Heavy Winter Precipitation May Not Impact Fire Season in California

Wet weather may seem like good news for the drought-plagued state, but a new study finds that it will have minimal effects on wildfire season.
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A wintry mix of precipitation falls during an unusually cold winter storm system on February 21st, 2019, in Los Angeles, California. Some parts of Los Angeles County received a brief dusting of snow during the storm.

A wintry mix of precipitation falls during an unusually cold winter storm system on February 21st, 2019, in Los Angeles, California. Some parts of Los Angeles County received a brief dusting of snow during the storm.

This winter has been abnormally wet for California, which seems like good news for a state that has been plagued with a long-lasting drought and devastating wildfires in recent years. However, a study published Monday—the day before another atmospheric river hit Southern California—in the Proceedings of the National Academy of Sciences found that heavy precipitation in the winter months will have minimal impact on the severity of wildfires later in the year.

The research team led by Eugene R. Wahl studied the behavior of the North Pacific jet stream (NPJ), which has had a historically strong influence on winter precipitation and summer fire conditions in California, from the 17th century to the present. While the relationship between the NPJ and extreme precipitation has remained strong, the researchers found the relationship between the NPJ and extreme fires has deteriorated since modern fire suppression began in the 20th century. Other factors have since overshadowed the NPJ with their influence over fire severity.

Fire suppression techniques have inadvertently contributed to the severity of future fires by increasing the build-up of organic materials that serve as fire fuels on the forest floor. Meanwhile, climate change has created hotter, drier temperatures. Researchers at the University of California–Los Angeles predict climate change will lead to increased whiplash from cool, wet weather to hot, dry weather. With most precipitation concentrated in the winter months, conditions that cause severe fires are expected to increase in the summer.

"It's not either climate change or historical fire management—it's really a combination of the two that's creating a perfect storm for catastrophic fires in California," one of the study's lead researchers, Valerie Trouet, told EurekAlert.

The new study simulated future conditions with higher carbon dioxide levels, and, during these simulations, found that hotter, drier summers would be increasingly likely despite the influence of the NPJ on precipitation levels. "Recent widespread fires in California in association with wet extremes may be early evidence of this change," the study says.

Critics question the findings of the study, noting that drier winters have historically correlated with severe fire seasons.

"On the face of it, the study makes sense, but I'm not seeing enough in the way of looking at individual storms," Jan Null, a meteorologist who has long analyzed rainfall and fire intensity in California and was not involved in the new study, told the San Francisco Chronicle.

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