After two weeks of wildfires, flooding in New Mexico this weekend caused severe flooding and debris flows near Ruidoso.
Dark water, blackened by soot and ash from the South Fork and Salt fires, rushed mountain gorges into the city, turning Highway 70 into a river and overturning a fuel tanker, according to videos posted on social media. Homes and businesses suffered damage and emergency services reported 77 water rescues.
“It’s going to be a long road to recovery,” said Kerry Gladden, a public information officer for the village of Ruidoso. The monsoon season usually starts around July 4 and this year it coincided with two weeks of bushfires, dramatically increasing the risk of flooding. “This will continue to happen every time there is heavy rain,” Ms Gladden said.
While the South Fork and Salt fires last month killed two people and burned more than 25,000 acres, the fire scars left behind could put residents at even greater risk than the wildfires themselves.
Climate change, caused mainly by the burning of fossil fuels, continues to cause an increase in both very intense fires 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 flooding or debris flows as a footnote after the fact, 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 could be more destructive and cause more loss of life than the fire.”
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, an 8-foot-long 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 issued a third evacuation warning: “Go now!” the order said.
Three factors increase the likelihood and danger of flooding and debris flow after a fire: how severely the ground is burned, how intense the rainfall is, and the steepness of the landscape.
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 fire severity has increased in recent decades,” says Luke McGuire, associate professor of geomorphology at the University of Arizona, “is causing an increase in these post-fire risks.”
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 practices have generally minimized natural and prescribed burns, which is the practice of deliberately setting smaller, controlled fires as a preventative measure.
TJ Clifford, BAER team leader 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 burning. 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 floods have already hit the region, debris flows still pose a looming threat. While flooding is like pulling a silk dress through a canal, Mr. Clifford said, a flow of debris, a type of landslide, is like rubbing sandpaper through a canal and moving away anything that bumps into it.
“Post-fire debris flows are different beasts than floods,” says Dr. McGuire. They can cause a variety of problems, often affecting people and infrastructure more severely than a flood, and affecting areas outside a typical floodplain.
Dr. McGuire and his colleagues published a study in Nature Reviews Earth & Environment in May that showed post-debris flows were increasingly recurring. In 68 percent of global locations where debris flows had already occurred, another deluge was likely to occur in the future.
Although Mrs. Smith and her parents’ home has been spared so far, neighbors were not so lucky. Charred trees border the faded driveway, but across the street, river rock chimneys loom over houses flattened by fire. “Our emotions are all over the place,” Ms. Smith said on Sunday. “The Upper Canyon looks devastating.”
The official cause of the fire is still under investigation. The FBI is offering a $10,000 reward for any information that could lead to the arrest of those responsible for starting the fire.
