Crews have struggled, at least in part, because they have never seen fires behave like this before.
“What we’re seeing in California right now is more destructive, larger fires burning at rates that we have historically never seen,” Jonathan Cox, a Cal Fire spokesman, told CNN on Monday morning. “And our message is simply, if you feel like you could be in danger, to leave the area when these fires are burning.”
The most destructive wildfire in California, the Carr Fire, went from a manageable blaze to a “war zone” overnight. On Wednesday morning, the Carr Fire was 4,500 acres and 24 percent contained, according to Cal Fire. By Thursday morning, it had exploded to 20,000 acres and 10 percent contained.
Several specific conditions are feeding the inferno. Afternoon temperatures have peaked in the triple digits around Redding, Calif., since early last week. On Wednesday, the high was 107 degrees. At the same time, winds that were persistent but manageable earlier in the day picked up, gusting to 21 mph. The dew point — a measure of how much moisture is in the air — dropped precipitously through Thursday afternoon until humidity was 10 percent as the temperature reached 110 degrees.
On top of that, the soil in Northern California is exceptionally dry. A hotter-than-average summer and a very dry winter have led to tinder-dry vegetation. When it ends Tuesday, this month will become Redding’s hottest July on record, with an average temperature of 86.7 degrees. The energy release component, or how much fuel is available for the fire, is at the highest it has been around Redding since at least 1979.
The Northern Hemisphere is warming faster than the planet as a whole, according to the World Meteorological Organization. “That heat is drying out forests and making them more susceptible to burn. A recent study found Earth’s boreal forests are now burning at a rate unseen in at least 10,000 years.”
As Earth’s average temperature warms because of human-made climate change, topsoil will continue to dry out, according to the 2017 National Climate Assessment.
“The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s,” the assessment concluded with high confidence, “and is projected to further increase in those regions as the climate warms.”
What remains a critical question is how climate change affects the winds that cause wildfires to spread.
The scene as wildfires rage across Northern California
Because of the Carr Fire’s proximity to homes, officials started ordering evacuations almost immediately. By Tuesday morning, three communities had been told to leave their homes and make camp in schools turned shelters. Since Thursday, dry winds have fanned the flames of the Carr Fire, spreading it across 100,000 acres. Thousands of people have evacuated. More than 700 homes have been destroyed, and the fire still threatens 5,000 structures, officials said.
If you ask the crews on the ground, they will tell you it’s not just the hot and dry weather that’s making fires worse. Firefighters have noted recently that fires are behaving differently than they did in the past. For decades, officials depended on a tried-and-true process to prevent wildfires from spreading: fight them from downhill. Fires naturally expand uphill because heat rises, creating uphill winds, and because the lapping flames extend upward, making uphill grass the easiest target.
But KQED reports that firefighters say that process isn’t working as well anymore — the Carr Fire being an example — and no one has a clear explanation as to why. It could be drought conditions, increased fuel load or warmer overnight temperatures that spur evening winds.
“Is that a statistically significant trend?” asked Nick Nauslar, a fire weather forecaster at the National Weather Service in Oklahoma, in an interview with KQED. “And if so, what might be causing that? There would have to be a couple more steps before I try to make assumptions or formulate theories on why that might be happening.”
It is not resolved how climate change might shift or strengthen winds that blow wildfires downhill into mountain communities. But after wildfires in Greece killed more than 80 people, the World Meteorological Organization highlighted micro-scale winds as a key wildfire forecasting problem.
In Northern California, officials are making progress on the Carr Fire, which was 20 percent contained as of Monday morning. The temperature will continue to hit or surpass 100 degrees through the end of the week in Redding, with no rain in sight.