The nights have gotten hotter and drier in the Western US, which is making it harder to stop wildfires. Fires burn later into the night and pick back up earlier in the morning than they used to, firefighters say.

New research backs up what firefighters have seen and finds that there’s been a pretty dramatic shift in the night air in just the past few decades. The night air’s drying power, or vapor pressure deficit, has risen sharply in the past 40 years — as much as 50 percent above the previous average in the 1980s in the southern Sierra Nevada.

“I was surprised—it’s unusual to see geophysical data change that dramatically,” Andrew Chiodi, a research scientist at the University of Washington, said in a statement yesterday. Chiodi was the lead author of the new research recently published in the journal Geophysical Research Letters.

Hot, dry weather parches the landscape, creating more fuel to feed fires. In the evening in the Western US, temperatures traditionally get a little cooler and humidity rises. Vegetation soaks up some of that moisture, making it a less volatile fuel for wildfires. That would give firefighters a little bit of a breather at night or an opportunity to get ahead of the blaze while it moves at a slower pace.

“Nighttime is an important time in fire management. When fires die down at night it gives firefighters a chance to rest, move equipment and strategize,” Chiodi said. But they’re losing that advantage.

During the evening of August 4th, the Dixie Fire grew explosively overnight. The inferno destroyed much of the town of Greenville, a community that dates back all the way to California’s Gold Rush.

“We lost Greenville tonight,” local Rep. Doug LaMalfa (R-CA) said as he held back tears in a video posted to Facebook on August 5th. “There’s just no words.” The fire stayed active — and “very active” in some parts — overnight again on August 5th and was still just 35 percent contained as of August 6th morning.

LaMalfa has a history of skepticism on climate change. But evidence is piling up showing that California’s fire seasons are growing longer and more intense as the world heats up. 2020 smashed the record for the most land burned in a single season, more than doubling the previous record.

“We’re seeing truly frightening fire behavior … We have a lot of veteran firefighters who have served for twenty, thirty years and have never seen behavior like this,” said Plumas National Forest supervisor Chris Carlton during an August 5th evening update on the Dixie Fire, which he described as “extreme.” “We really are in uncharted territory around some of these extreme large fires,” Carlton said.

While there are other factors at play that researchers still don’t fully understand, climate change is also playing a role in making fires more devastating at night. Average temperatures in California have risen faster than the global average. There’s been an even steeper rise at night than during the day.

Nights are actually getting hotter across much of the world. There are apocalyptic images of a coal-fired power plant flaming in the night — on the same evening that the Dixie Fire tore through Greenville — as Turkey battles catastrophic blazes.

https://www.theverge.com/22612874/wildfires-worse-night-hot-dry-california-us-west