ARK Storms in California. A Bigger “Big One” is Coming

August 18, 2022

We’ve seen research published in the last week detailing the newest analysis of what an epic “Pineapple Express” storm on the west coast might look like. They’re known as “Ark Storms” – (meaning Atmospheric River Thousand Year event).
We know that a big one happened in 1861, that, had it happened today, would be an unprecedented disaster. Climate change suggests that a repeat would be an off-the-chart catastrophe.

I had asked author Daniel Swain about this exact topic when I interviewed him in January of this year, (because of course I did) and he gave me what was, at the time, a preview of the results, above.

Below, press release from UCLA, where Swain also holds a position.


Scientists call it California’s “other big one,” and they say it could cause three times as much damage as a major earthquake ripping along the San Andreas Fault.

Although it might sound absurd to those who still recall five years of withering drought and mandatory water restrictions, researchers and engineers warn that California may be due for rain of biblical proportions — or what experts call an ARkStorm.

Daniel Swain, a UCLA climate scientist, said hydrological and forecast data used by the corps must be updated.

“The Army Corps’ estimates of the impacts of an extremely serious weather event … are categorically underestimated,” he said. “That’s because we only have about a century of records to refer to in California. So, they are extrapolating in the dark.”

As an example, Swain said until recently it was thought a flood the magnitude of the 1861-1862 event was likely to occur every 1,000 to 10,000 years. New research has changed that view considerably, Swain said.

“A newer study suggests the chances of seeing another flood of that magnitude over the next 40 years are about 50-50,” he said.

Here, meteorologist Mathew Cappuci gives a vivid video wrap of the research, and on the next page, Park Williams adds some detail.


Many Californians fear the “Big One,” but it might not be what you think. 

It’s not an earthquake. And it isn’t the mega drought. It’s actually the exact opposite. 

A megaflood. 

A new study by Science Advances shows climate change has already doubled the chances of a disastrous flood happening in California in the next four decades. And experts say it would be unlike anything anyone alive today has ever experienced.

Daniel Swain, a climate scientist with UCLA and a researcher involved in the study, describes a megaflood as, “a very severe flood event across a broad region that has the potential to bring catastrophic impacts to society in the areas affected.” He said a megaflood is similar to the 1,000-year flash flood events seen this summer in the St. Louis area and Kentucky, but across a much wider area, such as the entire state of California.

These massive floods, which experts say would turn California’s lowlands into a “vast inland sea,” might have previously happened once in a lifetime in the state. But experts say climate change is increasing the likelihood of these catastrophic disasters, causing them to occur more like every 25 to 50 years.

Sacramento 1861

3 Responses to “ARK Storms in California. A Bigger “Big One” is Coming”

  1. Brent Jensen-Schmidt Says:

    OH shit!
    Clever terminology!

  2. rhymeswithgoalie Says:

    flood = rain + terrain

    I often point out that, since humans excel at modifying terrain, the marker for climate change is in the rain measurements. That is, you can get a record flood with normal rain levels if more is paved or blocked. (Conversely, clever runoff management can mitigate what might happen naturally.)

    In the case of the rain levels in 1861-62, so much of California has been cleared and/or paved that we should expect it to be worse flooding for the same amount of rain. On top of that much of the state has greater areas of wildfire scar than a decade or so ago.

    Are we having fun, yet?

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