This isn’t a problem when the winds arrive after the rains do. But when they arrive before the seasonal rains are able to saturate the land, as they did this year, last year and in 2017 when the Thomas Fire burned for over a month, it sets the stage for wildfires. Under these conditions plants and other ignitable material that had already spent months being dried out by hotter summer temperatures, became even more dried out by the winds.
And all that’s needed to start a fire is a spark. This time of year, that tends to be caused by people or human infrastructure, according to Dr. Williams, because lightning is rare.
In recent years, wildfires have been ignited by things as varied as a gender reveal firecracker in 2017 and a garbage truck dumping burning trash. Electrical equipment from the California Utility PG & E has sparked several wildfires, costing lives and burning hundreds of thousands of acres in recent years.
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A Changing Climate
In California, natural factors are happening atop of a changing climate. “These fires are probably bigger now than they would have been 100 years ago in the same meteorological situation,” Dr. Williams said.
“It is fair to say that everything that’s occurring today is about 3 degrees Fahrenheit warmer than it would have been if the same Santa Ana wind event were happening 100 years ago and that’s important,” he said. Hotter temperatures dry out plants, making it easier for them to catch fire, which is why there’s such a strong association with hot weather and wildfires.
In the case of Coastal California, in particular, there may be at least one more factor as well.
The state has a lot of nonnative grasses and plants — most notably the highly flammable eucalyptus plant. After a landscape burns, these nonnative plants seem to grow back faster than their native kin, making it easier for them to spread. And these nonnative plants are easier to ignite. “Nonnative vegetation species are more flammable or better at spreading fire than what would have been there otherwise,” said Dr. Williams.
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