A river runs through it. The Gardner River reclaimed it right to meander on June 13th.
SJ Keller, National Geographic, June 16, 2022
Rain falling on snow caused [the recent] floods, events that will become more likely as temperatures warm.
Yellowstone National Park evacuated more than 10,000 visitors on Tuesday after flash floods roared through the park. Roads and bridges washed away, sewage lines broke, and the park’s gateway communities were cut off from roads. Yellowstone remains closed, and the north entrance gate will likely not reopen this season.
Even as scientists and land managers are taken aback by the magnitude of the floods, unprecedented in 100 years of recorded history, they recognize the similarities to the events their data predicted. They just weren’t anticipating them to occur this year.
“As a scientist I would say, well, this is completely in line with what we might expect,” says Cathy Whitlock, a paleoclimatologist and lead author of the Greater Yellowstone Climate Assessment, the first such report ever done on an ecosystem. “As a human being I would say I'm shocked.”
While it will take more research to confirm if climate change made this flood event more extreme, the 2021 Greater Yellowstone Climate Assessment predicts significant changes in precipitation, including when it arrives and what form it will take. Scientists expect more spring rain, less winter snow. The assessment also predicts increasing annual precipitation in Yellowstone National Park.
Changes are already documented in the assessment. Since 1950, spring precipitation in the region has increased by 17 percent in April and 23 percent in May. Snowfall has declined even as overall annual precipitation has increased. That means rather than a slow release of melt water to valleys during the summer months, rainfall tends to combine with melting snow, causing riskier events like the recent flood.
In mid-June, the jet stream carried in exceptionally wet weather dropping rain on the unusually snowy mountains. Warm temperatures helped melt the snowpack. And as temperatures warm, these rain-on-snow events are projected to become more frequent at higher elevations in western North America, while lower snowpack will make them less frequent at low elevations.
Yellowstone’s Superintendent Cam Sholly said during a Tuesday press conference he’s been advised that the flood could be a thousand-year event. One of the highest recorded stream flow measurements for the Yellowstone River was 31,000 cubic feet per second, recorded in the 1990s. Stream flow readings during the recent flood were as high as 51,000 cubic feet per second.
“What happened this week was not anything I was expecting,” says Rodman. June precipitation this year is now at more than 400 percent above average in the parts of Montana and Wyoming that include Yellowstone. “We had rain that went all night and all day and it was kind of torrential. We just don’t get that kind of rain here.” On Monday, she watched from her house in Gardiner, just outside Yellowstone’s north entrance, as park employee housing slid into the Yellowstone River.