Dry lightning sparks some of California's most destructive and costly wildfires

A new study has found that dry lightning outbreaks are the primary trigger for some of the largest wildfire outbreaks in modern California history. . Despite this, dry lightning has remained largely understudied in this region – until now.

Researchers from the School of environment at Washington State University in Vancouver have developed the first long-term climatology of dry lightning — lightning that occurs with less than 2.5 mm of precipitation — in central and northern California, published today by IOP Publishing in the journal Environmental Research: Local climate.

“Wildfires are a growing threat in California as the climate continues to to warm up. Unlike human-caused fires that originate from a single location, lightning can strike multiple locations and ignite many wildfires simultaneously, creating a significant challenge for fire response,” says Dmitri. Kalashnikov, doctoral student and main author of the article. “This happened recently in 2020 when several lightning-caused fires burned nearly a million hectares in this region, and other widespread wildfires caused by lightning also occurred in 2000 and 2008.”

Team used Nationwide Lightning Detection Community daily lightning counts and precipitation observations from 1987 to 2020 in combination with atmospheric reanalyses to characterize dry lightning climatology and associated weather patterns during the warm season (May-October) when wildfire risk is highest..

They found that high humidity and instability in the atmosphere – above a low, warm, dry atmosphere – were the main drivers of dry lightning in all regions of the world. central and northern California and that generalized epidemics Dry lightning events can occur any time between May and October. even in “quiet” years for lightning activity. By categorizing widespread dry lightning days, they were able to identify four distinct large-scale atmospheric patterns associated with outbreaks that exhibit different weather system configurations.

Additionally, they have found that nearly half (%) of the lightning strikes that struck the ground during this period were in dry light conditions. While dry lightning was more likely to occur at higher elevations (>2000m) with more concentrated activity in July-August, this pattern reverses from summer to fall and lower elevations are hit more frequently in September-October. During this time of year, natural fuels are drier, which is critical to wildfires, increasing the risk.

“Understanding Lightning Meteorology drought in this region can inform the prediction of possible wildfires, help better limit the future risk of wildfire ignition in California, and can help with fire suppression initiatives, automotive firefighting resources can be strategically pre-positioned in risk areas,” says Deepti Singh, co-author of the paper.

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