Forest fires diminished in intensity at night. A study says this is no longer the case


By Jennifer Gray, CNN Meteorologist

The West is spiraling out of control. Warmer temperatures and historically dry conditions lead to longer durations and wildfire seasons more devastating than ever before.

And now a new study suggests that fires get bigger and stronger at night, when firefighters could gain ground.

“I have personally seen extreme fire behavior at night on the Thomas Fire in Ventura and the Flash Fire near St. Helena and Calistoga,” said Chief Jesse Alexander of the Yuba City, Calif., Fire Department. .

He fought some of the largest fires in the state and witnessed the intensity of nighttime fires. “The night changes everything,” explained Alexander. “Your senses are heightened due to the lack of visibility, which makes it difficult to accurately determine the size of the fire,” adding, “Fires always seem bigger at night.”

In reality, nighttime fires are indeed getting bigger and more intense, making them harder to fight.

New study finds nighttime fires are becoming more common

“Night fires have become more intense and frequent in recent decades, as hot, dry nights are more common,” the study by the Cooperative Institute for Research in Environmental Sciences (CIRES) found. Earth Lab at the University of Colorado at Boulder,

While scientists have found this to be true around the world, the western United States appears to be off the charts.

“Some places are definitely seeing a much bigger increase than the global situation, and the western United States is one of them,” Jennifer Balch, lead author of the study, told CNN.

The scientists used satellite images and hourly climate data from 81,000 fires around the world to measure the vapor pressure deficit, or VPD.

Weather satellites have the ability to detect different wavelengths, and one of them is the temperature of fire, as seen in a tweet from 2020.

“This is a very important variable for fire science,” Balch said. “It’s basically the combination of temperature and humidity, and it indicates how quickly the atmosphere sucks moisture out of fuels.”

“When the VPD is relatively low, the air is cool and humid and fires cannot grow,” the study says, that is, when firefighters take advantage of better conditions to help contain the fire.

However, when the VPD is high, “the air is hot and dry, parched and ready to burn,” according to the study.

Scientists have found that nighttime conditions are becoming much more conducive to the spread of fires, reporting “a full week of additional flammable nights per year in flammable lands around the world over the past 40 years.” And in the western United States, it has increased again: 11 nights, a 45% increase over the four decades (1979-2020). »

The study also used remote sensing and modeling techniques to track overnight fire progress from tens of thousands of blazes around the world.

They determined that “Globally, nighttime fires became 7.2% more intense between 2003 and 2020.”

However, in the western United States, the number was four times higher at 28% more intense.

“It’s tied to the combination of rising temperature in the West and dry or drought conditions,” Balch pointed out.

“These two factors play a large role in the heat and dryness of our nights in the western United States.”

There has also been a 36% increase in nighttime flammable hours between 1979 and 2020, while daytime flammable hours have increased by 27%.

“The fact that the fires are shifting from day to night means that we are seeing more extreme fires in terms of travel speed, operating time and magnitude,” Balch added.

Night fires burn the West

In fact, we’ve seen several nightly fires over the past few years, raging out of control and destroying entire cities.

the The Dixie Fire raged through the town of Greenville, California leveling the city in just two hours overnight in early August 2021.

In August 2021, the Caldor fire in California doubled in size, burning about 25,000 acres in a single night.

the Marshall fire near Boulder which destroyed hundreds of homes on New Year’s Eve, sprouted over 6,000 acres overnight.

And the Camp Fire, which destroyed the town of Paradise, California, in 2018was at one time burning an area the size of a football field every second overnight.

“With climate change, we’ve seen an increase of more than two degrees Fahrenheit in the West,” Balch confirmed. “What that means is that the fire is very reactive, and it only takes a little warming up to get a lot more burn.”

As nighttime fires grow more intense, so does the work of frontline firefighters.

What it’s like to fight fires against the midnight sky

“Usually the night brings a bit of respite from the physical and emotional stresses of the day, but when it stays dry, warm and windy overnight, the stakes are high and it’s anything but relaxing,” Matthew said. Jeglum, NOAA Western Region Incident Meteorologist. .

He has seen night fires from the front lines as a firefighter and meteorologist.

“Warmer, drier nights may limit the amount of time firefighters are able to do burnouts to help control the fire, which are an essential tool in a firefighter’s toolbox,” Jeglum noted.

He explained that when fire activity is high overnight due to dry conditions, it can also prevent firefighters from getting close enough to the fire to build a line of fire along the edge of the fire.

“Rather, they build lines that leave unburned fuel between the line and the fire,” says Jeglum.

Fires active at night also require more personnel to fight the blaze, requiring more work in more grueling conditions.

“Injuries increase due to lack of visibility, it is more difficult to identify and isolate dangerous trees (trees that fall on you) and fatigue can start to become a factor depending on your physical actions that have been made in the previous 16 to 20 hours,” Alexander explained.

Both Jeglum and Alexander said firefighters often have fewer resources available at night to help fight fires, especially planes.

“You won’t have planes to support you because in almost all cases they can’t fly,” Jeglum explained. “You can’t see what the smoke column is doing. Situational awareness and communication can be more difficult. It is a unique experience.

It’s a unique experience that may not feel unique at all in years to come.

Climate change is fueling wildfires

Forty years ago, temperatures cooled further at night and humidity levels increased, relieving firefighters, and “burning nights” were rare, according to the study.

Now the nights are warming up faster than the days, amid our changing climate.

“Traditionally, nighttime was when we could progress building containment lines and doing burning operations to get in front of the fire,” Alexander recalls. “On the Glass Fire (2021), we were just trying to catch it at night because it was going so fast.”

2020 was a banner year in California for the hectares burned.

Eight of the 10 largest wildfires in California history have occurred over the past five years.

In Colorado, all of the state’s top 20 wildfires have occurred in the past 20 years (since 2001).

Four of the five largest wildfires have occurred in the past three years (2018-2020).

“The fact that firefighters don’t have a break at night means they’re fighting fires 24/7,” Balch said.

This is a grim reality in a new environment of more intense and frequent nighttime wildfires.

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