The wild rivers above California

Atmospheric rivers are meteorological phenomenon that we humans only discovered in 1998 and which supply about 30-to-50 percent of California's annual precipitation. In the NOAA satellite image above, the atmospheric river is visible as a thin yellow arm, reaching out from the Pacific to touch California. Or, more evocatively, reaching out to slap California silly with a gushing downpour.

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.

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.

As you might guess, climate change is also involved. Evidence suggests that warming global temperatures could increase the frequency of atmospheric rivers. That, combined with the 200-year event expected soon and the fact we're learning so much much more about these storms, means that you should expect to hear the phrase "atmospheric river" more often.

Scientific American has two interesting stories on the phenomenon right now. The first, which I quote from above, is a blog post by Mark Fischetti. The second is a much longer feature story that gets into the forces that cause these storms and the climate change connection.


    1. It could be that there is a correlation with solar maximum cycles. In 1862, the west coast of North America was subjected to the largest recorded so called ARK storms, for nearly a month straight. Coincidentally, 1859 was the year of the Carrington event–a repeat of either event will be difficult to cope with…

  1. In California we’ve used the term “Pineapple Express” to refer to this phenomenon for a lot longer than since 1998: a whole series of storms with lots of rainfall over a period of weeks. We rely on most of that water winding up as snow in the Sierra Nevada, where it melts at a nice steady rate so we have plenty of water in the dry season (which is bone dry: virtually no rain at all from mid-May to mid-October). If that winter precipitation winds up as mostly rain instead of mostly snow, Sacramento may be in serious trouble in wet winters.

    1. Agreed, it seems like we’ve been watching these on satellite for years.  Usually they move around and don’t flood one spot, but every once in a while they stay for a few days or weeks and disaster happens.

      Native Americans in the area do seem to have a lot of flood stories, I’ve noticed.  

  2. My one major worry for Southern California: With weather patterns being grossly changed by Global Warming, if a hurricane from south of San Diego were to hit the city, it would be catastrophic!  Everything is focused for earthquake-proofing,  not flood/high wind proofing.  And the outlying suburbs would be pretty much wiped out.  -*(


  3. We’ve had 1.7 inches of rain in the last year.  If the drought holds for another three weeks, that’ll be 3.25 inches in two years.

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