Here's why the Bighorn Fire got so big: weather, fuel, terrain

On June 17 in Tucson, Peter Norton watched smoke billow from the Santa Catalina Mountains. His shift at Mount Lemmon’s fire department had ended the day before, but he and another firefighter, Aaron Lindflott, had made a pact. When it was time to head back up the mountain to fight the Bighorn Fire, they’d be ready.

He saw the smoke turn black above the mountain, and he knew it was time. The winds were high; fire was fast approaching Summerhaven.

“We got up there right as it was kind of coming over Samaniego Ridge,” he said. “So when the fire came over into town we were able to assist and help extinguish the fire.”

While federal firefighters commanded the fight against the Bighorn Fire, Norton helped protect houses and buildings in Summerhaven from the flames, miles away from the fire’s initial spark in the Pusch Ridge area.

As residents in Tucson watched it burn across the mountain range, some wondered if the fire really needed to get so big, or if the firefighting strategy failed at the beginning by not quickly smothering the fire while it was small.

“It’s easy to be a Monday-morning quarterback,” said Donald Falk, a fire ecologist and professor at the University of Arizona. “They were doing all they could.”

The Bighorn Fire started on June 5. It was 200 acres by the next day.

By June 17, it was nearly 23,900 acres.

And as of Saturday morning, June 27, it had grown to 95,225 acres, the biggest fire in the Santa Catalina Mountains in recent memory.

The conditions fit the “mathematical equation” for a big fire, Falk said. It’s difficult and dangerous to fight fire on steep terrain in hot, dry, windy weather among plenty of wildfire fuel.

Firefighters tried to extinguish the Bighorn Fire from the moment it started, but couldn’t.

They dropped water and fire retardant from helicopters at the beginning when the fire was smaller, but it wasn’t enough.

“The bottom line is that retardant and water don’t put fires out. Firefighters do,” said Coronado National Forest spokeswoman Heidi Schewel, adding that fire retardant and water only cool things down and slow the spread.

And many factors affect how useful these two tools are against wildfires, she said. For example, water may evaporate and fire retardant is more effective under certain conditions, she said.

On top of that, she said, private drones prevented tankers and helicopters from responding to the fire for hours on June 8.

“And that’s a big deal.” she said. “That’s time that the fire spread.”

Firefighters need to be on the ground to stop a fire, she said. But it’s not always possible to get firefighters to the fire.

The public is more concerned about the safety of firefighters than they used to be, said Stephen J. Pyne, a fire historian at Arizona State University. “People at one point would have been willing to put firefighters in 110 degree temperatures out in a desert mountain and say, ‘go at it.’ And now they’re not.”

The lightning that ignited the Bighorn Fire struck in very rough terrain.

“Much of the area covered by Bighorn is steep, rugged and inaccessible,” Schewel said. It’s not safe to put firefighters in these places. They would have had nowhere to escape or retreat from the flames.

In many of these areas, it’s hard to walk, let alone fight fire, she said, adding that helicopters cooled and slowed the fire while firefighters did their work in more accessible areas.

Firefighters dig fire lines by scraping away vegetation or any other fuel that will feed the fire. And they burn fuel themselves, with the wind at their backs, on the other side of the fire line before the main fire can engulf it. This is called “burnout.”

“Fire lines are what stop fire,” Schewel said. “Burning-out strengthens the fire lines.”

A few times near Summerhaven, fire from burnout operations crossed over the fire lines in the wrong direction, an event firefighters call “slopover,” Schewel said, adding that no buildings were burned.

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Shifts in policy

While federal firefighting policy has evolved to let some fires burn, this was never the plan for the Bighorn Fire, even though it was ignited naturally by lightning.

The U.S. Forest Service has changed its firefighting strategy during the pandemic to reduce coronavirus exposure to firefighters. In an April memo, chief forester Vicki Christiansen said the service would contain fires as rapidly as possible.

Christiansen’s memo is widely interpreted as a reinstatement of the so-called “10 a.m. policy,” Pyne said.

In 1935, the 10 a.m. policy was enacted with the goal of extinguishing every fire by the following morning at 10 a.m. But Pyne said this policy is almost impossible to reinstate for multiple reasons.

Suppressing some wildfires has become much more difficult because of factors like increased fuel loads, heightened safety measures for firefighters and climate change.

“In general, it’s not possible to stop these fires,” Pyne said. “And the more you do, the more you create conditions for worse fires.”

More wildfire fuel

An abundance of fuel has propelled the Bighorn Fire through the Santa Catalina Mountains. The forest is packed with more fuel than it used to have, leading to bigger, more severe fires.

The Bighorn Fire fed off dead wood in the scars of the Aspen, Bullock and Burro fires, Schewel said.

Buffelgrass, an invasive non-native grass, also contributed to the blaze, she said. “It provides a continuous fuel bed and carries fire where native desert vegetation is more sparse and would not carry fire as well.”

And while lower elevations have lots of fine fuels, like grass that was “cured and flammable,” higher elevations have too many trees packed into the forest, she said.

“Lightning-caused wildfires used to burn across these forests regularly, consuming fine fuels, dead and down wood and young trees, keeping forests open and parklike,” Schewel said.

Historically, wildfire suppression policies have contributed to increased fuel loads, which feed fires like the Bighorn.

“A century of fire suppression has allowed landscapes to become choked with excess vegetation, including many more trees, ” Schewel said.

This was part of the problem with the 10 a.m. policy, Pyne said. It put out all fires, good and bad.

As fuel loads increased as a result, the climate also changed.

While we can’t pinpoint climate change as a cause for the Bighorn Fire, Schewel said, “climate change is a general factor in that we now experience longer fire seasons, which can also be hotter and drier.”

The Forest Service started changing its policy in the 1970s, intending to promote good fires but prevent bad fires, Pyne said. “That’s a simple idea, in a way, but it’s very difficult to implement.”

He explained that, in general, bad fires are the ones that kill people, burn communities and destroy ecosystems, while good fires promote ecological health and help prevent bad fires.

Good and bad fires come down to judgment calls, he said. “But we’re the ones who are responsible for making those calls.”

And that’s under normal circumstances.

Coronavirus has led to old-style suppression, Pyne said.

“Two contagions meet — wildfire, COVID-19.”