Earth Notes: Rain-On-Snow Flood Risk

Feb 26, 2020

When a warm storm front moves over a snow-capped mountain range, floods often follow. These events aren’t common on the Colorado Plateau, where winter precipitation usually falls as snow. But scientists say that’s going to change as the world continues to heat up. 

The snowpack in the higher elevations near Humphreys Peak in Jan. 2017.
Credit Josh Langdon/Kachina Peaks Avalanche Center

Researchers at the University of Colorado-Boulder ran simulations of the United States’ future climate in the supercomputer at the National Center for Atmospheric Research. They discovered some areas of the country, such as the Pacific Northwest, will see fewer floods from rain-on-snow events. That’s because those regions will have less snow on the ground in a warmer world.

But it’s a different story in the high elevations of the Colorado Plateau, where deep snowpack will still accumulate. The scientists found, in some areas, flooding caused by rain-on-snow events could more than double by the end of the century, if climate change continues unchecked.

In February 2017 one of these events caused a record deluge on the Feather River in the Sierra Nevada, another area predicted to have more floods. Engineers opened the spillway on Oroville Dam, only to watch the water chew through the concrete. Nearly 200,000 people were evacuated for fear the dam would collapse. It held, but the flood caused a billion dollars in damages.

A future with more flooding isn’t inevitable. The research team is now running dozens of computer simulations that consider policies we might adopt to slow the pace of climate change. The results may show us what we can do to avert catastrophic floods before they begin.