On the afternoon of June 17, 2017, numerous fires broke out in Portugal. One of these, near Pedrogáõ Grande, burnt for almost a week, at the crazy rate of over 20,000 hectares of pine and eucalyptus forests devoured every day. 66 people died, 250 were injured and more than double that number lost their homes. It was one of the most violent forest fires in Europe in the last century, but it was not an isolated case. Fires with extreme behaviour – totally out of scale with respect to the historical series of the regions they hit and virtually unpredictable and unstoppable – are in fact becoming more intense and frequent. In Europe, the Mediterranean regions are confirmed among the most vulnerable on a global level, while other areas much further north on the continent, with the climate crisis advancing, are finding themselves exposed to the risks of fire.

Growing impact

It seems almost intuitive that, in a warming world, the risk of fires is growing. The proportions of the phenomenon are less so: according to a recent study published in Nature Ecology, the frequency of the largest and most virulent fires has more than doubled in the last 20 years, at a rate that continues to accelerate: 6 of the seven most serious have occurred in the last 7 years.

The impact is devastating for both society and ecosystems. It is estimated that the dust generated by the Indonesian fires of 2015, for example, contributed to the deaths of over 100,000 people. The Australian fires of 2019, on the other hand, are said to have killed almost 3 billion vertebrates, almost entirely erasing the range of over 100 species. By destroying the main storage tanks of CO2 – the forests – extreme fires also exacerbate climate change.

The problem is global, but not homogeneous. While the humid tropical regions do not see significant increases, the phenomenon has grown dramatically in several areas including Australia, and the very wide band that crosses the boreal coniferous forests, from Siberia to North America (the case of the Canadian fires of June 2023, which painted the sky of New York red for days, is emblematic).

Among the most affected biomes, the warm-temperate forests and the Mediterranean scrub stand out. It is no coincidence that, in July 2018, Greece saw the second most lethal series of forest fires of the 21st century (104 victims in 3 days), second only to the Australian “Black Saturday Bushfires” that killed 173 people in 2009. In Europe, over the last 50 years, the territories that have seen weather conditions favourable to fires (represented by indices such as the FWI, Fire Weather Index) have more than doubled.

Big, small, deadly, catastrophic: fires are not all the same

Of the many hundreds of thousands of fires that occur every year on Earth, most are small, extinguish spontaneously or are quickly put out. Fire can also bring ecological benefits and, in some cases, is started in a planned manner.

A significant and counterintuitive fact is that, globally, the number of fires does not appear to be increasing; indeed, both due to economic and social changes and thanks to progress in control techniques, it is actually decreasing. This apparent paradox can lead to underestimating or even hiding the risk of large and uncontrolled fires, which is instead increasing sharply.

To put things in order, we must consider that the term “fire” includes extremely different phenomena, starting with the size, which can vary from a few handfuls of square metres to hundreds of thousands of hectares. All levels of the forest can burn, from the ground to the canopy (generalised blaze), and this is the most serious case, but sometimes the flames only affect the undergrowth, or even just the ground. Focusing on damage, victims and even trauma to those affected is essential, but stopping there would risk confusing the intrinsic gravity of the event with possible negligence and other social aspects of management.

Sometimes experts use specific terms (conflagrations, blow-ups, megafires) for fires that behave particularly violently or that suddenly change their features, further putting firefighters and civil protection in difficulty.

Extreme fires: it’s not just a matter of size

To frame the phenomenon as objectively as possible, scholars have coined another specific term: Extreme wildfire event (EWE). Extreme fires are those that are technically impossible to contain, at least in the most acute phases, and so rapid and aggressive that accurately predicting their evolution is virtually impossible, even with the best technologies.

What makes a fire extreme is not necessarily its size: if a fire of 10,000 hectares occurs in the immensity of the Australian bush or in the woods of a European country the effects are very different. Today we therefore tend to reason relatively, comparing them with the historical data of each region and identifying those that are “off scale”.

An EWE, however, is “extreme” above all for its behaviour. To promptly assess whether this is the scenario that rescuers are facing, today the tendency  is to focus on easily detectable characteristics, such as intensity (amount of heat released at the front of the fire, the threshold of which can be set at 10,000 watts/metre), the height of the flames (greater than 10 metres) and a propagation speed that exceeds 100 metres per minute. An important role is also played by the presence or absence of the ability of a fire to “reproduce” driven by wind and heat (spotting), which in an EWE can occur several kilometres away.

Fires and atmosphere

The interaction with the atmosphere, or pyroconvection, is almost always at the basis of extreme behaviour. Heat causes smoke, hot air and huge quantities of steam to rise, which then, once they reach a certain altitude, condense, forming clouds (pyrocumulus and pyrocumulonimbus), capable of triggering storms and strong winds, while aerosols can reach the limits of the stratosphere, like some volcanic eruptions, and spread on a global scale.

These phenomena can not only further strengthen fires, but also make them so unpredictable – given the chaotic nature of the atmosphere – that today not even a supercomputer, in hours of work, can process simulations that go beyond a handful of minutes.

With climate change, which increases humidity and instability of the atmosphere, pyroconvection becomes more frequent. However, the climate crisis also affects other aspects: first of all, frequent droughts prolong the dry season (or fire season) in which vegetation is particularly flammable. Even in other seasons, however, plants can enter a state of stress that makes them more vulnerable.

A new geography of fires

In the last 30 years, almost 80% of the European surface affected by fires was in Mediterranean countries. However, fire is increasingly moving north: in 2018 and 2022, temperate and boreal forests accounted for almost half of the affected territories.

Fire-Res researchers have compiled a database of extreme fires that occurred in Europe between 2000 and 2022, identified by Fire-Res researchers on the basis of EFFIS (European Forest Fire Information System) data. Extreme fires in terms of size (over 7,400 hectares, the threshold below which 99.9% of the continent’s fires fall) were 109: 44 in Portugal alone, 35 in Spain, 18 in Greece, 6 in Italy.

In central and northern Europe, fires almost never reach dimensions comparable to those in Mediterranean countries, but episodes that are out of scale in terms of behaviour and size are rapidly increasing. During the exceptional heat wave of 2018, for example, a series of exceptional fires forced Sweden to ask for help from the international community.

Climate unknowns

The European areas exposed to weather conditions favourable to fires have already doubled  in the last 50 years, going from 20% in 1971 to 40% in 2021. To look to the future, the Fire-Res researchers have tried to evaluate the evolution of the same parametres according to the different scenarios of worsening of the climate crisis hypothesised by the IPCC (Intergovernmental Panel on Climate Change).

Even in the most optimistic hypothesis, with low emissions and less than 2 degrees of warming, in the next 15 years parametres such as the FWI (Fire Weather Index) will increase further in central-southern Europe, especially in the Iberian Peninsula and the Balkan countries. In the most pessimistic scenarios, “fire weather” expands across almost the entire continent, with the exception of Scandinavia, and the greatest increase shifts to the north and east, with a peak in the internal and eastern areas of the Balkan Peninsula (especially Bulgaria, Serbia, North Macedonia, Romania).

Whatever scenario occurs, it is now clear that the boundary between the territories where large and extreme fires are already a clear threat and those where they are not yet is increasingly blurred. In a rapidly changing planet, proceeding with the tools of the past – simply trying to put out the fire at all costs – is no longer enough. A deeper paradigm shift is needed, which begins with a thorough rethinking of our relationship with the territory.

Fire-Res is a European Horizon2020 project working to build a more resilient Europe against the growing threat of extreme wildfires. If you want to stay informed about these phenomena, discover prevention strategies and best practices, subscribe to our newsletter