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Record-breaking wildfires are happening with increasing regularity across the world. Between 2019 and 2020, Australia battled its worst wildfire season in recorded history and, in the summer of 2021, more than 300 wildfires spread through northeastern Siberia, burning 84,000 sq km of arctic boreal forest – an area the size of Ireland.
Devastating wildfires have raged across the west coast of North America, particularly in drought-hit California where the state’s largest-ever single fire, the 2021 Dixie Fire, destroyed 1,329 homes. According to the California Department of Forestry and Fire Protection, eight of the state’s ten biggest fires on record have happened within the past five years. Throughout the United States, the area damaged by wildfires has doubled since the 1980s.
How wildfires are started
Wildfires burn annually and have done so for hundreds of millions of years. These fires are unplanned and uncontrolled, occurring in the forests, grasslands and peatlands found on most of the world’s continents. They are especially common in regions where the climate is wet enough for vegetation to grow, but where there are also long periods of hot and dry weather, like in parts of Australia, Southeast Asia, South Africa, the Mediterranean and North America.
For a wildfire to start it needs three things: fuel (dry vegetation), oxygen and a heat source. Some fires are sparked naturally by lightning or the sun but, more commonly, they are created by human activity. In the United States, an estimated 85 to 90 per cent of wildfires are started by campfires, power lines, discarded cigarettes, arson and other man-made causes.
The map above, from the Global Forest Watch, shows all recorded fires that have happened within the last month. Different regions have different fire seasons, which are characterised by high temperatures, low humidity and often by storms and strong winds.
Not all forest fires are wildfires. Some fires are intentionally started to burn and clear space for crops, a process known as slash-and-burn agriculture, and some are prescribed burns, where planned and controlled fires are used to regulate the health of a forest or reduce the risk of a wildfire.
To some extent, wildfires are part of the annual cycle of many ecosystems. Some plants and animals have even evolved to depend on them, such as several species of North American pine that store their seeds in thick, resin-coated cones, which then open up during a fire, or the line-leaf conebush, Leucadendron linifolium, a South African evergreen shrub that requires smoke for its seeds to germinate.
Wildfires provide other ecological benefits by burning dead and decaying organic matter, which releases nutrients into the soil, making it more fertile. They thin forest canopies and undergrowth, letting more sunlight through to the forest floor which also allows seeds to germinate.
However, while the existence of some wildfires is natural and beneficial, the extent to which they are currently burning is not.
Climate change
One of the reasons behind the increased size and severity of recent wildfires is climate change. Violent wildfires occur in places affected by a combination of drought, high temperatures and thunderstorms, and climate change is making all of these conditions more common.
Between 1978 and 2013, the overall length of wildfire seasons worldwide increased by almost 19 per cent, making them 40 to 80 days longer on average. This has led to drier vegetation which increases the risk of fires starting, the speed at which they can spread over an area and the intensity at which they burn.
Forest management
Another reason behind the increased destruction caused by wildfires is that, as populations have grown, more people are now living in areas where wildfires happen, putting more homes and lives at risk.
Historically, humans have used fire to manage their environment for thousands of years, but many countries currently suppress fires in areas where they were once allowed to burn through the understory. In the United States, 98 per cent of wildfires are contained and extinguished while they are still small. However, preventing fires from burning over larger areas means an increase in the amount of dry vegetation so that, when fire escape containment, they burn more fiercely and spread higher into the canopy, killing trees,
Similarly, prescribed burning, which has long been used in Australia as a method for preventing wildfires by reducing the amount of dry, flammable vegetation and materials, is less effective due to a smaller window of time – controlled burning can only be done in cooler, damper weather with low wind speeds, to avoid the fire getting out of control.
