The National Interagency Fire Center has data on the total number of wildfires and acres burned for each year going back to 1926. But modern data collection, with figures that can be compared year over year, began only in 1983. That year, 18,000 fires burned a little more than 1 million acres. The overall trend since that year has been a steady increase despite significant year-over-year variation.
In 1990, for instance, 4.6 million acres burned. In 2000, it was 7.4 million. The year 2015 saw a modern-day record: 10.1 million acres burned, an area larger than the state of Maryland. Last year, the most expensive fire season on record, was just as bad, and year-to-date figures suggest that 2018 will be in the same ballpark.
Total consumed acreage is increasing not necessarily because there are more fires, but because the typical fire is getting bigger. Throughout the 1980s and 1990s, the average wildfire burned anywhere from 40 to 80 acres of land. The 2010s, on the other hand, have seen several years when the average fire was more than 100 acres in size. So far this year, the average fire has burned through about 130 acres.
There are a number of factors driving these trends. Climate change is a big one. The West, in particular, is getting warmer and drier, making it easier for fires to start and spread. A 2016 Columbia University study found that average temperatures in Western forests have increased by about 2.5 degrees since 1970, which has led to the burning of about 16,000 more square miles than would have occurred had temperatures remained the same.
“Climate is really running the show in terms of what burns," study co-author Park Williams said in a statement. "We should be getting ready for bigger fire years than those familiar to previous generations.”
But that study estimated that climate change is responsible for only about half the increase in fires since the 1980s. Other factors include persistent weather patterns that have steered Pacific moisture away from the West Coast, according to the study. And paradoxically, firefighting efforts play a role: When fires are prevented from spreading, dry fuel accumulates, potentially contributing to even larger fires later.
Regardless, a warming climate means that wildfires will continue to get more severe in the decades to come.
“The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s,” according to the 2017 National Climate Assessment, “and is projected to further increase in those regions as the climate warms.”