Most residents of the West Coast are all too familiar with the weather phenomena known as an Atmospheric River. Living in the path of an Atmospheric River is like being in the target of of an enormous water vapor firehouse three hundred miles long. It’s a very soggy experience. Now we learn they also comes with very destructive winds.
By CHRISTOPHER JOYCE
Atmospheric rivers are famously wet. But atmospheric scientist Duane Waliser has done some new research that shows they're also remarkably windy.
Waliser studied two decades of storms around the globe at mid-latitudes — that is, outside the tropics. When he focused on the very windiest — the top 2 percent — he found that "atmospheric rivers are typically associated with 30 and even up to 50 percent of those very extreme cases." Atmospheric rivers were also responsible for almost that percentage of the very wettest storms, too.
But the windiness was surprising. Waliser found that winds during an atmospheric river are typically twice the speed of the average storm. He says emergency responders need to know that.
If you're unfamiliar with atmospheric rivers, or are wondering if that's just a fancy name for "rain", they're actually a unique movement of moisture through Earth's atmosphere, responsible for most of the horizontal transport of water vapour outside the tropics.
These suspended moisture plumes, which can stretch 400 to 600 km wide (250 to 370 miles), have been linked to all seven floods on California's Russian River between 1996 and 2007, and likely played a role in the 'Snowmageddon' event that blanketed the East Coast in 2010.
All 10 of Britain's largest floods since the 1970s have also been attributed to atmospheric rivers,
"This has been a very active winter, atmospheric river-wise," Jeff Zimmerman from the NWS, who wasn't involved in the study, told NPR.
While atmospheric rivers are naturally occurring phenomena, climate change is expected to intensify the severe precipitation events caused by atmospheric rivers in the future, because of increased evaporation rates and greater atmospheric water-holding capacity.
"The current situation in California - specifically, the dramatic swing from extreme drought to water overabundance and flooding - is indeed a preview of California's likely climate future," one of the team, climate scientist Daniel Swain from UCLA, told Mashable.
California is now experiencing its worst storm yet — with the potential to reshape its history.
By Eric Holthaus
California’s levee network constrains the flow of water as it leaves the mountains of the Sierra Nevada and makes its way toward the Delta region near Sacramento. Overwhelming this system could bring a flood that, according to a study from the United States Geological Survey in 2011, could inundate hundreds of square miles and cost hundreds of billions of dollars, knocking out the water supply for two-thirds of Californians in the process; it would be the worst disaster in American history. That study, referred to as the “ARkStorm” scenario, was designed to anticipate the impact of a flood with an expected return period of about 300 years, similar to the one the region last experienced in 1862. A 2011 New York Times Magazine article about that scenario used the word “megaflood.”