This week’s broiling heatwave in the US south-west is just the start of what experts warn will be a brutally hot summer, setting the stage for an active wildfire season – even in places that don’t burn often.
Thanks to a wet winter, the dangers could be delayed in many fire-prone regions across the west, including in California forests where the threats from catastrophic blazes are often high. But the extra rainfall also helped seed invasive grasses that spread across sparse arid landscapes, and rapidly dried as temperatures rose.
These parched plants are already fueling fire. Even after a cool spring, flames ripped through the yellowing hillsides east of the San Francisco Bay Area earlier this week, a worrying sign of how quickly conditions can change. And in the south-west and Great Basin region, which includes most of Nevada and areas of Utah, Idaho, Wyoming, Oregon and California, fire season is already in full swing.
Forecasting fire is complicated. But with a greater chance of extreme heat and the promise of gusty winds in the months to come, firefighting agencies and land managers across the country are already preparing for risks to sharply rise.
A wet winter was a boon – and a threat
“Repeated heatwaves can offset the benefit of having a lot of rain,” said Dr Max Moritz, a wildfire specialist with the University of California Cooperative Extension, adding that the warming weather will squeeze more moisture out of soils and plants, especially grasses, brush and other so-called “flashy fuels” that ignite easily.
Grass fires are typically easier to contain and pose less of a threat to landscapes than those that roar through forest canopies – but that doesn’t mean they can’t turn disastrous. In March, dried grasses and high winds fueled flames that spread fast and wide through the sparsely populated ranges across the Texas Panhandle and into Oklahoma, scorching more than a million acres of cattle country. California’s Corral fire burned more than 14,000 acres, destroying one home and injuring two firefighters, and, as temperatures soared in recent days, several fires ignited in Arizona, prompting evacuations.
El Niño, a climate pattern characterized by warmer surface temperatures in the Pacific Ocean that supercharged global heating this year, also played a part in the proliferation of grasses, dousing parts of the west through the winter and spring.
Now scientists are seeing a shift. La Niña, its flipside, has a high likelihood of developing over the summer. There’s significant uncertainty in how conditions will play out, but a switch to La Niña could amplify an already risky fire season. “A thorough inspection of past years with a flip from an El Niño to La Niña in less than six months reveals an overall correlation to a very warm to hot summer,” the National Interagency Fire Center said in its recent outlook.
High temperatures will play a worrying role
The acreage burned so far this year has already eclipsed the 10-year-average, according to data from the National Interagency Fire Center (NIFC), at 183% of normal for this time, and the seasons of highest risk still lie ahead. Temperatures are trending above average across the country from June through August, according to the National Weather Service, which could set the stage for a very active fire season.
Fire danger is already high across Arizona and New Mexico, according to the Southwest Coordination Center, an agency that mobilizes federal and state resources and provides forecasts for fire conditions. Roughly a third of New Mexico is in the grips of severe drought conditions, according to the US Drought Monitor.
Risks are typically higher here in the early summer before the seasonal monsoonal moisture offers relief, but models show the late-summer rains may be delayed, expanding the window when burns can ignite and spread.
“The period of peak fire season conditions very well could linger much longer than usual through the summer and early fall months,” forecasters with the NIFC wrote in an outlook released at the beginning of June.
The NIFC’s outlook also highlights the Great Basin and the Pacific north-west as areas of concern for significant fire potential. “Much of the northern Great Basin, south-east Oregon and north-west Washington is forecast to have above-normal potential July through September.”
The climate scientist Daniel Swain echoed the warnings on Friday, noting that the Great Basin is “a part of the country where there is typically less wildfire activity”. But the invasive grasses taking root on landscapes are ready to burn. “We expect this summer to be anomalously hot and, in the Great Basin, anomalously dry,” he said in a public briefing. “We are going to see a pretty rapid uptick in grass and brush fires.”
In Oregon, optimism that a snowy winter would ease the wildfire season has given way to concerns about rising temperatures. “Due to the decline in spring rain, rise in temperatures, and windy conditions, the fine fuels in the district have begun to dry significantly,” the central Oregon fire district said in a media briefing on Friday.
In California, the season is shaping up for a late start. But the state, which has had two light fire years back to back, may not get lucky a third time. “You have a lot more vegetation growth and a lot less recent fire activity to remove some of that growth,” Swain said. “When there are fires this year, they are going to have a lot more fine fuels to combust.”
Forest managers race to get ready
In California, the slower start to the season has allowed land managers more time and resources to conduct prescribed burning in overgrown forests.
“We are so close to beating the all-time record for prescribed fire,” said Adrienne Freeman, a US Forest Service spokesperson based in California, adding that more than 63,000 acres have already been burned.
But the winter storms also left a lot of debris in California forests. Downed trees and branches that have accumulated over the last two years have now had the chance to turn to tinder. Known as “jackpots of fuel”, these layers of vegetation also add complications and dangers for firefighters when blazes ignite. “A lot of places have become difficult to access,” said Freeman.
Low and slow-burning fires are extremely healthy for forests that evolved alongside the flames, and are an important tool to mitigate catastrophic blazes that leave lasting damage on landscapes and communities. But there’s a lot more work to do, and, as the climate crisis pushes fire conditions into more months of the year, the windows to do it are shortening.
Freeman emphasized that mitigation work can’t fix everything; 90% of fires are caused by humans, mostly accidentally.
“The majority of fires we have seen in the last two weeks have been escaped burn piles, or parking on dry grass,” she said. “We don’t want people to get complacent about the fact that we have had these wet winters.”
