Destructive wildfires raged across the West Coast this summer, destroying towns and chewing up millions of acres in the process. As of September 15, 5.6 million acres — an area about the size of New Jersey — burned in wildfires, according to data compiled by the National Interagency Fire Center (NIFC). Wildfires from the last 10 years burned more than twice as many acres on average as fires in the 80s.
How often do wildfires occur and how big do they get?
NIFC defines wildfires as any “unplanned and unwanted” fire that begins in an undeveloped location.
The number of wildfires nationwide varies widely each year. There were 74,126 recorded in 2011 and 58,950 recorded in 2020. The amount of land burned also varies year to year, with about 4.6 million acres burned in 2019 and over 10 million acres burned in 2020. Last year’s fires burned an area slightly larger than Massachusetts and Connecticut combined.
While the number of fires and acreage burned can vary greatly from year to year, the data from 1983 to now reveals a few key trends.
The total number of acres burned in wildfires have increased in recent decades. The average for 2011–2020 was about 7.5 million acres, slightly larger than Hawaii. That’s more than twice as much as the 10-year average of 2.7 million acres from 1983–1992.
Wildfires are burning more acres but occurring less frequently. The 10-year average wildfire frequency went from more than 80,000 a year in 2000 to less than 63,000 a year in 2020.
With fires occurring less frequently but burning up more acres, the average wildfire is more destructive. Between 1983 and 1992, the average wildfire affected 47 acres of land, the size of 35 football fields. Between 2011 and 2020, the average fire affected 119 acres, around 90 football fields.
Where do wildfires occur?
More than half of the nearly 75.3 million total acres burned in wildfires between 2011 and 2020 were in five states. Alaska and California had more than 10% of all acres burned, 15% and 14.6% respectively. Oregon (8.8%), Idaho (8%), and Texas (7%) were the other three.
In most states, wildfires destroyed less than 1% of total area in 2020. But five states approached or exceeded this threshold: California, Washington, Oregon, Arizona, and Colorado.
How do wildfires occur?
The NIFC classifies wildfires based on ignition sources, the two primary sources being lightning strikes and humans. A wildfire is human-caused if it begins via “debris burning, campfires, arson, discarded smoking products, sparks from equipment in operation, arced power lines, and other means,” according to NIFC.
Between 2011 and 2020, 87.4% of wildfires were classified as human-caused, while lightning strikes caused the rest. However, wildfires from lightning are more destructive than human sources. Over those 10 years, 54.5% of the acres burned in wildfires were caused by lightning.
Wildfires have burned 5.6 million acres so far in 2021, but it’s too early to say if this will become a record-breaking year for the US. The Dixie Fire in California is the nation’s largest current wildfire — and the second largest in California’s history — burning 960,583 acres so far.
