Acreage burned by wildfires is decreasing
Expansion of agriculture may be leading to drop in land area blackened
Around the world, the total acreage burned in wildfires is decreasing — and human activity is largely the cause, scientists say. According to a new study, out Thursday in the journal Science, global burned area decreased by nearly a quarter in the past two decades. And the surprising decrease occurred largely as agriculture has expanded and intensified throughout the world, taking over many of the natural areas where wildfires commonly occur.
While many recent studies have suggested that climate change will cause longer and more intense fire seasons in certain parts of the world — recent research has suggested that it’s been making wildfires in the western U.S. more intense for decades — the new study indicates that human land-use changes also have a significant impact on when and where fires occur. Indeed, in many places, the inf luence of human land use is “just stronger than the climate signal,” said the new study’s lead author, Niels Andela, a research scientist at NASA’s Goddard Space Flight Center.
“This work highlights how humans can shape global fire regimes,” said David Bowman, a global wildfire expert and professor of environmental change biology at the University of Tasmania, who was not involved with the research, in an emailed comment. “Realistically factoring in humans into global climate change and global carbon dynamic projections has always been difficult, and this work demonstrates that this difficulty must be more thoroughly addressed to create plausible scenarios of earth system change.”
The researchers came to their conclusions by analyzing satellite data on burned area across the planet between 1998 and 2015. During this period, they found that burned area declined by about 24 percent — an “enormous area,” according to Andela — with much of the decrease occurring in the world’s grasslands and savannas.
The researchers also used a model to investigate the effect of factors like precipitation and human activities on global fire patterns. They found that precipitation had little influence on long-term decline in global burned area — but human activity, particularly agriculture, was a strong driver.
In some places, particularly tropical forest landscapes, the researchers found that agricultural activity was actually associated with an increase in fires, probably as a result of agricultural waste burning or deforestation to make room for cropland. But these increases were outweighed by the areas where agriculture was associated with a reduction in burned area, mainly in grassland and savanna landscapes, where there’s less biomass available to burn and where fire may be less necessary as a land-clearing or management tool.
Researchers found that fire reductions were particularly pronounced in places with greater socioeconomic development, and higher investment in pastures and croplands. Wealthier areas may be less inclined to risk crops, livestock, homes and infrastructure by using fire as a management tool, the researchers suggest, and the people living in these places also may be less likely to accept the poor air quality caused by smoke from wildfires. In fact, they may begin to employ fire suppression tactics to prevent natural wildfires from occurring.
Global fire reductions may come with both pros and cons, the researchers note. For one, fire is a natural element of many ecosystems’ life cycles, helping to recycle nutrients, regulate competition between plants and make space for new growth. So suppressing wildfires can have a negative impact on a landscape’s vegetation and biodiversity.
On the other hand, the researchers note that a reduction in fire also comes with a decline in the carbon emissions it produces, which could help the fight against climate change. That said, the carbon released by the land conversion and agricultural expansion driving these declines may offset the reduction in fire emissions. More research will be necessary before scientists can say for sure how all of these changes are affecting the global carbon cycle, Andela said. “The disappearance of fire from those ecosystems really symbolizes how we are using these last wildernesses of the earth,” he said.