A firefighting air tanker releases fire retardant while battling the Mosquito Fire in September in unincorporated Placer County. What is wildfire risk in the Bay Area and Northern California?
Stephen Lam/The ChronicleThe historic winter that brought record-breaking rains to parts of Northern California seems long past, as a heat wave brought above-average temperatures to large swaths of the Bay Area late last week. With theheat came firein San Bernardino County, as the Nob Fire burned 200 acres of thick brush, and firefighters had contained 5% of its perimeter as of Thursday.
- Fire Map & Tracker:Wildfires burning across the Bay Area and California
Such brush andgrass fireshave been top of mind for fire scientists and officials, but the risk for these blazes in Northern California hasn’t unfolded along the typical timeline, as recent months have brought cool, cloudy weather and evenbouts of frost。
“It’s (been) a herky-jerky start to the growing season,” said Brent Wachter, a fire meteorologist with the Northern California Geographic Area Coordination Center’s Predictive Services unit.
The prolonged stretch of cold, wet weather in recent months means that this spring and summer, the risk is generally low for significant wildfires to break out across Northern California, experts say.
“We should have a lower risk of wildfire for (the) majority of the summer,” said Craig Clements, professor of meteorology at San Jose State University and director of the Wildfire Interdisciplinary Research Center.
Vegetation will inevitably dry out as the weather trends hotter, serving as potential fuel for wildfires if conditions align. While predictions on how autumn —peak wildfire seasonin California — will play out are premature, weather patterns, including the anticipatedreturn of El Niño, could usher in conditions conducive to flames.
Slow start
Typically by April, plants in the Bay Area and Northern California have abundant new growth. But the growing season is currently running several weeks behind schedule. At this time last year, grasses at lower elevations had already sprouted and dried out, well ahead of average.
“It’s a night-and-day difference,” Wachter said.
This slow start is good news for the wildfire outlook, as plants grow into May.
Hikers take in a hillside covered in wildflowers at Fort Cronkite in Sausalito. The winter’s frequent rains spawned heavy grass growth, but the high moisture content and deep snowpack may make brushfires less likely this year.
Lea Suzuki/The Chronicle“They’re going to have higher fuel moisture content later into the season,” Clements explained.
草,今年将丰富的名单e fires that generally can be contained more easily than forest blazes, which burn through dense vegetation and trees.
“We get tons of grass fires all the time,” Clements said. “They get into the shrubs … so they can become problematic. But it’s not really a big concern.”
Over the past 40 years, above-average grass growth hasn’t correlated with an increase in significant wildfires during the Northern California fire season, Wachter said. Other variables are also at play, especially whether fires coincide with offshore winds that rapidly disperse embers and flames.
Epic snowpack
There is a stronger correlation between the Sierra snowpack and the subsequent fire season.
“Most of the above-normal snowpack years over the past 20 have led to below-normal amounts of acreage burning in Northern California,” Wachter said.
The statewide snowpack during water year 2019, for example, came in at 161% of average on April 1, according to data from theCalifornia Department of Water Resources。那一年,大约有278000英亩在燃烧state, according to data from theCalifornia Department of Forestry and Fire Protection— far below average, Wachter said.
This year’s Sierra snowpack isamong the largest on record, registering at 236% of average on April 1, when California’s snowpack typically peaks.
As a result, higher-elevation regions are likely to face low fire risk in the coming months, said Daniel Swain, a climate scientist at UCLA and the Nature Conservancy, during anonline presentationthis week.
“The first half of the fire season there might still be snow on the ground,” Swain said. “And the second half of fire season we’re still going to see residual soil moisture at higher-than-usual levels when the snow does melt.”
Especially above 7,000 or 8,000 feet, Wachter doesn’t foresee large fires for months.
“Those soils are going to be moist, and all those shrubs and tree canopies should be pulling moisture,” Wachter said.
Future weather
But the situation will inevitably change over the summer and into the fall, when dry, hot conditions set in.
“Once those grasses start to cure, (wildfires) are going to have a better chance to escape and grow a little bit further,” Wachter said.
Fortunately, there is some rain, and even potential snow, in the forecast for next week.
“We’re not done with storms yet,” said Paul Pastelok, a senior meteorologist with AccuWeather, Inc. “They’re not going to be like they were early in the spring and winter, but I do think it can have some impact in holding back the start of fire season.”
Another wildcard for the fire season is whatthe shift to El Niño conditionswill mean for California. One possibility is that things will be hotter and drier.
“Some of the forecast models … support higher pressure building (in) late summer into early fall over the Northwest and over the Western U.S.,” Pastelok said. The correlation is strongerwith intense El Niño events, though, and how conditions will evolve this summer is still uncertain.
But how the fall unfolds depends on other factors too, like water temperatures off the California coast and whether conditions promote offshore winds that fan flames. Conversely, El Niño conditions support tropical systems in the eastern Pacific, which could prematurely end the fire season, like the remnants of Hurricane Kay did in 2022.
“It’s only April,” Pastelok said. “It’s tough to exactly get what’s going to happen (in) August, September and October.”
Reach Jack Lee: jack.lee@sfchronicle.com
