Climate change may be impacting atmospheric rivers

A new study, just published in the American Geophysical Union, indicates that climate change may be making atmospheric river events more intense and frequent. The warming of the world's oceans is likely the key reason.

Atmospheric rivers (ARs) are long, narrow bands of highly concentrated water vapor and are responsible for some of the heaviest precipitation events in the world, including the one in the U.S. West Coast.

Several AR events have already inundated the state of California since the start of this past winter, resulting in extreme rainfall and massive amounts of snow in the mountains. These events have nearly wiped out the drought in a large portion of California, but they have also caused deadly flooding, mudslides and avalanches that will cost millions of dollars.

“Atmospheric rivers are the hurricanes of the West Coast when it comes to the public’s situational awareness,” said F. Martin Ralph, an atmospheric scientist at Scripps Institution of Oceanography at UC San Diego and a co-author on the new study.

In order to better educate the public and media about the potential threats from these AR events, the research team developed an intensity scale that ranked AR events from 1 to 5, with 5 being the strongest.

"People need to know when they’re coming, have a sense for how extreme the storm will be and know how to prepare, said Ralph. “This scale is designed to help answer all those questions.”

During drought conditions, weaker AR events can be more beneficial to a region, bringing much-needed drought relief in the form of steady, soaking rainfall. However, more intense AR events, such as those in categories 4 or 5, can cause disaster in the form of deadly and damaging flooding, mudslides and avalanches.

According to the study, the most intense AR events are less common than the weaker events and on average only occur once every 2-3 years globally. The strongest AR events are also less likely to make landfall and usually lose intensity more rapidly once they move inland compared to less intense events.

Intense AR events are also more common during strong El Niño years. However, the recent onslaught in California has occurred during the weakening phase of a La Niña.

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