The Wildfire Season Is Getting Longer—Everywhere
Call it a midsummer night’s nightmare: A few dozen wildfires are now scorching the Western and Southeastern United States.
We already know that wildfires have become more frequent, thanks to rising temperatures and dry conditions brought on by climate change. But just how much has climate change affected wildfires worldwide?
New research shows that over the last three decades, the length of wildfire season grew by nearly 19 percent—and the amount of land at risk for burning doubled between 1979 and 2013.
“Those two changes combine to explain a lot of the changes in fire activity globally over the last few decades,” said W. Matt Jolly, the U.S. Forest Service Fire Science Laboratory scientist who led the research.
Longer fire seasons put more lives and more property at risk. New research has associated smoke from increasingly intense wildfires with heart conditions among urban dwellers.
All continents—with the exception of Australia (and Antarctica, which was not part of the study)—experienced an increase in wildfire season. Some areas were affected more than others: While the season increased by a month in the subtropical grassland and savanna areas of South America, it lasted for 21 days more in Northeast Africa.
Jolly’s study was recently published in the journal Nature Communications and is the most extensive of its kind. It draws from three data sets that measured temperature, precipitation, cloud cove, humidity, and other weather conditions.
The team calculated the daily fire risk for locations around the world as measured by three fire danger indices, then came up with an average fire season length and compared it with how much this number differed from the length of a normal season.
Determining “how that played out in time and space across the globe by comparing three data sets is quite new,” Jolly said. “That’s because of two reasons—the data has become more readily available to the public, and the data now spans a period where we can look at trends over time.”
Jolly said the study identified that wildfire seasons can change in two ways: by getting progressively longer over time and by becoming more variable.
For instance, the data showed that steady increases in the length of the wildfire season took place in the Western U.S., Alaska, and the Southwest. But while the season didn’t get longer in Australia, a marked change took place more than 15 years ago.
“Since the late 1990s, what we saw is these extreme long seasons where we have these extreme fires that burn a lot of areas and heavily impact the public, and in a lot of cases they were preceded by very wet years,” Jolly said. “So swings between wet years and dry years in Australia are increasing.”
What do these results tell us about how we can better prevent, prepare for, and manage our response to wildfires?
“We have to recognize that these changes are happening and use this information to be prepared for increased wildfire activity,” Jolly said. “If we recognize that we can’t control the weather in the short term and the goal is to keep the public safe and prevent fire, then we have to reduce hazardous fuels and reduce ignition sources.”
But Jolly said his study—which focused on weather as a driver of wildfire, not on human activity or an increase in material that can ignite fires in the first place—is only the first step in understanding wildfire from a regional and global perspective.
“We need to look at satellite data to map fire activity, see where weather has a heavy influence on fire activity, and see where human activity is a major driver as well,” he said. “This will allow us to describe how these changes might impact the world more completely.”