What California's Wet Winter Means for Fire Season

The series of 31 atmospheric rivers that drenched California this past winter has wildfire officials and scientists breathing sighs of relief — for the most part.

According to a coalition of state and federal fire directors, which puts out regular predictions about wildfire season in Northern California (PDF), the potential for significant fires this year is normal to below normal.

That Northern California Geographic Area Coordination Center’s prediction comes from a compilation of factors, chief among them weather (past, present and future) and fuel moisture (how much water trees and plants are holding onto). Given the wet, cool winter and spring months, this year’s fire season is off to a slow start. The ground is still wet and grasses, shrubs and trees are holding onto that moisture, making them less likely to burn.

“It’s the same thing as when you try to start a campfire: You don’t use wet wood. It’s very hard to get wet wood to ignite,” said Craig Clements, director of the Wildfire Interdisciplinary Research Center at San José State University.

But what about all that extra vegetation?

Maybe you’ve heard that all that rain means more vegetation, and that more vegetation means more fuel for wildfires. That’s true — but only in certain ecosystems.

For example, you might’ve noticed grasses are extra tall this year due to all the rain. Grassland ecosystems are certainly more dense this year and once those grasses cure, they’ll be primed for burning. Thus, if conditions are ripe for fires in August, September and October, grassy environments could be at increased risk. That risk could spill over into next year, too, depending on the weather.

“This year is going to be more a function of the soil moisture content being so high,” said Clements. In other words, because grasses, shrubs and trees are holding onto their moisture longer than usual, the window for them to cure — and for severe wildfire risk — is narrower.

Plus, Clements added, grass fires are among the least concerning to firefighters.

“They’re dangerous, they spread rapidly, but aircraft suppression works really well on grass fires,” he said.

Cal Fire ramped up its flight suppression last year, which the agency said helped prevent wildfires from blazing out of control.

So where will fires be worst this year?

In short: likely in the coastal grasslands.

“If we do get significant heat waves or wind events in August, September and October, there could be a high level of fire activity in [the grasslands],” UCLA climate scientist Daniel Swain said in a recent live YouTube video.

Much of the Bay Area is considered coastal grassland and, depending on the late summer weather — particularly heat waves followed by gusty, dry offshore winds — the region could see increased fire activity later this year.

On the other hand, forest and mountain ecosystems like the Sierra Nevada are still blanketed in snow, which could mean they’ll be spared this fire season. The record-breaking snowpack in the mountains is lingering into the summer months, thereby decreasing fire danger. Even when it all melts later this summer, the fuel moisture will likely stay high enough to ward off any severe burning.

How will this summer’s weather factor in?

Of course all of these predictions are contingent upon the weather, which in California is notoriously fickle. June has already been cooler and wetter than usual, and with El Niño conditions here, that trend is likely to continue later on this year. That narrows the window for high fire danger conditions.

But that window will still exist. Although fuel moisture is higher than normal right now, the tall grasses and shrubs will cure at some point this summer, likely in August, and will be ready to burn. August, September and October are notoriously hot, dry and windy across California, and even the dozens of atmospheric rivers from the previous winter won’t be enough to quell the fire season entirely. That’s thanks in part to climate change.

“We’re getting more fire weather days and worse high fire risk days because of climate change,” said Clements. “It’s day-to-day weather that really drives fire behavior on the ground.”

One heatwave can drastically change the fire danger outlook. “It can happen just in a matter of days,” said Clements.

It’s too soon to know how those late summer months will play out weather-wise, but one thing is for sure: There will be fires in California this year. Because fire is a natural part of the state’s landscape, and many ecosystems are adapted to it and even need it to survive and thrive.