Flash flooding after New Mexico wildfires highlights climate risks

After two weeks of wildfires, a flood in New Mexico this weekend caused severe flooding and debris flows near Ruidoso.

Dark floodwaters, blackened by soot and ash from the South Fork and Salt fires, rushed through mountain canyons and into the city, turning Highway 70 into a river and push over a fuel tankeraccording to videos posted on social media. Homes and businesses were damaged and emergency services reported 77 water rescues.

“It’s going to be a long road to recovery,” said Kerry Gladden, a community educator for Ruidoso. Monsoon season typically starts around the Fourth of July, and this year it coincided with two weeks of wildfires, greatly increasing the risk of flooding. “This is going to happen every time we get a heavy rain,” Gladden said.

The South Fork and Salt fires last month killed two people and burned more than 25,000 acres, but the burns they leave behind pose an even greater risk to residents than the wildfires themselves.

Climate change, which is mainly caused by the burning of fossil fuels, continues to pose a threat to both fires of high severity that kill vegetation and dry out the soil, and extreme rainfall that produces more precipitation in a shorter period of time. The combination of dry ground and heavy rain increases the likelihood of hazards such as flash floods and debris flows – a dangerous mix of water, mud, boulders and trees after a fire.

“It’s a mistake to treat flash floods or debris flows as an afterthought, rather than a major part of the fire itself,” said Don Falk, a professor of natural resources and fire ecology at the University of Arizona. “It can be more destructive and cause more loss of life than the fire itself.”

On Saturday afternoon, 34-year-old Brittany Smith helped her parents move into their cabin after officials announced the wildfires were under control. Then suddenly their phones lit up with a new emergency alert: a flash flood warning and an urgent evacuation order.

That afternoon, a six and a half feet A wall of dark water flowed through their neighborhood in Upper Canyon, a canyon with steep slopes. On Sunday, as the family tried to return, the village of Ruidoso began a third evacuation warning: “Go now!” the order said.

Three factors increase the likelihood and danger of flooding and debris flows after a fire: how severely the ground is burned, how intense the rainfall is, and how steep the landscape is.

The canopy of trees and vegetation on the forest floor would normally act like a sponge and intercept rainfall. This is especially important during the intense monsoons that occur during southwestern summers.

However, that sponge effect is destroyed by super-hot fires. When the rain comes, the dead soil moves quickly, destabilizing steep slopes.

The effect can last for years. “The fact that there has been an increase in the severity of fires in recent decades,” said Luke McGuire, associate professor of geomorphology at the University of Arizona, “is leading to an increase in these post-fire hazards.”

Karen Miranda Gleason, the public information officer for the Burned Area Emergency Response team, said the areas where the South Fork fire occurred would see high levels of ground burning, although the official burn severity map is not yet available. published.

Over the past 150 years, land management has generally focused on minimizing natural and controlled fires. This involves deliberately setting smaller, controlled fires as a preventative measure.

TJ Clifford, team leader for BAER under the Department of the Interior, said the New Mexico fires would not have severely burned the land if the area had been maintained using land management practices such as forest thinning or prescribed fire. But that could be unpopular.

“Prescribed fire is smoke in the air, and the public doesn’t like smoke in the air,” he said. “It’s very difficult to get support.”

Although flooding has already hit the region, debris flows still pose a looming threat. While flooding is like dragging a silk dress through a canal, Mr. Clifford said, a debris flow, a type of landslide, is like rubbing sandpaper through a canal, carrying away whatever it hits.

“Debris flows after a fire are different beasts than floods,” said Dr. McGuire. They can cause other problems, often affecting people and infrastructure more severely than a flood and affecting areas outside a typical floodplain.

Dr. McGuire and his colleagues published one study in May in Nature Reviews Earth & Environment that showed that post-debris flows are becoming more common. In 68 percent of global locations where debris flows had already occurred, another was likely to occur in the future.

While the home of Mrs. Smith and her parents has so far been spared, neighbors have not been so lucky. Charred trees line their washed-out driveway, but across the street, river-rock chimneys tower over homes destroyed by fire. “Our emotions are all over the place,” Mrs. Smith said Sunday. “The Upper Canyon looks devastated.”

The official cause of the fire is still under investigation. The FBI is offering a $10,000 reward for any information leading to the arrest of those responsible for starting the fire.