‘Dry lightning’ sparks the most destructive, expensive wildfires in California: study
Dry lightning bursts are the leading cause of some of the biggest wildfire flare-ups in California’s history, a new study has found.
So-called dry lightning — or lightning that occurs with less than 2.5 millimeters of rain — outbreaks are relatively rare, according to the study, published on Monday in Environmental Research: Climate.
But such sparks can cause destructive wildfires “due to the intersection of dense, dry vegetation and a large population living adjacent to fire-prone lands,” the authors found.
These findings come just days after lightning triggered eight active wildfires in Northern California, according to the U.S. Forest Service. The Six Rivers Lightning Complex, which began on Friday, is “burning in steep rugged terrain” and prompted evacuation orders this weekend throughout the surrounding Humboldt County.
“Wildfires are a growing threat in California as the climate continues to warm,” lead author Dmitri Kalashnikov, a doctoral student at Washington State University’s School of the Environment, said in a statement.
“Unlike human-caused fires that originate in a single location, lightning outbreaks can strike multiple locations and start numerous simultaneous wildfires, creating a substantial challenge for fire response,” he added.
Moisture and instability high in the atmosphere — above a hot, dry lower atmosphere — are the key drivers of so-called dry lightning outbreaks across Central and Northern California, the researchers determined.
Kalashnikov and his colleagues looked at daily lightning counts from the National Lightning Detection Network coupled with precipitation records from 1987-2020. They combined these figures with atmospheric analyses to identify the weather patterns associated with dry lightning during the May-October season, when wildfire risk is greatest.
The researchers found that 46 percent of lightning that struck the ground during this period could be considered dry lightning, with activity more concentrated at higher elevations and during the July-August window.
Lower elevations are struck more frequently in September and October, when natural fuels are drier and increase the risk of wildfires, according to the study.
“Understanding the meteorology of dry lightning across this region can inform forecasting of possible wildfire ignitions,” co-author Deepti Singh, an assistant professor at Washington State University’s School of the Environment, said in a statement.
Such knowledge, according to Singh, can help “better constrain future risk of wildfire ignition in California and can aid fire suppression efforts.”
“Firefighting resources can be strategically pre-positioned in at-risk areas,” she added.
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