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Wildfires have been a source of fear for many people as these great infernos blazed through Brazil, California and Australia in recent months. But what has caused the rise in such destructive power and what are we doing about it?
Wildfires are large fires that spread quickly and are out of control in wild landscapes. They start in one of two ways: naturally or at the hands of humans.
Natural wildfires are mostly caused by lightning and sometimes by volcanic eruptions. Other times, they are caused by the spontaneous combustion of dry fuels such as dead leaves and twigs, but this is rare.
Humans can start wildfires accidentally with careless campfires or sparks from machinery. Many are started intentionally like some of the wildfires in the Amazon rainforest. In the USA, approximately 90% of wildfires are caused by humans.
Like all fires, wildfires need three elements to live: oxygen, a heat source such as a lightning or a match, and fuel in the form of dry vegetation. Wildfires will travel to any place where there is an abundance of those elements and can spread rapidly with the help of wind.
There are various types of wildfires that occur on different parts of a land. Some smoulder in the ground consuming roots, duff and organic matters, while others burn on the surface, rising up to 1.3 metres tall.
The most dangerous wildfires are crown fires, which burn on treetops. These travel the fastest and can jump from crown to crown, uninterrupted by breaks in the ground that would otherwise prevent the fire from spreading.
What's more, all three types of fires can happen at the same time, increasing the amount of damage caused.
Prof Jay Mistry, a specialist in environmental geography at Royal Holloway, University of London and Associate Director of the Leverhulme Wildfires Centre, says, 'The fires we hear about in the media are catastrophic wildfires - they're the ones that have gone out of control. We hear very little about wildfires that benefit nature or fires that people are using sustainably.'
Wildfires can be a part of Earth's natural cycle, and many take place in uninhibited areas. These often burn areas far larger than human-caused wildfires do, but they go unnoticed and are not interfered with.
Wildfires can be nature's way of regenerating an ecosystem by killing insects and diseases that damage forests. They also promote new growth, keeping landscapes strong and healthy. Wildfires clear areas of old vegetation and encourage the decomposition of plants, leaving behind space and important nutrients for new plants to feed on.
A lot of natural wildfires burn at low temperatures, which means they are hot enough to burn small, dry and low-lying vegetation and some trees, but not all. Many trees in fire-prone areas, such as pine trees, have developed tough barks that protect them from low-intensity fire. The reduction in trees means natural resources such as sunlight and rain become available to the newer plants on the ground.
Some plants, such as eucalyptus, even need wildfires to help them germinate. The seeds are sealed within small, hard capsules and are released with intense heat.
Supressing wildfires in places where they normally burn causes the accumulation of dead vegetation which become a larger source of fuel for future wildfires, the kind that burn at a more intense rate than they normally would, causing more harm than good.
There are several reasons for wildfires getting worse. Since the beginning of the industrial era in 1760 Earth's temperature has increased by almost 2°C. This is having a progressively drastic impact on nature, including an increase in extreme weather such as hurricanes and typhoons.
While some areas are drowned by severe flooding, others are parched by droughts. This means many previously lush landscapes - including vegetation that can usually withstand fire - are drying out, which increases the amount of fuel for wildfires to consume.
Another reason for the increase in wildfires is that humans are expanding to wild landscapes that are beautiful but prone to fire. California is a great example. It was once a rich landscape that burned regularly, replenishing ecosystems and creating a haven for thousands of uniquely adapted species. Over time, it became a favourable habitat for humans, who have fragmented the landscape by building roads and houses.
Known as the wildland-urban interfaces (WUI), this type of land use is one of the fastest-growing in the world. The number of people in WUI at risk of fires has doubled in the last 40 years. Natural fires that previously burned regularly in those areas are now stifled to protect human habitation.
Cristina Santin, a wildfire researcher at Swansea University says, 'If you have land that needs to burn but you keep suppressing the natural fire that occurs, the fuel will accumulate.
'Climate change is making the environment drier. So if you don't let the land burn naturally, a single spark, which could be arson, accidental or lightening, can cause a huge fire - also known as a megafire - that is out of control.'
Scientists predict there will be more heatwaves and longer periods of drought as temperatures increase, making the environment more susceptible to wildfires.
Humans started controlling fire on a regular and widespread basis about 7,000 years ago, when they started using it to clear space for agriculture and possibly warfare. Over time, people started using fire in different ways depending on the part of the world they lived in.
Many Indigenous cultures embrace fire and integrate it into different aspects of their lives, from obtaining food to celebrating important ceremonies.
For example, Indigenous people in Australia burn the land to replenish the earth, encourage rain and attract small mammals for food.
In the African savanna, fires are lit to help grow nutritious grass for cattle, control the parasitic tick population and manage the growth of thorny scrubs. The savannah has evolved alongside humans and fires over thousands of years. Without regular burning, it would not exist, nor would the diverse animals it supports.
The Māori people in New Zealand believe fire is an intrinsic part of nature. Much of their culture stems from stories based around fire, which they consider to be the most important natural element.
In contrast, the West uses fire a lot less. The general European notion is that it is dangerous and should be suppressed.
The European colonisation of continents like North America, Africa, Australia and the Indian subcontinent resulted in the loss of a multitude of native cultures and identities.
Indigenous people around the world were forced to abandon their way of life and conform to European standards. A lot of important and useful Indigenous knowledge passed down for generations were lost, including how to live with fire.
Jay says, 'In some communities, people used to have a lot of traditional knowledge of how to use fire. But because of certain factors such as formal schooling or scientific organisations coming in and telling them they should do this and not that, it has changed the way people handle fires.
'A lot of what we have is a result of unsuitable policies which are all about stopping fires rather than living with it. if you try and stop it, it just gets worse.'
As our climate warms, parts of the world that are known for wildfires such as western USA and southern Australia will burn more frequently and intensely. Areas that normally burn on a smaller scale can expect to see more wildfires and on a larger scale. Wildfires are starting earlier in the season and burning longer and fiercer.
Although wildfires in the UK are much tamer compared to those in the USA and Australia, they have become worse over the past three years. There were 135 fires in 2019 and over 113 square miles of land burned in 2018 - the highest figures on record.
One of the largest wildfires in decades occurred in 2019 on Saddleworth Moore near Manchester, which burned for three weeks.
Five million people were exposed to dangerous levels of air pollution as smoke particles including carbon monoxide spread thousands of miles away.
Breathing fire smoke can cause a number of health issues such as respiratory difficulties, headaches, nausea and even premature death.
The wildfire also burned an important peatland in Marson's Moore. Peatlands are wet environments occurring in wetlands and bogs. They usually burn on the surface, which doesn't cause a lot of damage. Due to drier climate, however, some peatlands are losing their moisture and burning deeper.
Cristina says, 'Fire in peatlands are scary. Peatlands store carbon that is really old and concentrated and when they burn, the carbon is released into the atmosphere. Because peatlands grow really slowly, we won't be able to recover that carbon anytime soon.'
Soil is a non-renewable resource that is formed over tens of thousands of years through the weathering of rocks. It is made up of mineral particles, organic materials, air, water and living organisms which slowly but constantly interact with one another.
The top layer of soil, which is high in nutrients, is where most of the biological activity takes place. This includes the growth of plant roots and movement of earthworms and insects.
Wildfires impact the soil depending on the intensity of the heat.
Low-intensity wildfires can help the soil by speeding up the decay of dead vegetation, a process which would otherwise take decades.
However, high-intensity wildfires can seriously damage the top layer by killing beneficial microorganisms and nutrients such as nitrogen-fixing bacteria which is susceptible to burns, as well as nitrogen which is often vaporised and lost into the atmosphere.
Cristina explains, 'Let's consider a wildfire on a mountain. The fire has burned the vegetation and a bit of the soil on the surface. This leaves the soil fragile and sensitive.
'When it rains, the raindrops have an impact on the soil which can cause post-fire soil erosion. If this happens every hundred years, it's not a problem as nature has already adapted to cope with that. But if it's more frequent, you reach a point where you can lose all the soil.
'Without soil, we cannot have vegetation, forests, shrublands. We'll be losing one of the most important non-renewable resources in our environment.'
Wildfires can also change the property of soil. For example, intense heat can cause soil to become less porous. This is worsened by rain as water droplets clog up the pores even more. The loss of soil-promoting invertebrates such as earthworms means there is nothing there to counteract this.
What's more, water-repelling substances from litter are forced downwards into the Earth, coating the soil and mineral. This prevents further water absorption, resulting in storm run-off.
Storm run-off carries soil, ash and debris with it into nearby water bodies. It also takes valuable nutrients which causes eutrophication - when invasive species benefit from a sudden increase in nutrients, killing native species and setting a negative chain reaction on the ecosystem.
Phytoplankton and other plants experience a boom in growth. When they die, they sink to the bottom of the water, feeding the bacteria there. This increases the level of carbon dioxide in the water, which then kills the life in the water, including many which are at risk of extinction.
What's left is an oxygen-free dead zone which cannot be used in a positive manner for nature or recreation. The overall result is a saddening loss of biodiversity and ecosystems on Earth.
Many wildfires are caused by careless actions of individuals and can be prevented by being responsible. This includes never leaving a campfire unattended and making sure it has been extinguished properly before leaving.
Some fire management organisations are learning and using Indigenous practices to tackle current wildfire issues. Small, manageable fires are lit off-season to clear up dead vegetation so there is less fuel to burn during the summer. These fires are low intensity and only burn on ground level so animals and insects can take refuge on treetops.
Agroforestry is the practice of combining animals and trees in agriculture. Animals are used to graze on land to help clear up old debris and create natural breaks in woodlands. This was common practice in the past but slowly declined over the years.
Removing flammable plants such as eucalyptus and replacing them with fire-resistant trees such as oak and chestnut is also another way of slowing down and possibly extinguishing wildfires.
Researchers like Cristina are also working on projects that predict how fires move, to anticipate where they will be worst.
Cristina says, 'Houses in the UK aren't made of wood so we're fairly safe, but we need to start getting ready for more wildfires. We should consider wildfires as much of a risk as flooding.
'Luckily, we have enough time to prepare. There's been some really good collaborations between firemen and fire researchers, and the government is already including wildfire measures in the next climate change report.
'However, fire is not going anywhere, and people need to understand that. Fire is needed for some ecosystems, much like rain. If we have flooding, it's bad but it doesn't mean rain is bad. We need to appreciate fire in the same way.
'This is important because policy is driven by public perception. If people think we need a land with no fire, it's difficult for land and fire managers to convince practitioners and politicians that we need fire. So we're left with unhealthy fire suppressions that only causes worse problems down the line.
'Sometimes you just need to let the fire burn.'