How the Mountain Fire was fueled by an "environmental recipe" leading to disaster

California wildfires have gotten much worse over the last two decades, researchers say. But certain conditions came together in what one expert described as an "environmental recipe" that fueled the devastating Mountain Fire in Ventura County.

And researchers say it's part of a troubling trend.

More than 10,000 people fled their homes this week as firefighters focused on saving lives when the blaze first broke out Wednesday morning. At least 10 people were injured, some from smoke inhalation while an American Red Cross spokesman said nurses at an overnight shelter treated people for scrapes and burns they suffered while trying to escape the flames.

A day after it started, California Gov. Gavin Newsom declared a state of emergency in the county.

In two days, it had destroyed dozens of homes after tearing through more than 20,000 acres, roughly the size of 32 square miles.

While firefighting efforts remain ongoing, three days later, experts have offered a glimpse into what drove the flames to spread so rapidly and the challenges that have made the blaze difficult to contain.

An "environmental recipe" for a quick-moving wildfire

The day before the Mountain Fire sparked, forecasters issued a relatively rare weather advisory known as a "Particularly Dangerous Situation" Red Flag warning, saying extremely dry, windy weather could lead to "volatile" and "extreme" fire growth. 

Once the wildfire started, powerful Santa Ana winds swept the flames and plenty of dry brush built up through an especially wet winter kept them actively burning, said Drew Smith, Los Angeles County Fire Department assistant chief and fire behavior analyst.

"We're coming off of two years of above-average rainfall, which gives us a very robust grass component," Smith said. "And those fine fuels that are receptive to warm, dry, windy (weather) support the recipe to support large fire growth when we have high winds."

"So when we have that environmental recipe, if you will, to promote this — it's because of the receptive fuel bed," he said.

How Smith described the situation as he spoke to reporters Thursday echoed what another expert said a day earlier when the fire broke out. Dr. Josh Fisher, a climate scientist at Chapman University, also said a wet winter combined with very dry brush were to blame, while saying more general implications of climate change also came into play. And it's part of a broader trend, he said.

"We're seeing a lot more wildfires for a lot of reasons," Fisher said. "The general climate change angle of things getting hotter and drier, but also, remember now, we just came off a really wet winter also related to climate change. So, this wet winter ended up growing up a lot of plants and a lot of vegetation that ended up drying out over the summer."

Why blazes in the fall and wintertime can prove worse

Meanwhile, another factor is the time of year. With the Santa Ana winds that come in the fall in Southern California, flames are driven forward and embers that spark flames can be blown into the air and carried up to three miles by the strong gusts, Smith said. And fall brings especially low humidity, including the dry seasonal winds, making the terrain ripe for extreme fire growth.

Such environmental factors, which not only intensify blazes but also make them more difficult to fight, don't exist in the summer.

"Fires during the summer are not in a wind-dominated environment," Smith said, also noting the dry conditions as a contributor.

In Southern California, the peak fire season typically runs from late spring, around May and June, until October, according to the Western Fire Chiefs Association (WFCA), which notes that climate change is leading to a longer and later fire season in the state, a known consensus among researchers. Like Smith, the WFCA says fall and wintertime wildfires can prove more difficult to put out, which the organization says often makes them more devastating than blazes in the summer.

"It is a common misconception that the most dangerous time for fires in California is during July and August," the WFCA website says. "While there may be fewer fires in September and October, the fires that do occur are far more destructive and burn through many more acres. This explosive effect is due to a combination of dry vegetation from hot summer weather, and intense dry winds that blow through the state during fall." 

The most destructive wildfires in Ventura County both occurred in the winter months. 

The Woolsey Fire broke out in November 2018 and ultimately killed three people and destroyed 1,643 structures as it burned nearly 97,000 acres. Meanwhile, the 281,893-acre Thomas Fire — which was, at the time, the largest ever recorded in California history — erupted in December 2017. It killed two people and destroyed 1,063 structures as it tore through an area of Ventura County near where the Mountain Fire is burning.

Worsening wildfires in recent years

The California Department of Forestry and Fire Protection started recording wildfires, and the destruction and death they cause, in 1932. 

More than half of the state's 20 largest fires since then have occurred in the last ten years while 15 of the 20 most destructive wildfires were in just the last 10 years, according to Cal Fire. The deadliest blaze in recorded state history was the Camp Fire in Northern California's Butte County, which broke out in the winter of 2018 and killed 85 people.

This year, the Park Fire burned through four counties in Northern California and became the state's fourth-largest ever.

It's part of a troubling trend researchers say is to blame on long-term shifts in weather caused by climate change.

"We're getting hotter, drier air that makes fires easier to start," said Glen MacDonald, a UCLA professor of geography and lead author in a research paper published last year. "It makes the fuel much drier and the fires spread faster. They're more intense, and they're more difficult to fight."

The UCLA research paper notes that less rainfall during winter, another effect of climate change, has also led to more fires.