Yellowstone floods reveal prediction errors as climate warms

Billings, Mont. (AP) – The Yellowstone National Park area’s weather forecast on the morning of June 12 seemed fairly tame: Warmer temperatures and rain showers would accelerate mountain snowmelt, causing “minor flooding.” areas, but made no mention of danger to humans.

At nightfall, after several inches of rain had fallen on a deep spring snowpack, there were… record-breaking floods.

Torrents of water poured from the mountains. Swollen rivers with boulders and trees crushed by the cities of Montana the next few days. The floods have swept away houses, bridges and the evacuation of more than 10,000 tourists, park workers and residents near the park.

As a cleanup that is expected to take months continues, climate experts and meteorologists say the gap between the destruction and what was predicted underlines a tricky aspect of climate change: Models used to predict storm effects don’t always keep pace with increasingly devastating ones. rain showers, hurricanes, heat waves and other events.

“Those rivers had never reached that level. We literally flew blind and didn’t even know what the consequences would be,” said Arin Peters, senior hydrologist with the National Weather Service.

Hydrological models used to predict flooding are based on long-term historical data. But they don’t reflect the changes in climate that have occurred over the past decade, said meteorologist and Weather Underground founder Jeff Masters.

“Those models will not be sufficient to deal with a new climate,” Masters said.

Another extreme weather event where the models came up short was Hurricane Ida, which hit Louisiana last summer. stranded over the east coast — Parts of Pennsylvania, New Jersey and New York were flooded with unprecedented rainfall that caused massive flooding.

The weather service had warned of a “serious situation” that could turn “catastrophic,” but the forecasted rain of 3 to 6 inches (8 to 15 centimeters) for New York, New Jersey and Pennsylvania was much less than the 9 to 10 inches (23 to 25 centimeters) who fell.

The deadly June 2021 heatwave that scorched the Pacific Northwest was another example. Warmer weather was expected, but no temperatures as high as 116 degrees (47C degrees) to topple previous records and killed an estimated 600 or more people in Oregon, Washington State and western Canada.

Yellowstone’s surprise floods sparked an overnight battle to close down roads and bridges that were swept away by the water, plus rushed evacuations that left some people missing. No one died, somewhat miraculously, as more than 400 homes were damaged or destroyed.

When rock slides began to form in Yellowstone from the rain, park rangers closed off a well-used road between the town of Gardiner and the park’s headquarters in Mammoth Hot Springs, Wyoming. It later washed out in many places.

The rain and snow melt were “too much too fast and you’re just trying to stay out of the way,” Yellowstone Deputy Chief Ranger Tim Townsend said.

If the road hadn’t been closed, “no doubt we would have had fatalities,” said Park Superintendent Cam Sholly.

“The road looks all right and then it’s like an 80-foot drop straight into the river,” said Sholly. “If someone was driving in the rain at night, they wouldn’t have seen it and could have stopped.”

Rock Creek, which runs through the town of Red Lodge and is normally quiet and sometimes ankle-deep, became a churning river. When the weather service issued a flood warning for the creek, the water had already overflowed and bridges had begun to fall.

By the time the warning was issued, “we already knew it was too late,” said Scott Williams, a commissioner for Carbon County, Montana, which borders Yellowstone.

Red Lodge resident Pam Smith was warned of the flooding by something that hit her basement before dawn. It was her clothes dryer, floating in the water that poured through the windows.

In an effort to preserve souvenirs, Smith slipped on the wet kitchen floor and fell, shattering a bone in her arm. She recalled holding back tears as she trudged through the water with her partner and 15-year-old granddaughter to reach their pickup truck and get to safety.

“I went blank,” Smith said. “I was angry and thought, ‘Why didn’t anyone warn us? Why didn’t there be a knock on the door? Why didn’t the police come over and say there’s flooding, you have to get out?’”

Local authorities say sheriffs and others knocked on the door in Red Lodge and a second community that flooded. But they acknowledged that not everyone was reached as countless rivers and streams overflowed, inundating areas never before inundated.

While no weather event can be definitively linked to climate change, scientists said the flooding in Yellowstone was consistent with changes already documented in the park as temperatures warmed.

Those changes include less snowfall in the middle of winter and more precipitation in the spring — setting the stage for flash flooding when rain falls on the snow, said climate scientist Cathy Whitlock of Montana State University.

Warming trends mean spring floods will increase in frequency — even as the region suffers from prolonged drought that keeps much of the rest of the year dry, she said.

Masters and other experts noted that computer modeling of storms has become more sophisticated and generally more accurate than ever. But extreme weather is naturally difficult to predict, and as such events become more frequent, there will be many more chances for forecasters to be wrong.

The rate of the most extreme rainfall events has increased by a factor of five, Masters said. So an event with a 1% chance of happening in any given year — commonly called a “one in 100 year” event — now has a 5% chance of it happening, he said.

“We’re literally rewriting our weather history book,” said Jason Furtado, a professor of meteorology at the University of Oklahoma.

That has widespread implications for local authorities and emergency services who rely on weather reports to guide their response to disasters. If they are not warned, they cannot act.

But the National Weather Service also strives to avoid unnecessary alarms and maintain public confidence. So if the service’s models show a small probability of disaster, that information is likely left out of the forecast.

Weather officials said the agency’s actions with the Yellowstone flooding will be analyzed to determine if changes are needed. They said early warnings that river levels were rising helped officials prepare for and prevent loss of life, even if their advisories didn’t predict the severity.

Computer-based forecasting models are regularly updated to account for new meteorological trends due to climate change, Peters said. Even with those refinements, events like the Yellowstone flooding are still considered low probability and so often won’t make predictions based on what the models say will most likely happen.

“It’s really hard to balance the feeling that you have that this could get really bad, but the chances of it getting really bad are so slim,” Peters said. He added that the dramatic switch from drought to flooding was difficult even for meteorologists to reconcile, calling it “weather whiplash.”

To better communicate the potential for extreme weather, some experts say the weather service should change its forecasts to inform the public about dangerous, low-probability events. That can be achieved through more detailed daily forecasts or some sort of color-coded alert system.

“We’ve been slow in providing that information,” said atmospheric scientist Gary Lackmann of North Carolina State University. “You put it on people’s radars and they can think about it and it can save lives.”

Hanson reported from Helena, Montana.

Follow Matthew Brown: @MatthewBrownAP

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