Q: What is an atmospheric river?
A: Join me in song.*
—three-four!
Don’t know why it’s raining this way
All this water and skies are so gray
Pack an umbrella; wear some Gore-Tex
You haven’t seen the worst of it yet
I wanna knoooooow you won’t tell me
This rain’s gonna stay
Atmospheric river, drops on us the water
Atmospheric river, pours even more water
Washing us down, washing us down
Has this song been stuck in the heads of every Californian for a month? Kind of. But they know the drill. Atmospheric rivers, the so-called Pineapple Express, are a feature of almost every coastline in the world—causing half the extreme wind events and dropping more than half of the water those coasts see in rainfall. They can be 300 miles wide and 1,000 miles long, and even though just 2.8 percent of the rainfall hours in California between 2004 and 2010 were atmospheric river hours, they dropped 60 percent of the state’s rain.
More hyperbolic stats? Sure, we got ‘em. More snow in a day than Boston got all winter. More rain in eight hours in Palm Springs than in the previous eight months. San Jose breaks a century-old rainfall record. Sonoma County got 20 inches of rain in two days (and yes, there were floods). Half of California’s water supply is now frozen as snow in the Sierras (that’s good; it’s literally cold storage).
I don’t know why you’re raining so hard
All this wind makes you a blowhard
You’ve dropped an ocean, a flood, a deluge
A lot of water that, sure, we can use
I wanna knoooooow you won’t tell me
This rain’s gonna stay
Atmospheric river, drops on us the water
Atmospheric river, pours even more water
Washing us down, washing us
What causes them? The “river” part isn’t just a metaphor; warm, moisture-laden air in the troposphere—from the ground to between 6 to 12 miles up— over the tropics blows eastward. The flow eventually hits mountains (in this case, the Sierras) that deflect it upward, where the air cools off—and drops all that moisture. The key number is called Integrated Vapor Transport: the amount of water getting pushed. According to a recently devised scale, any storm that moves more than 250 kilograms of water per meter per second and lasts more than a day is an atmospheric river.
Soak me, spatter me, splash me, splatter me
Till I can’t, till I can’t, till I can’t take no more
Drop down more water, atmospheric river
Rain down more water, atmospheric river
Washing us down, washing us down
I don’t know why you snow and you rain
Wish my galoshes would fit on my brain
Fifty inches of rain is a slog
And now I still have to go walk the dog
While it’s true that atmospheric rivers bring floods, mudslides, sinkholes, and a generalized emotional graying of the Golden State, they also are the monsoons that typically end California’s dry seasons and break the state’s frequent droughts. But even that upside-down might be turning into a frown. Climate change means that atmospheric rivers are getting warmer at higher altitudes, dropping rain instead of snow. Without that snowpack, the state’s people and agriculture don’t have enough water. The rivers will flow, but the droughts won’t end.
Atmospheric river, don’t just drop water
Atmospheric river, we need more snow—a lot-ter
Keep washing us down, washing us down.
*With apologies to Al Green, Mabon Lewis Hodges, Talking Heads, and music generally.