RED LODGE, Montana (AP) – Just three months ago, the Yellowstone region, like most of the west, was being dragged by a prolonged drought with little snow in the mountains and forest fire scars at Red Lodge a year ago when the area was affected by 105. – Grade Fahrenheit (40.5 Celsius) heat and fire.
Rivers and streams flooded this week with much higher and faster water than even the rare 500-year reference flood. Weather-beaten residents and government officials rushed to save homes, roads and businesses.
Most ephemeral natural forces with some connections to long-term climate change combined to cause drought change in the flood, scientists said.
It was a “weird weather” textbook case, said Red Lodge resident and senior assistant scientist at the National Snow and Ice Data Center. Her cut hair had a sweat band and was covered in mud from head to toe to help residents clean up the flooded areas.
But these were unique conditions in the interior of the northwest, scientists say. Most of the west does not have much snow and will continue to struggle with drought.
In the Yellowstone area, after a winter with light snow, it has finally accumulated a couple of months ago, wet and cold, probably thanks to the natural weather event La Nina, which lifted the snow cover to the mountain above normal levels. The snow fell so hard on Memorial Day weekend that people had to leave their camping gear and leave the park while they could, said Tom Osborne, a hydrologist who has spent decades in the area.
Things looked good. The drought did not break completely; in fact, Thursday’s national drought monitor still puts 84% of Montana in unusually dry or full-blown drought conditions, but it was better. Then came something too wet. Heavy rains came thanks to a warmer-than-normal Pacific water-laden water-laden atmosphere. And when it spilled, it melted. The equivalent of nine inches (23 inches) of rain flowed down the slopes of the Montana Mountains in some places. Half or more was from melting snow, scientists said.
All the rivers and streams reacted the same way: “They fired at levels far beyond anything ever recorded,” Osborne said. “Hydrologists know there is nothing that causes more severe flooding in the west than a rain event on snow.”
A stillwater river near Absarokee, where Osborne lives, normally flows at 7,000 cubic feet (200 cubic meters) per second during a moderate flood and runs at 12,400 cubic feet (350 cubic meters) per second in a 100-year flood. , He said. A flood once every 500 years would mean that water was sweeping at 14,400 cubic feet (410 cubic meters) per second. Preliminary figures show that on Monday, it reached 23,700 cubic feet (670 cubic meters) per second, the equivalent of stacking three moderate floods on top of each other, according to Osborne.
“Many of these roads have existed for decades and had not seen any kind of flood damage like the one we saw,” said Lance VandenBoogart, a meteorologist with the National Meteorological Service.
The storm’s target hit the eastern end of the Custer Gallatin National Mountain Forest, pouring five inches of rain at some points.
La Nina conditions occur when parts of the equatorial Pacific Ocean cool, changing global weather patterns. Although La Nina may be drying up in the southwestern United States, it may increase snow and rain elsewhere in the northwest and may have helped pack more snow to the tops of the Yellowstone Mountains, according to Upmanu Lall, director of the Columbia Water Center in Columbia. University.
And while Oregon, Washington, Idaho and Montana had heaviest snowfall from a cold, humid spring, areas south of it were extremely dry with late spring anemic snow, the climate scientist said. UCLA and Western time expert Daniel Swain.
Then an “atmospheric river” (long regions flowing into the sky moving large amounts of water) entered the area and poured rain into the snow at a time when the weather was warm. This rain came from the North Pacific, where water and air were unusually warm and warmer air held back more rain due to basic physics, Swain said. That’s a small connection to climate change, he said.
In the long run, climate change is shrinking the snow cover in the West, according to Guillaume Mauger, a research scientist with the University of Washington’s Climate Impact Group.
“With climate change, we expect less snow and we expect the melting season to be shorter,” Mauger said.
But spring did not follow that pattern in the long run.
“What’s extraordinary is the combination of that high layer of snow that accumulated in April and May, along with this rainy event and the warmer conditions,” Lall said. “That’s where the flood comes from.”
Lall said an atmospheric river that brought moisture from the Pacific “is a little harder” to link to climate change.
Nina could have played a role in several ways. Although La Nina has been like this throughout the past, “never before in human history have we seen persistent La Nina events with such warm global temperatures. This is a unique combination, “said Swain.” We already know that Nina increases the risk of flooding in some places. It increases the amount of active weather in some places. can overfeed “.
“So you really can’t say it’s one thing or the other,” Swain said. “It’s really both. It’s natural and unnatural together.”
A year ago, Montana climate scientists created the Greater Yellowstone Climate Assessment and warned of rain and snow events like this, said lead co-author of the report Cathy Whitlock, a professor of Earth sciences at Montana State University.
But the real-life flood disaster was much worse, he said.
“Who could have predicted that houses would enter rivers and bridges would be destroyed,” Whitlock said. “It’s much worse than you think. And it’s partly because the infrastructure isn’t set up for extreme weather events.”
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Borenstein reported from Kensington, Maryland; St. Phillis of St. Louis.
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