The fires currently erasing huge swaths of Northern California were fueled by a number of factors.
It’s October, traditionally the end of the state’s dry season, meaning that there’s more fuel that can burn rapidly. The fires were aided by “Diablo winds,” a phenomenon in which air from Nevada and Utah is forced from high to low elevation, causing it to grow warmer and dried and to move faster. Grist’s Eric Holthaus notes that winds in the Napa region neared hurricane force, which helped the fire spread quickly over dry ground.
In a speech Monday at the University of California at Davis, Hillary Clinton suggested another possible factor: climate change.
“It’s been a tough couple of weeks with hurricanes and earthquakes and now these terrible fires,” she said, according to KXTV in Sacramento. “So in addition to expressing our sympathy, we need to really come together to try to work to prevent and mitigate, and that starts with acknowledging climate change and the role that it plays in exacerbating such events.”
The key word there is exacerbating. Clinton wasn’t saying the fires were caused by climate change, just that climate change may have made them worse.
It’s worth noting that this year has been exceptional for the state. Using images from the National Oceanic and Atmospheric Administration, the pattern of exceptional moisture and then exceptional dryness in much of the state is clear.
The winter from 2016 into 2017 (measured from October to February) was the wettest on record. That period included a number of “extreme participation events” — periods during which an unusually large amount of rain fell. For example, the Scripps Institution of Oceanography noted that some regions west of Reno saw more than 20 inches over three days in January, powered by a “pineapple express” weather pattern. The same region saw a similar event in February.
Remember that much of the state saw severe drought in recent years. The influx of moisture helped spur a lot of new plant life. By summer, that dried out as drier conditions kicked in. By late June, during the first common fire season in California, that dry vegetation was being blamed for a spate of fires in the northern part of the state.
The summer continued, as did dry conditions. The stage was set for the recent conflagrations.
How might climate change overlap with this? It’s tempting to cherry-pick data that suggests a role for climate change that’s hard to prove. We do know, however, that some of what the state experienced this year lines up with what climate models would predict.
The Environmental Protection Agency notes specific analysis that suggests that the wildfire season in California “are expected to increase in intensity and frequency due to climate change.” A 2015 study determined that this had already begun to occur in part, Holthaus notes, because Diablo winds are expected to become more frequent and severe.
Climate models predict that extreme precipitation events will become more common, including in California. Otherwise, there may be longer periods without precipitation, which could then increase the period during which dry conditions for fires exist. (The San Diego Union-Tribune has an interview with two climate scientists about the expected changes that details why this might occur.)
Some will note that wildfires have been a constant in California for decades and that this destruction is both tragic and not unprecedented. That’s true. It’s also true that, as always, it’s very difficult to point to this particular thing and say that it is because of climate change.
But Clinton’s point was no doubt well taken by an audience who was listening to her speak about 20 miles northeast of the Atlas fire, which is currently burning over 25,000 acres, having destroyed 125 structures. Climate change is expected to make fires like that one happen more often.