Fire and Flood: Climate Change in California

Like many autumn nights in Sonoma County, California, October 8, 2017, was warm, dry, and windy. After months without precipitation and years of drought conditions, the parched dry grasses easily caught a spark that within hours had raged into a full-blown wildfire that jumped eight lanes of Highway 101 in Santa Rosa. Residents in neighborhoods were awoken by bullhorns and fled in their nightclothes with little to nothing else. The Tubbs Fire became the most destructive in California’s history, incinerating some 5,000 structures and costing over $1 billion in damage.

Just three months later in the very same county, thousands of people were evacuated and hundreds more homes destroyed—but this time the culprit wasn’t fire, but flooding. After days of excessive rainfall, the region’s Russian River rose three feet above flood stage, trapping cars, destroying homes, and felling trees.

According to climate scientist Daniel Swain of the UCLA Institute of the Environment and Sustainability, these two seemingly polarized events are connected, and both are caused by climate change.

“The emerging expectation is that the signature of climate change in California will increasingly be this hydro climate whiplash, which explains both ends of the spectrum,” says Swain.

According to a report by the California Climate Adaptation Strategy, the daily maximum average temperature, which has already risen by 1- or 2-degrees F, is expected to rise another 5 degrees by mid-century. These warming air temperatures leach more moisture from the soil, which, together with the extreme winds common in fall, create the perfect wildfire conditions.

“Each fall is a race between wind and rain,” says Swain, and in the past decade, winds have won. The largest wildfire season recorded in California’s modern history was in 2020, with some 10,000 fires that scorched a total of 4 million acres.

This “episodic aerification of the landscape,” can best be understood by the metaphor that Swain calls “the expanding atmospheric sponge effect.” With each degree of warming, the atmosphere increases its capacity for holding moisture by 3-4%, essentially creating a sponge that instead of, say, holding a glass’s worth of water, can now hold gallons’ worth. All that moisture is eventually unleashed, increasingly in the form of heavy concentrated atmospheric rivers.   

“The amount of total rain might not change that much,” explains Swain, “but the extreme rate of events does change. We are experiencing 5 to 15% more intense rain than without global warming.” In terms of economic loss, he warns that flooding might be just as bad as wildfires, as evidenced by the catastrophic flooding this winter, which left over a thousand people in San Diego temporarily homeless.

And, of course, all this precipitation contributes to the growth of more vegetation—and more fuel for the next wildfire.