weather explainer

When Old Fires Find New Life: The Science Behind ‘Zombie Fires'

NBCUniversal Media, LLC

Not only is the 2021 fire season off to a much faster start than last year, some lingering side effects of the 2021 Lightning Complex fires sometimes referred to as "zombie fires" appear to be coming back to life.

As Kate Wilkin, Ph.D. assistant professor of fire ecology with San Jose State's Wildfire Research Center points out, the lack of rainfall over the winter months is likely contributing to the smaller fire restarts being seen in the CZU Lightning Complex zone since the start of the year.

Seeing fires restart in an old burn scar sometimes gives ground fires the name "zombie fire" for apparently coming back to life, when in truth they've never really been extinguished at all.

Wilkin explains these smaller fires can exist near root systems or below ground for weeks or months, especially so in a well below average Winter rain season. As soon as the weather warms and wind increases, it can create a favorable environment for these smaller fires to pop up again.

Ground fires don't usually become larger events as most of the denser fuels have been previously burned by the original fire, but under the right set of circumstances like the recent Basin Fire earlier this month in the CZU Lightning Complex zone ground fires can grow to a few acres in size requiring fire crews to contain them again.

Such activity could be more common this year than previous years, given the large areas burned within denser forests and terrain around the Bay Area mountains from the year before followed by the third driest two year stretch of Winter rain seasons the Bay Area has seen in the last 150 years.

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