Explainer | What is an atmospheric river? Here’s why British Columbia is experiencing flooding and landslides

The torrential rains that have battered British Columbia in recent days, causing landslides and flooding, closing roads, and stranding and displacing thousands, are being driven by an atmospheric river.

Atmospheric rivers are long, narrow bands of moisture in the atmosphere that carry water from the tropics and subtropics toward the poles.

in a May 2019 Feature About the phenomenon, Star reporter Ainslie Cruickshank wrote:

To the naked eye, no more than a sea of ​​wispy clouds, atmospheric rivers carry about 90 percent of the water vapor that is carried toward the north and south poles through the mid-latitudes, in the northern hemisphere, which includes the area covering Canada. provinces.

At their finest, they soak parched landscapes and replenish depleted water sources. In California, about half of the state’s annual precipitation can come from atmospheric rivers.

But a strong atmospheric river can carry 25 Mississippi rivers of water vapor, and when it hits land, it releases tremendous rains that could last for days and trigger devastating landslides, floods, and fatal avalanches.

BC is no stranger to atmospheric rivers: between 25 and 30 reach the coast each year, but studies show that climate change is making them bigger and more dangerous.

“As climate change occurs, the earth’s temperature warms,” ​​said Duane Waliser, principal scientist at NASA’s Jet Propulsion Laboratory and co-author of a study on atmospheric rivers and climate change. “Basically warm air holds more moisture than cold air.” D

The 2019 models indicate that the typical atmospheric river of the 21st century will be approximately 25% wider (855 km vs 700 km) and 25% longer (5,400 km vs 4,300 km) than those of the 20th century.