Fuelling a Mega Fire

Mega fires don’t evolve without warning. We sow their seeds, watch them grow and are then forced to stand back as they develop beyond the capacity of extinction. 

As the phenomena intensify across the Iberian Peninsula and around the world, leading experts in fire operations and research are urging us to acknowledge the early precursors of extreme wildfires, recognize our role and reevaluate our preconceptions. In order to do so, we must first understand the underlying factors fuelling the severity and scale of modern mega fires.

Fierce and wildly erratic mega fires have become a staple chapter in southern European summers. For the purpose of this report, lacking international consensus on the specifications, we will use the definition of mega fires as those that burn an area of more than 5,000 hectares or emit more than 10,000 kilowatts of energy per square meter. While they cause losses of life, raze thousands of hectares of land, force evacuations and the closures of businesses, the public discourse invariably turns to the point of ignition with arson, negligence, accidents and lightning strikes on trees being the usual culprits.

Beyond its trigger, three critical variables fuel a mega fire: uninterrupted expanses of forest, sewn together by dense, flammable overgrowth and the convergence of unstable atmospheric and climate conditions. These catalysts of continuity, density and weather mean the difference between a fire burning out, and one capable of generating enough momentum to surge across the line of control and into unknown territory.

Mega fires are not a new concept. They have been recorded as far back as 350 million years ago but due to dramatic shifts in our land use and with the accelerant of climate change, they are becoming more frequent, more destructive and affecting new geographic regions. In 2023 Greece suffered the worst fires in European record with more than 94,000 hectares of land burnt in a single event and at least 28 people killed. The deadly Hawaii firestorm in Maui killed 115 people and decimated a whole town. Dwarfing all other countries in 2023 was Canada which lost more than 15 million hectares of land due to mega fires, becoming the largest area burned in its recorded history and more than double the 1995 record. 

The effects of these devastating events are something fire-prone Spain and Portugal understand intimately. In the last 17 years, both countries have cumulatively lost more than 3.1 million hectares of land to wildfires. Some of the most significant events being Spain’s 2022 Sierra de la Culebra fires which destroyed more than 50,255 hectares and Portugal’s record-breaking 2017 season which killed 117 people and destroyed 10% of the country’s forests during the Pedrógão Grande and October fires.

Experts agree one of the most significant causes of mega fires is the expanding continuity of our forests. In the context of mega fire danger, unmanaged and abundant tree areas are an enemy hiding in plain sight. 

As evident from the forest growth map, Spain’s treeline has exploded in growth over the last 30 years while Portugal’s has declined. After huge treeline increases in the second half of the 20th century, experts say Portugal’s forest recovery was delayed by land-use changes together with several fire events after the 1990s which severely scarred the country.

“Contrarily to other European countries and especially Spain, [in Portugal] we don’t see this expansion of forests, what we see clearly is more the loss of agriculture in between forests and shrubland patches, which again reinforce the propensity to have increasingly larger fires”, said Professor Paulo Fernandes, forestry engineer and senior researcher at Portugal’s University of Trás-os-Montes and Alto Douro. But even with the losses and slow regeneration, the country now has more trees than it can manage.

As of 2021, approximately 56% of Spain’s land was covered by forest ecosystems and every year that number grows. Now to reduce fire risk, experts say the country actually needs fewer trees and shrubs. 

Forest continuity is predominantly the fruition of neglected land. After managing and utilizing most of Spain’s forests for thousands of years, the abandonment of agricultural lands and rural towns throughout the mid-20th century facilitated an unfettered expansion of trees. As farming families sought greater employment opportunities with increasing industry in capital cities, trees and shrubs enveloped their fields, blurring parcels of cultivated land into homogenous forests. This relentless reclamation of nature has resulted in expansive forest spaces as well as two of the largest demographic deserts in Europe known as the Spanish Lapland and the Celtic Strip. 

Without interruptions in forest continuity in the form of heterogeneous mosaic landscapes, clearings and agriculture, fires can spread indiscriminately. One of the Peninsula’s most critical cases of fuel continuity can be found in the lower Pyrenees. Forests cover 59% of the mesic mountain range according to the Pyrenean Climate Change Observatory with the most uninterrupted expanses in the central eastern regions. Carbon studies have traced the mountain’s coniferous pine forests back between 50,000-15,000 years. In the past century, however, this resilient forest’s treeline has bulked up and crept to higher altitudes.

Like most forest environments across the Iberian Peninsula, the Pyrenean landscape has undergone multiple land management changes throughout the 19th and 20th centuries. “All forests are an expression of our social and natural history,” said professor, geographer, and author, Dr Martí Boada. The 73-year-old Catalan grew up in the Pre-Pyrenees and has dedicated his life to understanding forests across the Peninsula and the world. Along with his exhaustive research, he has also witnessed firsthand the changes Spain’s forests have undergone in his lifetime. 

“The biggest change is the energy change, when hydrocarbons arrived en masse in the 50s or 60s, it was an energy change. People no longer cooked with charcoal or firewood,” Dr Boada said. “What was previously about 5 tonnes per adult per year in forest consumption, is now 5 butane cylinders, this is key.”

When the forests stopped being utilized, trees reclaimed the space.

The most effective way of seeing the impact a rural exodus has on forest spread is from above. Below is a stretch of land surrounding the municipality of Espinelves in the Pre-Pyrenees photographed aerially between 1954-56 compared with the same area now. 
“In the 60s we in Catalonia had 37% of the surface covered by forest area, and now we are at 72%,” Professor Boada said. That surge in trees has meant a simultaneous increase in the forest’s demand for water.

“If you had about two thousand trees per hectare and now you have more than 20,000, it is as if you had 10 geraniums in your home and you added 100. And you can see this, that is, the river flows have dropped, the aquifers have dropped also,” said Professor Boada. Water stress is one of the leading causes of forest mortality in the Pyrenees which currently sits at around 38%. And the higher the forest mortality, the higher the mega fire danger.

“With this heat, ignitability can come to you in the most unexpected way,” said Professor Boada, “Not only the Pre Pyrenees but all of the Ebro Valley is going to burn.”

It’s a dark prediction but one echoed by other experts too. While fires in the Pyrenees are currently rare, simulations developed by Catalunya’s forest fire service found if a fire were to start under heightened meteorological conditions, it would have the potential to burn through an enormous amount of land based on the current fuel levels.

“So right now we have 3% more chances than we used to have in 2015 of having an event that can support a fire spreading for more than half a million hectares in the Pyrenees, even reaching one million hectares. So that was impossible ten years ago. It started to be possible but rare in 2015, and now there’s a good chance for that to happen. All the elements are ready to cook the recipe, it is just a question of when,” said Marc Castellnou Ribau, Inspector of Catalunya’s internationally recognized Forestry Action Support Group (or GRAF) and a leading expert in fire extinction.

An important role in this transformation can be played by the so-called pyrocumulonimbus: a large cloud originating from the intensity of a fire and similar to those generated by volcanic eruptions. The mass of warm air made of water vapor and ash, rises at high speeds and condenses when it meets a cooler environment. Pyrocumulonimbus clouds can cause thunderstorms and electrical activity. They are capable of generating bursts of rain and spreading small particles of ignited matter through the air, to create new fronts or secondary fires.

If a fire did start in the Pyrenees under high fire danger conditions the simulations predict it wouldn’t take long to develop into a mega fire. “It needs one day to start and build pyroconvection, one long night where the pyroconvection is maintained and the second day when it finally blows up. That’s the process,” he said. 

“There is a lot of evidence of mountain areas around the world going through the same process and the Pyrenees are no different,” said Castellnou. The region has become his team’s most critical focus area. “It is where the big fire can happen and where the most efforts to convince society that we must manage the landscape is,” he said. 

Professor Graciela Gil-Romera is an expert in fire paleoecology at the Pyrenean Institute of Ecology, a research center within the Spanish National Research Council. She agrees the current forest spread in the Pyrenees creates a very dangerous situation. “Having such continuity of fuel in the scenario of global warming, that’s a bomb,” She said, “Sometimes you have the urban forest boundary mixing with the wilderness and that’s when the critical thing happens. Because then you may have a fire start which might not be intentional and then it spreads with no end, and there’s nothing, no means that can stop the fire.”  

Wedged in by this prospective fire fuel are the small rural towns and urbanizations dotted across the mountain range. Their residents will find themselves in the eye of the storm should a mega fire ignite, something that deeply concerns Marc Castellnou. He sees new homes continually built in the path of future fires.

“The population is living calmly on a Mediterranean coast or in a boreal forest because they think a devastating fire cannot happen because the extinction systems have been saying they can put out the fires. But we are not explaining the whole truth. We can no longer put out those fires,” said Castellnou. “We are not prepared [for mega fires], although we have been warned.”

Wrangling continuity is an endless battle against nature’s unrelenting growth but it is also a result of fast and effective firefighting operations. This concept is known as the fire paradox because the success and efficiency of extinction operations over decades has directly contributed to an increase in the fuel continuity and therefore fire danger.

Periodic fires are a necessary part of nature, helping to manage biomass growth, cycle nutrients, and evolve species. Without it, the ecological balance is lost, there is no fire adaptation and therefore more chances of suffering large destructive fires. Unlike surface level prescribed burns or small grass fires, mega fires damage plant tissue and cause long-term scarring, delaying landscape recovery due to their intensity. This paradox has led to calls for a shift in focus from solely reactive extinction operations to proactive fuel management. 

“We need to think that fire is part of our ecosystems in the Mediterranean forests. We have to live with fires and we can, through management, decide how they occur,” said Sergio de Miguel, Associate Professor of the University of Lleida and researcher of global forest ecosystems. 

If this change was realized it would also be a significant cost-saving measure. “Why? Because we respond, not to what is burning but to what could burn,” said Marc Castellnou Ribau. He says current firefighting operations cost about 20,000 euros per hectare, while the average cost of managing a hectare of land is between 2,000-3,000 euros.

Knotted within the forest walls is the second variable fuelling mega fires: density. That is the vertical and horizontal build-up of vegetation undergrowth which acts as a ladder during a fire, capable of distributing fire to other trees and rapidly lifting flames from the forest floor up to the canopy. A forest’s mass of ladder fuels will determine how hot a fire will burn and how fast it can travel. To get a rough idea of how dangerous the fuel load of an area is, forest engineers use a simple rule of thumb: If a square meter of land holds more than a kilogram of dry litter or shrub, that indicates it could burn at 10,000 kilowatts per meter, equivalent to the magnitude of a fire which can not be fought. If you wander off the path through a forest can you walk among the trees? In the below video you can see that walking through the dense and dry branches is almost impossible. If a fire were to start in this Las Hurdes forest it could easily evolve into a mega fire due to the amount of dry fuel available to burn.

At its heart forest density is an absence or failure of fuel management. Throughout the Iberian Peninsula we find extensive areas with high vegetation density. Portugal’s central region is the country’s most dense and a key example of how good and bad forest management is capable of affecting fire behavior.

“That’s the big problem with these large, very continuous, very dense forest patches that are so characteristic of central Portugal. It began by being planted, supposedly it would have to be managed in an orderly manner, but it has become a certain jungle, so to speak, of trees of various sizes and heights, but always in great density and therefore enhancing extremely intense fires,” said Professor Paulo Fernandes of the University of Trás-os-Montes and Alto Douro, one of the most cited experts on fire science ecology in Portugal.

He believes the region suffers under the weight of so much forest mass mostly due to a lack of clearing on the part of small private landowners. “The soils are not at all good for agriculture and the use of forestry from the mid-20th century became, let’s say, the obvious option or the only option in terms of economic income for the population. The entire area was initially forested with pine and later with eucalyptus. The problem is that in these plantations, especially after fires, the intensity of the management is generally very reduced,” he said.

Portugal has ranked 7th in the top 10 countries with the highest proportion of forests under private ownership accounting for about 95-97% of the territory’s total forest area (much like the neighboring Spanish province of Galicia.) Most of these properties cover less than 0.5 hectares of land however many of their owners are still unable physically or economically to actively manage their fuels.

“In Portugal, there’s a saying that the owner of the forest only touches it when his daughter gets married and he cuts down the pines to pay for the wedding expenses. It’s a caricature, but it is a bit like that,” Prof. Fernandes said.

“There is no forest management and, in many situations, there is no professional management. When there is some, it is in forests managed by companies. These types of forests or plantations are inherently vulnerable to fire due to the accumulation of biomass by the species that are used, which are normally fast growing like pines or really fast like eucalyptus.”

The invasive Australian tree species are popularly used for plantations across the Iberian Peninsula leading them to shoulder, what experts say is, a disproportionate share of the blame when it comes to fire danger. “The blame is always attributed to eucalyptus, but we know that this is widespread. It could be eucalyptus, it could be pine, it could be cork oak or it could simply be shrubby areas,” said Professor Fernandes. The key is in the management or lack thereof and one of the largest issues contributing to forest fires in Portugal are abandoned plantations. With the amount of trees in the region, it is virtually impossible to keep on top of the growth. 

Dina Duarte has spent her whole life in the small town of Castanheira de Pêra, in the Leiria district of Central Portugal. The town is home to just 2,645 people living boxed-in by thick, unmanaged acacia, pine and eucalyptus trees, many of which meet in canopies over small roads and grow right up to the front doors of homes. 

“When I was little, I realized I had to be prepared to deal with this for the rest of my life. I’m aware when the heat arrives there’s always the possibility fires will happen,” Duarte said.

After the fire, Dina began working with the Association of Victims of the Fire of Pedrógão Grande, of which she is now president. Her work focuses on advocacy and education, particularly for the aging and declining rural population. “I believe the June 17th fire came to create awareness and wake us up to this new reality. We have to do something different. We have to apply laws so that the populations living in their villages, and there are fewer and fewer of us, can live safely close to nature.”

Working to help others adjust to the new reality is the University of Porto’s Professor Fantina Tedim, co-author of Extreme Wildfire Events and Disasters: Root Causes and New Management Strategies. When it comes to controlling Portugal’s forest density, Professor Tedim is a realist. 

“Portugal doesn’t have the human or financial resources to carry out all the fuel management, so it’s important to pay attention to the places where it is strategic to do this management to avoid the occurrence or influence [on] the behavior of the fire.” Though she has witnessed some changes in Portugal’s fuel management policies since the 2017 mega fires, such as new clearing obligations around homes and towns, she says a one size fits all approach will not work. “The reality is much more complex. If we are faced with a eucalyptus forest, a pine forest or an oak forest, the fuel management must be done differently.”

In Spain similar examples of worrying forest density can also be found. In the province of Extremadura many farms and olive groves have been left abandoned due to a drop in profitability and the toll of labor. Jesús Campo García is among those who have walked away from their plots. The 72 year-old has spent his life in and around Monfragüe National Park in the municipality of Serradilla working as both a forest agent and an olive farmer.

“There is nothing managed here in La Solana other than a few farms right next to the road, they are the only ones. Everything else is completely lost, everything,” he said. During his 25 years working as a local forest agent, he witnessed the landscape change, the shrubs build up and the fires intensify.

Aiding in the crowding of forests has been the gradual tightening of important conservation regulations on natural spaces, especially in Spain. The environmental protections needed to preserve biodiversity and habitats have been strengthening since the second half of the 20th century. In Portugal, 22.4% of the land is defined as ‘protected areas’ and in Spain 28%. Many form part of a chain of European forests known as the Natura 2000 Network and their protections mean that to preserve the native plants and wildlife, limitations are enforced on the ability to manage the fuel buildup, carve fire breaks, and perform prescribed burns. That’s why in some parts of the Peninsula, largely in Spain, experts are concerned the restrictions risk endangering the subjects they were created to protect.

In the 2022 fire season, 42% of the total razed land in Spain was within Natura 2000 sites, with the Sierra de la Culebra in Zamora, Alto Palancia in Bejis, and Serra do Courel in Galicia the worst affected. In Portugal, 37% of the fires were in protected Natura 2000 sites, with the worst affected in the Serra da Estrela Nature Park and the Alvão Natural Park. This follows a trend in recent years where protected areas appear to be having an increasing vulnerability to fires. In Portugal protected areas pose less of a problem, due to more relaxed clearing policies allowing an easier balance between nature and people. 

In Spain, fires within the Natura 2000 Network have been found to be on average twice as destructive as those originating outside, according to the Spanish Government’s Los incendios en la Red Natura 2000 report. “There are two take-home messages here. One is that protected areas are not protected against fire, they do burn, so fire prevention must happen there and in some areas, we see protected areas burning more than they should based on the area they occupy,” said scientist and forest engineer, Professor Victor Resco de Dios, of the University of Lleida who co-authored a study into the drivers of 2022’s fires.

In Spain some families who live in or near protected areas say the overly prescriptive rules surrounding the clearing of fuel are leading to fears a lack of management will promote larger wildfires. Carlos Grande Muñoz helps his brother run a sheep and cattle farm in Miravete, bordering the protected area of Monfragüe National Park. Their family felt the effects of the July 2022 fire which swept through their property killing 35 of their sheep and a horse.

“Well, the situation here in Extremadura on that date, as every summer, was very complicated due to the heat, the high temperatures, the very dangerous windy days, and those of us who live here know a little of what can happen, but not the magnitude it had,” said the 37-year-old.

Carlos is one of many local landowners who feel there are no incentives to keep land managed. He says there are disincentives given the risk of large fines for disturbing wildlife habitat and the amount of paperwork needed for works to be approved. “They put so many obstacles in your way that in the end you lose your desire, you lose your enthusiasm and you don’t do anything, I’d rather throw in the towel, so what happens is that these areas are really depopulating with livestock and people, because there’s no help at all, on the contrary, there’s nothing but problems.”

Some of the most significant precursors to mega fires are impossible for us to see but essential for us to understand. Humidity, wind and increasing temperatures are among them. 

The relationship between vegetation and its access to water both through the earth and the atmosphere is directly influencing flammability and therefore mega fire risk at all times. When temperatures are high and relative humidity is low, plants want to retain as much of their water as possible, so they have to choose between growing or surviving. In either case, they are left with a lower moisture content and as a result burn faster. 

This video illustrates the difference in burning speed and intensity between two samples of pine (Pinus pinea). The fuel moisture content of the branch on the left is dry at only 23% moisture content and the branch on the right has a lot of moisture inside, at 162%.

Researcher Javier Madrigal, senior scientist at the Institute of Forestry Sciences (ICIFOR-INIA, CSIC) and associate professor at the Polytechnic University of Madrid (UPM), conducted this experiment for SONDA. He says a plant’s flammability is partly determined by its characteristics, such as thickness, however, it will mostly be influenced by the amount of water the plant has inside of it. “That doesn’t mean to say that a wet tree does not burn, because if there is a lot of energy everything will be lost, but it gives us an idea of the ease with which one process can occur with respect to another.”

In the long term, dry weather and a lack of rainfall translates to drought. The Iberian Peninsula periodically suffers long stretches without sufficient rainfall. For Spain in particular, the drought of 2019 – 2023 could have a lasting effect on mega fire danger.

“All climate models say that it will last for decades because it is not only a temporary drought, but a global circulation change, so we will see a total change of our landscape in the coming decades because we are changing the water regime,” said Marc Castellnou Ribau.

Seizing on parched and dead fuels are dry lightning storms. Fires started by lightning only account for a small percentage of total fires in Spain and Portugal but they are increasing in frequency and burning larger areas of land. That’s believed to be because they can ignite during a moment of heightened atmospheric instability often in densely forested areas away from high surveillance and are capable of igniting multiple fires simultaneously.

“When a fire occurs in those [dry lightning] conditions what it really does in the atmosphere is throw the flame front literally upwards, it draws the flame front towards itself and accelerates the combustion process,” said Madrigal.

Back on land, topography also plays a big role in determining mega fire direction and intensity. If an area is inaccessible to people or machines, not only will the fuel be unmanaged but when a fire starts it can’t be controlled. The formation of the land itself also has the potential to shape the fire’s progression, influencing direction through the aspect and degree of slope and the creation of wind channels. 
Accelerating and exacerbating these factors is climate change. Not only is human-caused climate change helping to lengthen the fire season, it’s also increasing the frequency and intensity of mega fires, adding an additional time pressure to a problem already overtaking us. Professor Tiago Oliveira, president of the Portuguese Agency for the Integrated Management of Rural Fires (AGIF), describes the challenge as one without a hero. “Do you know any hero the world recognized because he prevented an event that didn’t occur? It’s not popular, so we are facing a dilemma here. We know how to do it, [prevent fires] the money is flowing in the proper direction, but we are not doing it as fast as it is needed.”

“There is a joke people who work in these types of phenomena use. It’s that a guy is jumping from the 10th floor and he is skydiving to the ground and on the second floor, he says, “So far, so good.” It’s a dark joke but it describes a little bit of what we are envisioning.”

Director: Mikel Konate | Text: Lily Mayers | Video: Mikel Konate and Pablo Tosco | Photography: Paulo Nunes dos Santos, Mikel Konate, Lorena Sopena, João Porfírio and Santi Palacios | Design and illustration: Jorge Mileto | Text editing: Maribel Izcue | Data analysis and visualization: Javi Aparicio | Web development: Full Circle | Production: Sonda International

This report has taken ten months to compile. It has involved interviews with more than 20 people including local residents, forest engineers, professors, authors, firefighters, and fire analysts. We drove thousands of kilometers across Spain and Portugal and walked through countless forest landscapes to understand the issue firsthand.  

While this sort of in-depth journalism is vital to our societies now more than ever, it is not lucrative nor sustainable without support from our readers. 

Sonda Internacional would especially like to thank Víctor Resco de Dios, Marc Castellnou, Isa Vázquez and Javier Madrigal for their advice and support in the making of this report.

The Fuelling a Mega Fire report forms part of the larger Mega Fires: Beyond Extinction project, a major undertaking only possible thanks to the collaboration of experts and, above all, the community of members who support us in making visual journalism on the climate crisis. 

You can see other chapters within the report here and watch our Conversaciones series bringing together firefighting, forest engineers, and climate experts here. 

The project is well underway, but we need more help to complete it. 
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