‘We dread summers’: dangerous ‘fire weather’ days are on the rise in northern California

By John Upton, Climate Central and Maanvi Singh, The Guardian

The Dixie fire ranked as the second-largest California wildfire on record - surpassed only by the million-acre-plus August Complex fire of 2020. Photograph: David Swanson/Reuters

This story was produced through a partnership between The Guardian and Climate Central.

On late summer and autumn days, when the hot, howling winds sting the skin and chap the lips, Holly Fisher starts to feel a bit unsettled. So do many of her neighbors in the town of Paradise, a name that evokes bitter irony in northern California.

“It feels eerie,” she said. Three years ago, this arid, blustery weather portended the Camp fire. It consumed the town, killed more than 80 people, and burned down Fisher’s home. As the region reeled in the aftermath, the same potent convergence of weather conditions – known as “fire weather” – helped fuel the North Complex fire in 2019, and the Caldor and Dixie fires this year.

Across the Sierra Nevada foothills, fire weather is increasingly becoming a distressing reality of life. Over the last half-century, global heating has dramatically increased the number of annual fire-weather days in the region, a Climate Central analysis of federal weather station data shows.

The Climate Central research reveals that the number of annual fire-weather days in what the National Oceanic & Atmospheric Administration (Noaa) defines as the Sacramento Drainage climate division climbed from an average of seven days in the early 1970s to 22 in 2020. This year there were 25.

The number of fire weather days has jumped from seven in the early 1970s to 25 in 2021.

Analysis of weather station and fire data also indicates that after the Dixie fire erupted in mid-July this year, nine of the ten days in which it grew the most explosively were characterized by fire weather conditions. The blaze tore through 1m acres of forest and razed much of the city of Greenville.

The new analysis found that a similar trend is bearing out across much of the US west. From the Pacific coast to the Great Plains, the number of fire-weather days is increasing. In some regions, fire weather has come to characterize nearly a quarter of the year.

The findings are consistent with a growing body of research suggesting that California is entering an unprecedented new era of fire. Climate scientists have found that in parts of the state, fall fire-weather days are expected to double by the end of the century. California’s fire season, which has historically peaked in the late summer and autumn, has been expanding.

“Stringing together many extreme fire-weather days in a row allows fire sizes to quickly escalate,” said John Abatzoglou, a climate and fire scientist at the University of California, Merced, who advised the Climate Central analysis and co-authored the research regarding fall fire weather.

“We used to have a lot more regional fire hotspots and now those hotspots are growing. It’s a contagion and that is certainly compromising our ability to manage fire,” said Abatzoglou, adding that the changes are creating “synchronous” fire risks across the region– and the world – making it more difficult for governments and agencies to backstop one another with firefighters and equipment.

What is a fire-weather day?

Based on the approach taken by federal storm forecasters at NOAA, Climate Central characterized a fire-weather day as one when, for two consecutive hours within the same day, the temperature reached at least 40F (5C) in winter, 50F (10C) in the summer or 45F (7.2C) during spring and autumn; when winds blew at sustained intensities of at least 15 mph; and when relative humidity neared thresholds adopted by storm forecasters in various regions. During peak fire season, relative humidity in many parts of the west dip to single digits.

Characterization of fire weather by Climate Central.

On days with fire weather, a small spark could ignite a megafire in a landscape that has been primed to burn by decades of prolonged drought.

The combination of rising temperatures and low humidity also sucks moisture out of the soil, further allowing flames to zip across forests and towns, uninhibited by moisture.

“Everything is so dry that as soon as you blow one of those embers out of the existing fire perimeter, things just catch like that,” said Karen McKinnon, a scientist at the University of California, Los Angeles, who studies climate breakdown and destructive weather.

Global heating and build-up of flammable vegetation have contributed to the increase in wildfires.

McKinnon’s research has examined the role of climate change in driving dryer conditions that are leading to the increase in the recent fire weather, but she pointed out that “it’s not just related to climate”.

In northern California, fires like the Dixie fire have been further fueled by massive build-ups of vegetation – which has accumulated on the landscape during a century of aggressive fire suppression.

“I’m always feeling like a sitting duck,” said Trina Cunningham, the executive director of the Maidu Summit Consortium, who saw a tribal health center, the homes of several members, and a 2,325-acre expanse of culturally important land burn up in the Dixie fire. “The velocity of the fire was just mind-boggling,” said Cunningham. “I couldn’t even comprehend it.”

Her two sons, who work for local fire crews, narrowly escaped the blaze as it bore down on the town of Greenville and surrounding areas where many Maidu tribal members lived. As she watched the wind pick up, her eldest reported that he was safe – but the crew’s truck and equipment were destroyed.

As drought and fire weather simultaneously overtake regions across California and the west, fire crews have been strained and short-staffed.

By then, Cunningham had begun frantically making calls, appealing to local fire chiefs and the Bureau of Indian Affairs to send more firefighters to the region. “I kept asking – we need help, we need support,” she said. Eventually, a small crew did arrive – but thousands of acres had already burned.

“It’s been really frustrating to have to sit there and watch year after year of neglect take its toll,” she said. “We need to start tending to our landscape as we tend to our gardens.”

For Cunningham, the comment is more than metaphor. For centuries before European colonization, California Indians kept forest fuel loads under control by using what foresters now call “prescribed burns”. Today many critics say the practice is underutilized. To reduce the fire risks wrought by the increase in fire weather, experts have for years been calling on western states and the federal government to radically boost the use of prescribed fire to clear would-be fuel from forests.

With extreme fire weather in the mix, firefighters can no longer expect cooler, more humid night conditions to help them tamp down big blazes. As drought and fire weather simultaneously overtake regions across California and the west, fire crews have been strained and short-staffed.

“A lot of us here had come to dread summers, because we know that there’s always a potential for a crazy fire season,” Cunningham said. In the aftermath, “there’s been so much fear, anger, trauma – and just sheer exhaustion”.

Californians have had to cope with a seemingly nonstop cycle of disasters in recent years. But the expanding season and growing intensity of wildfires creates a new level of anxiety, according to David Baron, a neuropsychiatrist at the Western University of Health Sciences in Southern California.

“In California you learn, ‘Yeah, earthquakes can come, the big one might come,’ but you almost tend to deny it to some degree,” said Baron. “Fire is a different story because every fire season they’re getting worse and worse.”

Climate Central’s analysis shows that nearly the entire state appears to have been affected by more frequent fire weather, though no data is available for a narrow band of the state’s north-eastern corner. Other states are also seeing stark changes. In parts of New Mexico, Texas, Oregon and Washington, fire weather is at least twice as prevalent as it was 50 years ago.

To combat the increase in fire weather, there’s scientific consensus that the global economy must be flipped from reliance on polluting fossil fuels to 21st-century technologies. For example, local electrical grids powered by solar and wind energy, augmented by battery storage, produce negligible carbon pollution, and they reduce threats from long-distance transmission lines, which have sparked some of California’s deadliest and most destructive fires.

“I don’t think that these big wildfires are going to stop until something really gives,” said Fisher. Paradise is unlikely to burn again in the near future – there’s not much left to burn. “But I worry for other communities, about who’s going to be next.”