A warmer world means a greater risk rain lands on snow, triggering floods

Enlarge / Riverfront Ave. in Calgary during the Alberta floods in 2013. (credit: Ryan L. C. Quan / Wikimedia)

In June 2013, Keith Musselman was living in the Canadian Rockies when the nearby Bow River flooded. "We were in a valley, so we were stuck for about five days," Musselman told Ars. "The community was devastated."

The flood was one of the costliest and most devastating natural disasters in Canada's history, resulting in five deaths and more than 100,000 evacuations and causing extreme property damage. Heavy rainfall falling on late snow in the mountains had overwhelmed rivers and reservoirs, and Musselman, a hydrologist, realized that this kind of rain-on-snow flooding wasn't properly understood.

"Forecasters have a good handle on what happens when rain falls," he says. "But when that rain falls in mountains where there's deep snow, we don't have a good handle on what the flood volume will be."

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