U.S. Forest Service Planned Burn Caused Largest New Mexico Wildfire

A wildfire in northern New Mexico that destroyed at least 330 homes and displaced thousands of people was caused by a planned burn by the U.S. Forest Service, federal fire investigators said on Friday.

The Calf Canyon fire escaped containment lines and merged with the Hermits Peak fire, which was also caused by an out-of-control planned burn, to form the largest wildfire in New Mexico’s history.

The combined Calf Canyon/Hermits Peak fire has burned more than 312,000 acres, threatening remote mountain villages and forcing thousands to evacuate, sometimes repeatedly, over the past two months.

The fire was 47 percent contained as of Friday morning, the National Wildfire Coordinating Group said. It warned that the Memorial Day holiday weekend could pose more challenges for firefighters because of increased traffic and recreational activities that could cause fires in the dry, hot weather. Fire officials cautioned about the use of, among other things, campfires and wood stoves.

Planned burns, or prescribed fires, are important wildfire management tools that burn vegetation to limit the potential fuel for such blazes. It is rare for them to grow out of control, officials said.

Forest Service investigators said the Calf Canyon fire emerged from a “pile burn” that had been dormant from January until April, when smoke was reported from the area of the burn, which had concluded on Jan. 29.

Crews monitored the 1.5-acre fire to make sure there were no signs of flames or heat at its edges, investigators said. On April 19 — 10 days after the smoke was reported — the fire reignited and escaped its containment lines.

On April 22, strong winds caused the fire to spread and merge with the Hermits Peak fire, which the Forest Service said in April had also been caused by an escaped prescribed burn. The Forest Service did not specify how it lost control of both fires.

Debbie Cress, supervisor of the Santa Fe National Forest, said in a statement that the agency was “100 percent focused on suppressing these fires.”

“Our commitment is to manage the public lands entrusted to us by improving the forest’s resilience to the many stressors they are facing, including larger, hotter wildfires, historic levels of drought, rising temperatures, and insects and disease,” Ms. Cress said.

In response to the fire investigators’ findings, New Mexico’s governor, Michelle Lujan Grisham, said the federal government must examine its fire management practices and how they account for climate change.

“This is a first step toward the federal government taking full responsibility for the largest wildfire in state history, which has destroyed hundreds of homes, displaced tens of thousands of New Mexicans and cost the state and local governments millions of dollars,” she said in a statement.

In the Western United States, wildfires are burning more frequently and more intensely and wildfire seasons are growing longer, narrowing the windows for performing prescribed burns. Recent research has suggested that heat and dryness associated with human-caused global warming are major reasons for the increase in bigger and stronger wildfires.

Lisa Dale, a lecturer at Columbia Climate School, said prescribed burns are the best tools available for reducing the long-term risk from wildfires. They clear away vegetation that would otherwise fuel an unwanted fire and recognize that forests depend on fire to be healthy.

“I hope that the aftermath of this incident doesn’t lead to long-term policy changes that will continue to limit our ability to use this tool,” Dr. Dale said.

She said climate change has made it more difficult to use prescribed fires because fire seasons have increased to seven to eight months from around three months. The growing intensity of fires has also made it more difficult for fire managers to respond.

The Forest Service’s chief, Randy Moore, said last week that the agency would pause its use of prescribed fires on the agency’s lands.

Mr. Moore said that during the pause, the agency would conduct a 90-day review of its protocols and practices for prescribed fires. The pause coincides with the time of year when planned burns are less frequent. More than 90 percent of the agency’s planned fires take place between September and May.

Mr. Moore said the Forest Service oversees an average of 4,500 prescribed fires each year and in “99.84 percent of cases, prescribed fires go as planned.”