ARkStorm: California officials, scientists dispel rumors of impending megaflood

Winter storms, and particularly strong consecutive ones, are a normal thing in California, but officials and scientists are advising residents that there is no imminent threat from an impending megaflood like the one described in a recent viral video.

The widely shared video said that an impending flood would be “the worst natural disaster in world history,” but the California Office of Emergency Services said that it was full of misinformation.

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The video describes what is known as the “ARkStorm,” a portmanteau of “atmospheric river” (a type of weather system common in California), with the “k” and “storm” for a so-called “once-in-a-thousand-years” storm.

The weather event is a hypothetical disaster scenario studied by climate scientists and the U.S. Geological Survey in 2011. The report created by the group aims to study plausible widespread flooding on a level seen only a few times in recorded history, with the last time being in the winter of 1861-62.

Known as the “Great Flood of 1862,” flooding resulted from almost two months of continuous rain across the state at a time when major dams, levees, canals and other water distribution systems were not yet in place to manage so much precipitation at once.

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While the 1862 flood is the largest flooding event in California’s modern history, climate scientist Daniel Swain, who was part of the ARkStorm study, said on his website that there is “evidence from coastal and bay river sediment deposits of multiple larger events in the past millennium.”

Another event at that level could cause more damage than a large-magnitude earthquake that happens near major cities, Swain said.

The viral video that appeared in January, however, took the scientific study and made claims that the ARkStorm was likely to happen in the next few decades, and a larger conversation started saying that it would occur this week, which Swain said is not true.

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A CalOES spokesperson said that, while large storms and regular flooding occur in the state, the information in the viral video is not true and that residents have nothing to fear.

Swain says that ongoing studies of the ARkStorm scenario now account for recent climate change and new scientific advances that could better define what that storm and flooding would look like — if it ever does happen.

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