While many Californians are praying for enough heavy rains to slow the spread of the 6,078 fires that have burned 977,932 acres in the state this summer, firefighters and climatologists acknowledge heavy winter rains are a big factor in this season’s fires burning nearly three times as much land area as in 2023.
Fires have exploded in Southern California this month after a summer of devastating fires in Northern California, including the massive Park Fire, the fourth-largest wildfire in state history. The Line Fire, which began in San Bernardino County northeast of Los Angeles, has grown to 35,000 acres in a week, threatening tens of thousands of homes and forcing thousands of residents to evacuate.
There were 5,053 people Wildfires have burned 253,755 acres by September 11, 2023. By that date this year, about 1,000 more wildfires have burned a total of 3.85 times as many acres. Most of the increase is due to what climatologists call an “abrupt change in weather.”
Over the past four years, California’s weather has changed from a drought from 2020 through 2022 to two unusually wet years in 2023 and early 2024. That moisture has promoted a surge in so-called “fine fuels” — fast-growing, easily burnable grasses, small shrubs, moss and twigs.
Firefighters call it “one-hour fuel” because in dry, sunny conditions it is dry enough to burn in just one hour.
Climate change contributed to last year’s massive wildfires, but their severity varied by region
Grassland ecosystems are more susceptible to the recent rapid changes in weather than trees.
“Forests don’t just appear and disappear, grow and die depending on whether the years are wet or dry,” says Daniel Swain, a climate scientist at the University of California, Los Angeles, “but grassland ecosystems can be quite responsive to year-to-year changes.”
In dry years, the grassland looks like a dried-up lawn, but in wet years it is lush with waist- or head-high grass. When the hot, dry weather returns, the large amounts of grass dry out quickly and become more flammable, burning rapidly in the high temperatures, with flames racing across the ground and reaching trees and buildings much faster than a forest fire.
Wet winters and atmospheric rivers over the past two years have encouraged grass growth, but then a record-breaking summer of heat turned vast swathes of grassland into fuel.
“We just added more fuel to the fire and essentially dried it out with the record-breaking heat,” Swain said.
The Park Fire, which burned 429,603 acres in California this summer, is a good example of how grasses can spark the largest and most destructive wildfires in the West. The fire started in remote grasslands and shrublands, and most of the acreage burned was in fine-fuel ecosystems. Pushed by strong winds, the flames spread into dense vegetation and forests, where a heavy biomass load can provide much more energy to the fire. While many ground fires burn slow and low on the forest floor, with enough fuel they can easily ignite flames in 100-foot-tall tree branches and spark crown fires that race through the forest canopy.
“This is the worst of both worlds: we have overgrown grass and the forest is pretty dry,” Swain said. “When you have a wet winter followed by a record-breaking hot summer and fall, that’s what you get, and that’s exactly what’s happening right now.”
A fast-spreading grass fire can also ignite wooden fence posts, decks, landscaping and siding, spreading the fire throughout an area. Many homeowners who live in areas surrounded by grass don’t realize that their property can be just as vulnerable to wildfire threats as homes in forested areas, but experts advise that just like people whose homes are in the woods, their property needs to be prepared.
The danger is the speed of the fire: Grasslands burn quickly, especially near settlements, and driven by strong winds, any fire that does start can spread quickly and use buildings as additional fuel.
In 2021, between Christmas and New Year’s Day, a rare winter wildfire caused the worst damage in Colorado’s history in just two days. The Marshall Fire destroyed 1,084 homes and seven commercial buildings.
Ralph Bloomers, director of fire-safe communities for Green Oregon, said about 80 percent of home losses from wildfires occur in prairie areas.
“Fire just exists. Fire is inevitable,” Bloomers said. “The problem isn’t the fire itself, it’s the vulnerability of the communities we’ve built in fire zones, because we’re not going to eliminate fire from fire-prone, fire-adapted lands in the West. This is a reality of nature.”
a study Co-author Blommers emphasizes improving the resilience of at-risk communities by improving structures and landscapes around them, making them less likely to burn in wildfires and reducing the chance of ignition when fires are harder to control.
“Fire just exists. Fire is inevitable. The problem isn’t the fire itself, it’s the vulnerability of the communities we’ve built in fire zones.”
Residents in forested areas have long been advised to build fire-resistant roofs, keep bark mulch, shrubs and firewood piles away from homes, and reduce the density of flammable plants near their homes. While many residents who live in homes surrounded by grass and shrubland may consider their homes less at risk, Blommers said they should make the same effort to make their properties more resistant to wildfires. Research shows that the majority of home losses nationwide are in fast-moving fires and grass and shrubland ecosystems. Because dry grasslands are more susceptible to fires, people need to be extra vigilant and take steps to prevent fires, for example by avoiding the use of spark-producing machinery in dry grasslands.
Aside from community preparation, the public must be aware that “the vast majority of vegetation fires are caused by humans and human activities. I’m talking about more than 90 percent of vegetation fires.” [Cal Fire’s] “Fires are caused by humans and our activities,” said Isaac Sanchez, deputy director of public affairs for Cal Fire.
2023 study Studies have found that property losses from wildfires are not just a function of the amount of acreage burned. 76% of property losses in the West are due to unplanned, human-caused ignitions. In contrast to the Marshall Fire, the worst fire in history, which burned 6,080 acres, the Park Fire destroyed 375 fewer buildings but burned more than 70 times the amount of acreage. By September 11, thousands of personnel had 99% of the fire under control.
With destructive all-fuel fires becoming more frequent, “we simply can’t afford to be careless firefighters early in the season and strain our firefighting efforts,” Brommers said.
More work was needed to reduce wildfire intensity and losses associated with “rapid weather changes” in the coming years, he said.
