'We're drying the fuels': How climate change is making wildfires worse in the West

As flames tore through California’s Santa Cruz Mountains, Craig Clements drove toward the fire in a specialized radar-equipped Ford pickup, watching the plume of smoke billowing from the forest.

Clements is a professor who leads San Jose State University’s Fire Weather Research Laboratory, and he chases wildfires to study their behavior.

As the late afternoon sun filtered through the smoke on Aug. 19, an orange glow enveloped the road and the forest. Ashes, oak leaves and twigs from burning fir and redwood trees rained down from the smoky sky.

Clements parked on a roadside about two miles from the active fire zone, and together with a graduate student, he turned on the generator and powered up the radar.

The radar allows them to measure the winds inside a fire, to see the most active parts and to track where the smoke is going and how high it’s rising into the air.

Clements and his students have had a lot to study in the explosive surge of fires in California this summer.

Wildfires sparked by an unusual siege of lightning have been raging through parched forests, brush and grasslands across Northern California. The fires have burned more than 1.3 million acres, an area bigger than the state of Delaware. At least seven people have died.

The fires have destroyed more than 1,800 homes and other buildings. More than 100,000 people were told to evacuate from their homes.

In Colorado, four large fires have burned more than 200,000 acres this year. And in Arizona, more than 800,000 acres have gone up in flames.

In the mix of factors that have influenced California’s fires, Clements pointed out that the past winter brought little rain.

He’s seen the dryness while snipping off branches from plants at three sites where he and his students take samples to monitor the fuel moisture. Beneath the green foliage in early August, he saw brush that was dying and gray.

Analyzing samples from the living plants, they found the moisture well below average for this time of year and on par with the levels in 2014-2015 during California’s severe drought. By this July, the vegetation was already as dry as it typically is in August, Clements said, “so we were a month ahead of the dryness.”

Then in early August came record-breaking heat across the Southwest. The heat further compounded the drying.

“That exacerbates the fuel moisture and causes it to decrease even more,” Clements said. “So, that sets the stage for higher intensity fires.”

When the lightning storms struck, the dry vegetation was primed to burn.

Scientific research has shown that dryness has been intensifying in the West in recent years with climate change. As global temperatures have risen, the heat has contributed to drier conditions.

Clements said he thinks of climate change functioning something like a carpet in a room, which raises the level of the furniture higher off the floor. As that baseline level is pushed higher, he said, the fuel loads in forests are becoming drier than they would be without the influence of climate change.

“We’re raising that floor a little bit more,” Clements said. “It’s well established that climate change has impacted aridity and dryness of fuels and decreased soil moisture. And so when you then think about fire behavior, the fuel moisture content, it increases the fire danger.”

When the conditions and fuels are drier, he said, that produces bigger, hotter fires.

The CZU Lightning Complex Fire, which Clements visited, has now burned more than 81,000 acres across the Santa Cruz Mountains, reaching all the way to the coast. It has become the largest wildfire in the area since flames raged through the mountains in 1904 and 1905.

Over the past few decades, people in Western states from Arizona to Colorado have lived through fires that have grown bigger, more destructive and costlier in lives and property lost.