Characterized by wet winters and hot, dry summers, California has a Mediterranean climate. High levels of rain and atmospheric rivers across the state this winter have increased underbrush growth, scientists say, which could exacerbate the intensity and damage of this year’s wildfire season.

The variability of rainfall between seasons is a driving factor behind California’s wildfire season. Typically lasting from July through October (and fanned by the Santa Ana winds) California wildfires have made headlines in recent years for their size and intensity.

According to Chris Field, Ph.D. ’81, director of the Woods Institute and Interdisciplinary Environmental Studies at Stanford University, “We’ve seen bigger fires in the last few years than ever before in California in recorded history.”

In 2020, during the largest wildfire season recorded in the state’s history, more than 4.3 million acres of land were burned.

Not only are fires larger, they move faster, Field said, which means more land area is impacted. “Sometimes the fires have been moving 50 miles an hour,” Field said. “Really terrifying to beat.”

Field explained how a dry season leads to a wildfire season. “Even if it’s not terribly hot, that long dry season really creates conditions where the fuel moisture just dropped so low that fine fuels are almost explosive.” According to Field, the best indicator for how severe a wildfire season will be is how dry the air is.

Kevin Anchukaitis, professor of Earth Systems Geography at the University of Arizona, explained that there are three main factors that contribute to a wildfire season: ignition, fuel and climate.

“In many cases these days, the ignitions are related to human activity,” said Anchukaitis. Downed power lines, poorly extinguished campfires and gender reveal parties gone astray are just some of the ways that human activity has caused wildfires. Fires started by humans generally spread at a rate of roughly 1.83 kilometers per day, which is more than twice as fast as the rate of spread for burns sparked by lightning.

Field touched on the impact of European settlers on the natural wildfire season and, in particular, on the fire return interval–a measure of the time between fires in a particular area. “Pre-Europeans, the fire [return] interval in forested parts of California, especially in the lower elevation areas, was frequent, low intensity fires. Maybe once a decade or so.”

According to Field, hotter summers from climate change lead to bigger fires. Additionally, Field said that decades of fire suppression have left California with an excess of fuel waiting to be burned. In contrast to indigenous practices of using fire to manage forests, full suppression of fires in forested areas was standard policy in California for over a century.

“We are seeing longer dry seasons and some very, very hot temperatures. That definitely creates conditions where it’s easier for a fire to go from a small fire to an explosive fire. And we also have in California and around the West, a legacy of fuel accumulation.”

Fuels help fires travel from the forest floor to the tops of trees. “The bush that’s against a small tree that’s leaning against the big trees [means] that if a fire starts down low in the forest, it’s carried by these ladder fuels up into the crown,” Field said.

According to Anchukaitis, wet winters spur more vegetation growth and “that can provide more of the kind of fuels that would allow a fire to burn if you’ve got an ignition.” He added that increased vegetation growth would exacerbate the buildup of fuel that already exists in California’s forests.

California has had a winter marked by high levels of precipitation. According to The Daily’s coverage in April, in the first three months of 2023, the San Francisco area received 19.31 inches of precipitation, rainwater and snowfall. The sum of all the precipitation the year prior was 13.42 inches, while, in 2020, the area got 5.86 inches. This year also brought record-breaking snowpack in some parts of the state.

“The quicker snowmelt disappears, runs off, fills rivers and stuff like that–that increases the chances of dry conditions that might lead to wildfire,” said Anchukaitis.

According to Anchukaitis, temperatures in California are “climbing,” so there’s “good reason to expect that [the snowpack is] gonna be a pretty fast melt this year.” Anchukaitis warned that this melting will lead to flooding, an outcome he described as “immediately worrying.”

Douglas Johnson, Information Officer for California State Parks, commented on the role of the State Parks Wildfire and Forest Resilience Program in addressing wildfires in California State Parks. “The primary focus of this work includes fuel reduction through ecological thinning, watershed restoration, and prescribed fire,” Johnson said. “The program also supports on-going recovery from wildfires when they happen.”

Regarding flooding concerns, Johnson said that “this season’s statewide snowpack [is] at 237% of average as of April 3.” He added that California State Parks are enacting temporary park closures and undergoing waterway restoration projects in order to address flood risks.

According to a joint April press release from the California Department of Parks and Recreation, Department of Water Resources and CAL FIRE in April, winter storms have caused “rising river and stream flow levels not seen in years.” Rising temperatures in the spring “will bring fast flows and cold temperatures” as snow melts.

“All Californians are being encouraged to wait until summer to recreate in the water, when conditions are safer,” the statement reads.

Johnson said that California State Parks do not protect ecosystems from floods unless human human health and safety is at stake because, “floods are natural processes, and ecosystems depend on natural processes.”

Field said the main ways to lessen the severity of wildfires involve eliminating the fuels that fires need to burn.

“Prescribed burns can be an extremely important part of our overall fire management strategy,” Field said.“The second thing you can do is often called mechanical fuel reduction, and that involves either having people with chainsaws or tractors (or sometimes goats or sheep) go in and cut up these fine fuels.”

According to Field, the problem with these methods of fire prevention is that the scale of the problem is too large. “We know in a lot of detail how to fix one square meter,” said Field. “Mechanical fuel reduction is still at the scale of well less than a million acres a year.” California, for context, has 423,969,580,000 square meters of land area.

Wildfires are not a distant issue, Field added. Stanford takes fire risk reduction measures on its own campus. “If you look around the Stanford campus, you’ll see that they’re already beginning to mow high risk fire areas even now while the grass is still green,” he said.

When asked to predict the severity of this year’s fire season, Field said, “The most likely outcome for this year is a smaller than normal area burned [for] forest fires and potentially larger than normal area burned [in] grassland and shrubland fires.”