This Word Means: Atmospheric river

“When atmospheric rivers pass over land they can cause conditions similar to those of hurricanes with intense and rapid rainfall, cyclone force winds, and significantly increased wave heights,” according to the National Oceanic and Atmospheric Administration (NOAA). For instance, in December 2010, a series of atmospheric rivers hit the US West Coast, producing 11 to 25 inches of rain in certain areas.

Atmospheric rivers can vary greatly in size and strength. But usually, they are 402 to 606 km wide and can be more than 1600 km long, NOAA said.

Although atmospheric rivers occur all over the world, they are most common in the mid-latitudes. “They form when large-scale weather patterns align to create narrow channels, or filaments, of intense moisture transport. These start over warm water, typically tropical oceans, and are guided toward the coast by low-level jet streams ahead of cold fronts of extratropical cyclones,” according to a report by PBS.

One of the most well-known and strongest atmospheric rivers is the Pineapple Express, with moisture transported from the tropical Pacific around Hawaii to the US and Canadian West Coasts. Note that the latest atmospheric river to hit the US is not the Pineapple Express as it originated in the Caribbean, AccuWeather senior meteorologist Tom Kines told Newsweek.

Is climate change impacting atmospheric rivers?

With global temperatures soaring, more water is evaporating into the air. Warmer air can hold more water vapour — for every 1 degree Celsius rise in average temperature, the atmosphere can hold about 7% more moisture. This makes storms more dangerous as it leads to an increase in precipitation intensity, duration and/or frequency, which ultimately causes severe flooding across the world.

Jason Cordeira, associate professor of meteorology at Plymouth State University, told CNN, “So, an atmospheric river, which is defined as a region of water vapour, will likely become more intense. Their frequency may not be more common, but their intensity could become larger.”

A 2018 study by the National Aeronautics and Space Administration (NASA) revealed that atmospheric rivers would be “significantly longer and wider than the ones we observe today, leading to more frequent atmospheric river conditions in affected areas”.

It also said that the frequency of the most intense atmospheric rivers would likely double.