Author: James MacCarthy Sasha Tyukavina Mikaela Weisse Nancy Harris

New data confirms: forest fires are getting worse

Source(s): World Resources Institute
Wildfire in Australia
NASA Johnson / flickr (CC BY-NC 2.0)

New data on forest fires confirms what we’ve long feared: Forest fires are becoming more widespread, burning nearly twice as much tree cover today as they did 20 years ago.

Using data from a new study by researchers at the University of Maryland, we calculated that forest fires now result in 3 million more hectares of tree cover loss per year compared to 2001 — an area roughly the size of Belgium — and accounted for more than a quarter of all tree cover loss over the past 20 years.

World map of tree cover loss from forest fires over time (2001-2021)

In fact, 2021 was one of the worst years for forest fires since the turn of the century, causing an alarming 9.3 million hectares of tree cover loss globally — over a third of all tree cover loss that occurred that year.

Why Are Forest Fires Worsening?

Climate change is likely a major driver in increasing fire activity. Extreme heat waves are already 5 times more likely today than they were 150 years ago and are expected to become even more frequent as the planet continues to warm. Warmer temperatures dry out the landscape and help create the perfect environment for larger, more frequent forest fires. This in turn leads to higher emissions from forest fires, further exacerbating climate change and contributing to more fires as part of a fire-climate feedback loop.

Explaining the forest fires-climate change feedback loop

This feedback loop, combined with the expansion of human activities like agriculture into forested areas, is driving much of the increase in fire activity we see today, including recent record-setting fires in France and other areas in Europe.

Here’s a look at some of the places most impacted by increasing forest fires, based on the latest data:

Boreal Forest Fires Threaten to Release Deep Soil Carbon

The large majority — roughly 70% — of all fire-related tree cover loss over the past two decades occurred in boreal regions. Though fire is a natural part of how boreal forests function ecologically, fire-related tree cover loss increased by a rate of about 110,000 hectares (3%) per year over the last 20 years — about half the total global increase.

Increasing fire-related tree cover loss in boreal forests is likely due to the fact that northern high-latitude regions are warming at a faster rate than the rest of the planet, contributing to longer fire seasons, greater fire frequency and severity, and larger burned areas in these regions.

For example, in 2021, Russia saw an astonishing 5.4 million hectares of fire-related tree cover loss, the most recorded in the last 20 years and a 31% increase over 2020. This record-breaking loss was due in part to prolonged heatwaves that would have been practically impossible without human-induced climate change.

This trend is worrying because boreal forests are one of the largest terrestrial carbon storehouses on the planet, with most carbon stored underground in the soil, including in permafrost. Historically, this carbon has been protected from infrequent fires that occur naturally. But changes in climate and fire activity are melting permafrost and making soil carbon more vulnerable to burning.

These shifting forest dynamics could eventually turn boreal forests from a carbon sink (an area that absorbs more carbon than it emits) into a source of carbon emissions.

Agricultural Expansion and Forest Degradation Increase Fires in Tropical Forests

In contrast to boreal forests, stand-replacing fires are not a usual part of the ecological cycle in tropical forests. Yet fires are increasing in this region as well. Over the last 20 years, fire-related tree cover loss in the tropics increased at a rate of about 36,000 hectares (around 5%) per year and accounted for roughly 15% of the total global increase in tree cover loss from fires.

How do we measure tree cover loss from fires?

Researchers at the University of Maryland used Landsat satellite imagery to map the area of tree cover lost to stand-replacing forest fires (fires that kill all or most of the living overstory) annually from 2001-2021. Stand-replacing fires cause long-term changes to forest structure and soil chemistry, and differ from lower intensity understory fires that provide ecological benefits for many forests. The new data provides a long-term view of these types of fires over the last 20 years at a higher resolution than ever before, and helps researchers distinguish the impact of tree cover loss from fires and loss from other drivers like agriculture and forestry.

Though fires are responsible for less than 10% of all tree cover loss in the tropics, more common drivers like commodity-driven deforestation and shifting agriculture make tropical forests less resilient and more susceptible to fires. Deforestation and forest degradation associated with agricultural expansion lead to higher temperatures and dried out vegetation.

In addition, it is relatively common in this region to use fires to clear land for new pasture or agricultural fields after trees have been felled and left to dry. This is not considered tree cover loss from fires in the new data because the trees have already been cut down. However, during periods of drought, these fires can accidentally escape newly cleared fields into surrounding forests. As a result, almost all fires that occur in the tropics are started by people, rather than sparked by natural ignition sources like lightning strikes. They’re exacerbated by warmer and drier conditions, which can cause fires to rage out of control.

Wildfire risk in the tropics is further fueled by El Niño events, natural climate cycles that recur every 2-7 years and cause below-average rainfall across parts of Southeast Asia and Latin America. During the 2015-2016 El Niño season, tree cover loss due to fires increased 10-fold in the tropical rainforests of Southeast Asia and Latin America.

Similar to boreal forests, increasing tree cover loss due to fires in the tropics is also resulting in higher carbon emissions. Previous studies found that in some years, forest fires accounted for more than half of carbon emissions in the Brazilian Amazon. This suggests the Amazon basin may be nearing or already at a tipping point for turning into a net carbon source.

How Do We Reduce Forest Fires?

The causes of increasing forest fires are complex and vary significantly by geography. Much has been written about how to manage wildfires and mitigate fire risk, but there is no silver bullet solution.

Climate change clearly plays an important role in driving more frequent and intense fires, especially in boreal forests. As such, there is no solution for bringing fire activity back down to historical levels without drastically reducing greenhouse gas emissions and breaking the fire-climate feedback loop. Mitigating the worst impacts of climate change is still possible, but it will require rapid and significant transformations across all systems.

In addition to climate change, human activity in and around forests makes them more susceptible to wildfires and plays a role in driving higher levels of fire-related tree cover loss in the tropics. Improving forest resilience by ending deforestation and forest degradation is key to preventing future fires, as is limiting nearby burning that can easily escape into forests, particularly during periods of drought.

While data alone cannot solve this issue, the new tree cover loss from fires data on Global Forest Watch, along with other fire monitoring data, can help us track fire activity over time to identify trends and develop targeted, long-term responses.

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