In California, that doesn’t bode well, given that last year’s more moderate rainfall deficits, combined with extreme heat waves, ushered in a record-setting fire year. It brought 5 of the 6 largest fires in modern state history, 10,488 destroyed structures and 33 fatalities. Some 4.2 million acres were torched.
More frequent drought, hotter summers and warmer and drier autumns, tied to climate change, are stacking the deck for large and destructive fires during the heart of the fire season. And this year, a lack of rain in spring could mean fires arrive early in some areas.
In California, ominous signs of the season ahead
After a devastating 2020 fire season and a dry autumn, this winter offered a chance to reverse course on mounting rainfall deficits. But despite a significant late-January storm, the 2021 winter and spring months have failed to deliver even normal precipitation, and much of April is forecast to be very dry. In fact, the current water year is now tied for the third driest on record.
“As California got further into the wet season, it became clear that the number of major storms, such as atmospheric rivers, needed to ameliorate the drought were not coming, and drought conditions and impacts across sectors intensified and expanded,” Amanda Sheffield, an expert with the National Integrated Drought Information System, said in an email.
For the last two wet seasons, a persistent ridge of high pressure in the central and eastern Pacific has diverted most storms out of the state. In Northern California, many of the wettest, forested regions have missed over 20 inches of precipitation in that time period.
“The two-year precipitation deficits in the mountains are really going to cause plants to struggle, and I think that’s what we’re seeing,” said Craig Clements, a professor and director of the Wildfire Interdisciplinary Research Center at San Jose State University.
Last week in the Santa Cruz mountains, Clements sampled plants in a field of chaparral — flammable shrubs found throughout the state. They showed record low moisture values for April and no new growth where they should be blooming and thriving.
While he hopes that growth might simply be delayed and recover with additional spring rain, “I think we are going to see dying plants and a lot of dead fuel accumulating in chaparral across the state,” he said.
A similar situation could develop in higher elevation forests in the Sierra and Cascades.
Statewide mountain snowpack, currently at less than 50 percent of normal, is expected to melt off early, leaving Sierra forests prone to burn earlier and hotter.
Even with the very dry spring so far, grasses are still green in many areas, preventing fires from spreading quickly. But once those dry out, or “cure,” the state could be in a full-blown fire season.
“How early the fire season starts will depend on how this year’s green-up goes, and how quickly the vegetation dries due to the very low soil moisture and weather conditions,” Sheffield said.
Rain, fog and cooler temperatures would slow this drying process, while heat and wind would accelerate it.
Clements said it’s possible that grasses could fully cure in May in Northern California, which current forecasts suggest could be a particularly warm and dry month. In Southern California, grasses could carry fire by late April, about on schedule, according to Matt Shameson, a fire meteorologist with the U.S. Forest Service in Riverside, Calif.
While wind events aren’t common in late spring, some are possible in May, including warm “Sundowner” land-to-sea winds that can affect coastal Santa Barbara County this time of year and have driven dangerous fires near urbanized areas.
Drought deepens across the West, and fire risk follows
Large wildfires in the West are driven by a complex relationship between shorter-term weather and longer-term climate variability. The West’s descent into the current severe and widespread drought began in the fall of 2019, when a dry pattern emerged over Oregon, northern California, central Nevada and into parts of Idaho, Utah and Colorado. The hot and dry summer of 2020 quickly followed, which brought devastating fires to California and the Pacific Northwest, and set the stage for Colorado’s biggest wildfire season on record beginning in August and continuing through October.
This concerning situation continues: Not only is drought persisting over the same areas, it’s expanding to areas that weren’t as dry in the winter. Extremely warm and dry conditions from October to March extended across California and Oregon, and eastward across Idaho, Nevada, Utah, Arizona, and entering Wyoming, Colorado, and New Mexico.
Combining this longer-term climate signal with expected weather as we move into summer dictates the location of greatest fire risk. Based on low snowpack and early snowmelt already occurring in Arizona and New Mexico, and expected early snowmelt around the Four Corners, the risk for significant wildfires is high in Arizona and New Mexico, and is extending into southern Utah and southern Colorado. That risk moves northward as the summer continues into central Nevada, Utah and western Colorado, but should be reduced to the south if monsoon rains arrive as expected.
As the West Coast enters the summer dry season, the chance for significant fires is high. The probability of getting enough precipitation to mitigate wildfire risk has gone to almost zero as we leave the wet season behind with significant dry anomalies and low snowpack.
Early snowmelt leads to a longer dry season and an increased risk for large wildfires in high elevation forests; shifts in snowmelt timing because of climate change have been linked to a marked increase in burned area in western forests since the mid-1980s.
“When we have a dry winter and a fairly dry spring, all elevations become open for business much sooner,” Brent Wachter, a fire meteorologist with the U.S. Forest Service in Redding, Calif., said in an email. And deepening drought and low soil moisture mean that flammable elements — from ground cover to the tree tops — can be available to burn at the same time. “Thus, more potential for an ignition in the ‘wrong’ area and ‘wrong time’ resulting in rapid fire spread and increased intensity,” he wrote.
Diana Leonard is a science writer covering natural hazards in California.
Becky Bolinger is the assistant state climatologist for Colorado and a research scientist at Colorado State University.