fires can last for weeks.
• Fifth Generation
  It can be seen as a combination of third- and fourth-generation fires. They break out simultaneously on multiple fronts, overwhelming firefighting capacity. Crisis management becomes essential, involving all levels of government—local, regional, and national.
• Sixth Generation
  These are extreme fires. They generate their own weather (pyrocumulus), making them unpredictable and erratic. Their extinction is beyond human capability and depends instead on favourable shifts in humidity, heat, and wind. They represent a high risk to firefighters and the population, with massive ecological, economic, and social impacts.

Statistics show that in recent years, wildfires have not only consumed forests in the subtropical belt: roughly 70% of all tree cover lost to fires over the past two decades has occurred in the continental belt surrounding the Arctic, in the so-called boreal regions. Here lies the taiga, the largest terrestrial biome in the world: it accounts for about 30% of global forest area and stores more surface freshwater than any other ecosystem. This forest, composed mainly of conifers—pines and firs—along with deciduous species such as aspens and birches, stretches across eight countries: Canada, China, Finland, Japan, Norway, Russia, Sweden, and the United States.

The connection to heatwaves and droughts is clear. In Russia, the large fires of 2021 coincided with prolonged periods of anomalous temperatures. In Canada, 2023 marked the worst record of burned area: 9.5 million hectares of forest—roughly the size of Portugal—went up in flames after months of drought from January to July, with record temperatures exceeding 40 °C in many areas.

Traditionally, wetlands experience exceptionally dry periods. While the boreal forest accounts for the largest historically burned areas, other green lungs of the planet are not spared. Amazonian, Central African, and Indonesian forests, despite their high humidity, are increasingly suffering the impact of fires coinciding with altered rainfall patterns.

The global proliferation of wildfires cannot be understood without the backdrop of climate change. The combination of heatwaves with record-breaking temperatures and structural drought that dries out vegetation acts as the perfect trigger, allowing fires to ignite easily and spread with unprecedented intensity.

Reports from the Spanish State Meteorological Agency (AEMET) and the Intergovernmental Panel on Climate Change (IPCC) both highlight that the Mediterranean region is one of the planet’s critical hotspots: here, warming is advancing 20% faster than the global average. This translates into longer fire seasons, drier soils, lower atmospheric humidity, and increasingly stressed vegetation.

Preventing wildfires does not rely solely on firefighting resources—it depends on how land is managed. In Spain, the problem is evident in depopulated rural areas where forests have been abandoned.

Traditional agroforestry practices, which combine crops, trees, and shrubs on the same land, and silvopasture, which integrate trees, pastures, and livestock, act as natural firebreaks by preventing the uncontrolled accumulation of biomass. Depopulation also means less surveillance, less forest maintenance, and reduced local response capacity.

When forests are abandoned, nature reclaims its space, and the understory becomes dense with vegetation—a positive outcome ecologically, but disastrous for fire propagation. In these conditions, a paradox emerges—as seen this year in the Iberian Peninsula—where abundant spring rains promote vegetation growth that, once dried in summer, becomes fuel for the flames.

Land management, which is also crucial for flood prevention, becomes essential. It is a complex challenge, requiring a high level of socio-political collaboration. Still, it is unavoidable if society wants to live with a risk that has shifted from exceptional to structural.