Underestimated threat of flooding rains, landslides, erosion

DOE study: snow-dominated mountain regions face more risk

New research published in the journal Nature shows that most mountain regions in Western North America are more vulnerable to extreme rainfall that can “trigger landslides, floods and severe erosion.”

Unlike previous research into extreme precipitation events, the Earth and Environmental Sciences research conducted by Lawrence Berkeley National Laboratory focused on precipitation falling as either rain or snow, and subsequent impacts downstream.

“We’ve known for decades that as the atmosphere warms, it can hold more water vapor and that water will eventually (fall) as precipitation,” said lead author Dr. Mohammed Ombadi, “Our estimate of that was… about 7 percent with each degree (Celsius) of warming.”

The Clausius–Clapeyron relation shows the water-holding capacity of the atmosphere increasing 7 percent per 1 degree Celsius of warming.

But the increase in rainfall as the warming atmosphere grows more saturated greatly exceeded their expectation. “…If you single out the liquid part, and look at rainfall extremes separately, that rate is almost more than doubled to 15 percent,” said Ombadi.

The research suggests a “linear rate of increasing extreme rainfall with future warming. The most current estimates put the world on a path to heat by up to 3 degrees Celsius by 2100, which would bring a 45 percent increase of extreme rainfall over many mountain areas.”

“…Every degree matters (as) We see this amplified increase in rainfall extremes over most high-elevation regions and mountains of snow-dominated regions across the northern hemisphere. And we see that mountain ranges in Western North America are at greater risk than other mountain ranges,” the study’s authors highlight.

Water cycle changes land

Ombadi said that more intense rainfall can also accelerate “parts of the geological cycle, crumbling more rock faster and moving more sediment and debris through rivers and lakes and into the oceans.”

Another hypothesis is that more heating evaporates soil moisture, which intensifies rainfall even further.