Yellowstone River flooding is a 1 in 500-year event, US Geological Survey says

The devastating flooding that occurred along the Yellowstone River this week constitutes a 1 in 500-year event, according to a US Geological Survey (USGS) 新闻发布.

Unprecedented rain and rapid snowmelt in recent days have caused rivers in parts of Montana, 怀俄明州, and Idaho to burst their banks, swallowing bridges and sweeping away entire sections of roadway.

多于 10,000 visitors to Yellowstone National Park have been forced to evacuate. All entrances to the park are expected to remain closed until at least Monday.

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“At two streamgages, Yellowstone River at Corwin Springs and Yellowstone River at Livingston, the peak streamflow was higher than the 0.2% (要么 1 in 500-years) 洪水 (水平),” said USGS hydrologist Katherine Chase in the release.

Farther downstream, “the Yellowstone River at Billings was between the 1% (要么 1 in 100-years) 和 0.2% (1 in 500-years) 洪水,” 根据发布, which notes that streamflow data is “currently being reported as ‘provisional’ until followup analyses of the stream channel and data are completed.”

然而, Chase notes in the release that, “while these floods are often referred to as greater than (or rarer than) 一个 1 in 500-year event, there is the same probability that they could occur in any given year.”

The USGS frequencies are calculated from historical data for the Yellowstone River’s locations. As CNN has reported this week, scientists have shown that climate change is impacting the frequency at which extreme weather events occur, and that trend is expected to continue as the planet continues to warm.

In a three-day period last week, Yellowstone National Park received about two to three times the typical rainfall for the whole month of June, and precipitation this month has already been more than 400% of the average across northwestern Wyoming and southern Montana, according to the National Weather Service.

Yellowstone to remain closed

All five of Yellowstone’s park entrances remained closed Friday as flood recovery and repair efforts are underway in preparation for the park’s reopening, 根据一个 release from the park’s superintendent’s office.

根据发布, the National Park Service does not yet have an estimated reopening date for the entire park — nor an idea of total repair costs. The release outlines an extensive list of repairs needed to roads and infrastructure in each section of the park in order for it to reopen.

“We have made tremendous progress in a very short amount of time but have a long way to go,” Superintendent Cam Sholly said in the release. “All emergency and life safety objectives within the park have been accomplished or stabilized within the first 96 hours of the flood event, without major injury or death.”