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Sixth-generation wildfires: what they are, how climate change affects them and ways to prevent them

Rising temperatures, droughts, heat waves and abundant untreated material in forests are the perfect cocktail for fires to break out. When they are beyond the control of firefighting services - because of their intensity, speed and unpredictability - we speak of mega-fires or sixth generation wildfires, a phenomenon that is not new but whose frequency could increase due to rural abandonment and climate change. Some experts have thus described the fire in Tenerife that began on August 15 and has forced the evacuation or confinement of thousands of people.

18/08/2023 - 16:17 CEST
Update Added statements by Adrián Regos.

Image of the Pinolere neighborhood, in the municipality of La Orotava, which has been evacuated as a result of the proximity of the forest fire that affects several municipalities on the island of Tenerife. EFE/Ramón de la Rocha.

What is a sixth generation wildfire?

Although there is no standard definition, these fires, known as mega-fires outside Spain, are characterised by being extreme in terms of size, behaviour or impact.  

The most common size thresholds are those larger than 10,000 hectares, according to research published in Global Ecolology and Biogeography in which the authors analysed a hundred studies defining this phenomenon.  

"The term 'sixth generation' refers to fires of such intensity that they alter the dynamics of the upper layers of the atmosphere and generate winds that can be very difficult to model, making it impossible to predict fire behaviour. Alongside this factor are other aspects of previous generations," Inazio Martínez de Arano, director of the Mediterranean Regional Office of the European Forest Institute (EFI), tells SMC España.

What are its main features?

As the expert lists, the following factors come together in these fires:  

  • Very high intensity. 
  • Very high speed of propagation. 
  • Long-distance projection of sparks that jump firebreaks. 
  • Simultaneous outbreaks. 
  • Unpredictable behaviour, which exceeds current models.

Can't they be suffocated?

Although many resources are allocated to extinguish them, these fires can spread out of control and exceed the extinguishing capacity, as stated in the report Fire and forest fires in the Mediterranean; a relationship story between forest and society by the Forestry Technology Centre of Catalonia (CTFC). "They cannot be extinguished," stresses Martínez de Arano. "They cannot be extinguished until the weather conditions change," he adds.

They are not extinguishable. They cannot be extinguished until weather conditions change

Inazio Martínez de Arano

The reduction and abandonment of agricultural activities such as grazing in the undergrowth, the extraction of timber and firewood, and the loss of mosaic landscapes with croplands and wooded areas allow for the overgrowth of forests and the increase of forest biomass. This biomass accumulated in the recurrent drought and heat cycles of the summer months acts as fuel and triggers extremely intense fires, which can even jump great distances without vegetation cover.

Is climate change making them more frequent?

"It is causing more days of very high risk and is extending the threatened area," says Martínez de Arano, who adds that, in addition to climate change, another factor that is increasing the frequency of extreme fires is the expansion of the forest due to rural abandonment. 

According to the CTFC report, in many Mediterranean areas this rural abandonment in recent decades has increased the risk of intense fires. This situation is aggravated by climate change and the prolongation of warm periods with drought-like conditions, a situation that increases the risk of fires even in regions and ecosystems not used to such intense fires. 

The sixth synthesis report of the Intergovernmental Panel on Climate Change (IPCC) discusses fires in general and concludes that human factors have most likely increased the risk of compounded extreme events since the 1950s. Such events include fires in some regions. It also highlights that economic impacts attributable to climate change are increasingly affecting people's livelihoods and are causing economic and social impacts beyond national borders, with wildfires as a phenomenon affecting buildings, economic activity and health.

In many Mediterranean areas, rural abandonment in recent decades has increased the risk of intense fires

In addition, according to the IPCC report, with further global warming, regional changes such as increased aridity and fires, heat waves and droughts, even simultaneously in several locations, are expected. Among the main associated risks expected in the short term (with a global warming of 1.5°C), the report highlights the damage caused by forest fires.

What are the characteristics of wildfires in other categories?

A fire generation is defined by a scenario where there is a factor that limits the extinguishing capacity, making it possible for the fire to become a large forest fire, as indicated in the guide Prevention of Large Forest Fires adapted to the Type Fire published by the Generalitat de Catalunya. These generations are marked by the evolution of the landscape according to socio-economic changes and are as follows:

  • First generation: their spread is conditioned by the continuous surface fuel, mainly grassland and bushes resulting from the abandonment of crop fields. The fuel accumulation period is between two and 15 years, they are medium intensity fires, which burn between 1,000 and 5,000 hectares, and the extinguishing measures are based on local and seasonal firefighters. 
  • Second generation: the accumulation of fuel due to the abandonment of crops and traditional agricultural and forestry activity causes faster and more intense fires that spread occasionally with secondary outbreaks. The fuel accumulation period is 10 to 30 years. Their surface area ranges from 5,000 to 10,000 hectares and aerial means are needed to extinguish them. 
  • Third generation: they spread through the treetops at high intensity due to the homogeneity of the forests, as a result of the lack of forest management and the failure to extinguish medium and low intensity fires. The fuel accumulation period is 30 to 50 years. These are fires of 10,000 to 20,000 hectares, with crown fires, convective columns and massive secondary fires over long distances. There are few fire suppression opportunities and rapid behavioural changes that exceed the capacity of fire suppression resources. May occur during heat waves. 
  • Fourth generation: large forest fire that spreads through the forest mass, gardens and houses without difficulties due to the density of vegetation and the continuity of fuel load between the forest area and the built-up area. Simultaneous fires can occur in the same area and can occur during heat waves. There is a shift from attacking fires to defending people and property in a new defensive situation. 
  • Fifth generation: large simultaneous forest fires in risk areas, with extreme, rapid and virulent behaviour, crossing urbanised areas. Simultaneous crown fires appear, with urban and forest interfaces. It exceeds conventional water resources. Coordination between the different fire-fighting bodies and agents is necessary.

What sixth generation fires have there been in Spain? And in other countries?

Adrián Regos, a researcher at the Technological and Forestry Center of Catalonia (CTFC), explained to SMC Spain that the fire in Tenerife that originated on August 15 would be. "The Tenerife fire entered the sixth generation fire category on Saturday afternoon. The conditions of strong winds and low humidity are making extinction work extremely difficult, exceeding the current extinction capacity. These extreme fires are capable of generating their own dynamics and turbulence that favor erratic and unpredictable behavior, which increases their danger," he pointed out.

"As far as extinction is concerned, there is little more that can be done, apart from the enormous task that the extinction systems are already carrying out. It is easy for this fire to exceed 10,000 hectares, thus entering the category of mega-fire, although for their behavior is already an extreme fire", affirmed the expert.

The meteorologist Marta Almarcha, in an article published in, agreed. "The characteristics of the fire in Tenerife lead it to be classified as a sixth generation fire. These fires are characterized by having great intensity, being highly destructive and releasing a large amount of energy, giving rise to their own meteorology within of the fire and what has been seen in the last few hours, the pyrocumulus clouds," she points out. Diana Colomina, coordinator of the WWF forest program, also shared that definition in statements to Infobae.

Previously, the fire in Sierra Bermeja (Málaga), which started in September 2021 and in the extinguishing of which a forest firefighter died, would be classified as a sixth-generation fire. But previously there have been more, as explained to Cristina Montiel, director of the Research Group Geography, Policy and Socioeconomics of Forestry at the Complutense University of Madrid. Twenty-five years ago on the peninsula there were fires of this type in the region of Solsonès and in part of Bages and Segarra, in Catalonia. 

Outside Spain, mega-fires have occurred in recent decades in the United States, Australia, Brazil, the Democratic Republic of Congo and the Russian Federation.

Can they be prevented?

As the CTFC points out, the extent and severity of forest fires are a reflection of the current relationship that we, as a society, have with forests. "The risk can be reduced by addressing the causes of ignition and reducing them to a minimum on very high-risk days," says Martínez de Arano, who adds that the risk of serious damage can also be minimised, although this requires fuel management at the landscape scale and in the forest-urban interface. "It is important to create spaces where fire is extinguishable," he stresses.

Risk can be reduced by addressing the causes of ignition and minimising them on very high risk days

Inazio Martínez de Arano

Eduardo Rojas Briales, in an article published in SMC Spain, also referred to the correct management of the state of forests and the surrounding forest territory in order to prevent fires. "In the long run it will be impossible to tackle fires. The reason? Because their continuity and fuel density will impede the action of extinguishing means, as they exceed by far their technical and personnel safety limits," said Rojas, professor at the Polytechnic University of Valencia, dean of the Official Association of Forestry Engineers and president of PEFC-International. 

The expert recalled the paradox of extinguishing: the more efficient the extinguishing services are, the more they will be able to put out almost all the easy fires, but when the worst circumstances combine, including simultaneity, a few will become catastrophic, which will cause the investment made in extinguishing to be questioned. 

"To bet on extinction is a reactive and insufficient response that only postpones and aggravates the problem," Rojas reiterated. That is why he proposed action on at least three fronts: sufficient public funding, tackling smallholdings and active management.

Are more generations of wildfires expected?

Firstly, in order to avoid ambiguities, some authors propose a homogeneous definition of mega-fire as a mega-fire of more than 10,000 hectares caused by one or more related ignitions. As for new categories of these phenomena, they propose two additional terms: gigafires, for fires larger than 100,000 hectares, and terafires, for fires larger than 1 million hectares.  

"As the Earth's climate and ecosystems change, it is important that scientists can clearly communicate trends in the occurrence of larger and more extreme fires," the authors emphasise in their article in Global Ecolology and Biogeography.

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