It was around this time last year that an atmospheric river was singled out as the culprit responsible for causing massive flooding in the U.K. New Scientist posted a chart of it.
Now California is getting hammered by another atmospheric river shown in yellow here:
An atmospheric river is a narrow conveyor belt of vapor about a mile
high that extends thousands of miles from out at sea and can carry as
much water as 15 Mississippi Rivers. It strikes as a series of storms
that arrive for days or weeks on end. Each storm can dump inches of rain
or feet of snow. For more details, see this feature story that Scientific American has just published, written by two experts on these storms.
Scientists discovered atmospheric rivers in 1998 and have only recently characterized them fully enough to allow forecasters to warn of their arrival.
They can strike the west coasts of most continents, but California
seems to be a prime target. As many as nine small atmospheric rivers
reach the state each year, each lasting two to three days, including the
famous “pineapple express” storms that come straight from the Hawaii
region of the Pacific Ocean. Ironically, although the storms are
dangerous, they are also vital; they supply 30 to 50 percent of
California’s rain and snow—in the span of about 10 days a year.
The real scare, however, is that truly massive atmospheric rivers that
cause catastrophic flooding seem to hit the state about once every 200
years, according to evidence recently pieced together (and described in
the article noted above). The last megaflood was in 1861; rains arrived
for 43 days, obliterating Sacramento and bankrupting the state. The
disaster is largely forgotten, but the same region is now home to more
than six million people. Simulations of a 23-day storm
there indicate that more than $400 billion of damage and losses would
occur, far surpassing the $60 billion estimates for Hurricane Sandy’s
effects. New research also shows that climate change may make these
storms more likely to occur.
Vancouver Island winds up on the receiving end of these atmospheric rivers just about every winter. They're why we're the wettest region by far in Canada. Nearby Uclulet holds the Canadian record for the wettest town with 490 mm. of rain in one day. Hartley Bay, just around the spit from where Enbridge CEO Stephen Harper wants to build his supertanker port, averages just under 4600 mm. of rainfall per year, about 15 feet. Henderson Lake, between Uclulet and Port Alberni, has recorded 30-feet of rain in one year. Fortunately we have a rocky, mountainous terrain which facilitates natural runoff and minimizes the flood hazards to which the Lower Mainland is susceptible. Touch wood.