Jun 17, 2022 - Energy & Environment

USGS: Yellowstone River flooding was a 1-in-500-year event

Lower Blacktail Patrol Cabin washed away.

The Lower Blacktail Patrol Cabin, which washed away at Yellowstone National Park. Photo: NPS/Jacob W. Frank

The massive flooding that happened at the Yellowstone River this week represents a 1-in-500-year event, the U.S. Geological Survey said Thursday.

Why it matters: The catastrophic flood — which damaged roads and bridges at Yellowstone — has a 0.2% (or 1-in-500) chance of happening in any given year, the USGS said in a news release.

Driving the news: Katherine Chase, USGS hydrologist, said that the peak amount of water flowing in the Yellowstone River at Corwin Springs and Yellowstone River at Livingston was "higher than the 0.2% (or 1 in 500) flood" levels seen during the recent flood event.

  • Chase said the floods have been referred to as rarer than a 1-in-500 event. But "there is the same probability that they could occur in any given year," she said.
  • Meanwhile, the streamflow at the Yellowstone River at Billings was closer to the "1% (or 1 in 100 years) and 0.2% (1 in 500 years) flood."
  • The streamflow data is "provisional" right now until an analysis of the data is finished, the USGS said.

Worth noting: The USGS calculates this information based on historical data, CNN reports.

The big picture: National Park Service officials told reporters Tuesday that the extreme flooding may represent a “thousand-year event."

  • “This isn’t my words, but I’ve heard this is a thousand-year event,” Yellowstone Superintendent Cam Sholly said.
  • He said the highest cubic feet per second (CFS) ratings for the Yellowstone River was recorded in the 1990s at 31,000 CFS.
  • On Sunday night, the CFS rating hovered at 51,000 CFS, he said.

Our thought bubble, via Axios' Andrew Freedman: Climate change is causing an increase in the frequency and severity of heavy precipitation events, and a 2021 climate assessment for Yellowstone warned of more flood threats.

Go deeper ... Yellowstone floods: Photos, video show massive damage

"Unprecedented" rainfall forces Yellowstone to close all entrances

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