Did you know that wildfires are mostly a daytime thing? They are. Fires often surge most in the later afternoon, and tend to somewhat die down at night (strong winds notwithstanding), which allows firefighters to rest, regroup, or do containment overnight.
This year’s wildfires are not doing that. The West Coast fires start earlier in the morning and calm down later at night, and a new research paper from the U.S. Forest Service and the University of Washington explains why: Nighttime air has increasingly more drying power.
“Firefighters had been saying for several years that they feel some fires burn later into the evening than they used to,” said coauthor Brian Potter, a research meteorologist at the U.S. Forest Service’s Pacific Wildland Fire Sciences Laboratory, in a statement. “We found that in some areas, the amount of water in the air is decreasing, sort of doubling up on the warmer nights. These areas, including where the Snake River Complex and Lick Creek fires are burning right now, are much more likely to have fires burn late into the night.”
Night air is indeed warmer, likely due to climate change, which was thought to be fueling the new fire schedule, but the researchers found that the air has 50% more drying power, on average, than it did in the 1980s and 1990s. “I was surprised—it’s unusual to see geophysical data change that dramatically,” added lead author Andy Chiodi, a research scientist at the Cooperative Institute for Climate, Ocean, and Ecosystem Studies at the University of Washington. He says that the steep change in drying power is quite unlikely to be caused by climate change, and instead may be a part of a long-term inland weather cycle known as the Pacific Decadal Oscillation, which is arriving with unfortunate timing.
The pattern will surely continue tonight.