Ark Storm

Gwen flicked through the paper. She paused as she recognized the byline. Curious, she leaned back, sipped her coffee, and read.

Would you rather die under tons of falling rubble or be washed to your death by a ten-foot wall of water? Not a question any one of us wishes to entertain, yet here in California you are about as likely to be hit by an ARk Storm as by the “shakeout quake.” Yet few of us have ever heard of an ARk Storm. It is the big quake that is the stuff of our nightmares, but now we have a new nightmare scenario lurking on the horizon.

What is an ARk Storm?

An ARk Storm is a kind of supercharged West Coast Winter Storm caused by Atmospheric Rivers dumping huge rainfall as they make landfall. Every winter season several ARk Storms make landfall and dump heavy rains. The ARk Storm 1000 is the big one that threatens to hit every one to two hundred years or so.

A team of 117 scientists, engineers, public policy and insurance experts under the umbrella of The Multi-Hazards Demonstration Project have worked for two years to create the hypothetical scenario of what such a storm could be, and what damage it would wreak across the State of California.

ARk Storms take their name from what’s known by researchers as “Atmospheric Rivers,” a term coined as a result of last-generation satellite imagery that shows these bands of moisture flowing several kilometers above the earth. ARs are giant ribbons of moist air, at least 2000 kilometers long and several hundred kilometers wide. They flow in the lower troposphere, normally about ten kilometers up, where winds with speeds in excess of 12.5 meters per second can carry as much water as the Amazon River.

Most people looking up on a clear day would never think that just a few miles above their heads a huge river of moisture hundreds of miles wide could be coursing through the atmosphere.

In an ARk Storm 1000 scenario, this river, described by the head of the ARk Storm Unit as “like Forty Mississippis,” races from the tropics toward the west coast of the US, then hits, and keeps on hitting. The Storm Door opens and fails to close. The rains start and a biblical scenario plays out.

The ARk Storm 1000 would be predicted to come ashore at 125 mph in Los Angeles County. This is a storm so intense it has been described as “like Hurricane Katrina pushed through a keyhole.” It would cause widespread flooding in the Sacramento-San Joaquin Delta. Fifty levees could be breached. Some one and a half million residents in inland and delta regions would be forced to evacuate. The model estimates that up to one quarter of all homes in California would have flood damage to the tune of 400 billion dollars. Because the flood depths in some areas could realistically be of the order of ten to twenty feet, without effective evacuation of up to one and half million people there could be substantial loss of life. High winds would cause further damage of around five billion dollars. Huge waves would damage coastal property. Landslides would be extensive, causing around one billion dollars worth of damage. The overall cost, adding in economic disruption to the State of California, is estimated to be in the region of one trillion dollars. That is four times as much as the shakeout earthquake. And only around 12 percent of California property is insured.

Has such a storm happened before?

Major ARk Storms have hit California on a regular basis. The last huge one was in 1861–62 when it rained continuously for forty-five consecutive days. Witnesses describe a “flying river” washing away livestock and humans. That storm caused flooding of biblical proportions, turning the Sacramento and San Joaquin valleys—a region around three and a half million acres, incidentally—into a lake. That storm bankrupted the state. And it gets worse.… The geological record shows six megastorms more severe than 1861–62 hit in California in the last 1,800 years. There is no reason to believe such events will not recur.

What caused the 1861–62 ARk Storm?

The atmospheric mechanisms behind the storms of 1861–62 are unknown; however, the storms were likely the result of an intense atmospheric river, or a series of atmospheric rivers, striking the U.S. West Coast. With the right preconditions, just one intense atmospheric river hitting the Sierra Nevada mountain range east of Sacramento could bring devastation to California.

Can we predict an ARk Storm?

The Hazards team’s answer is: “to some extent.” Unlike for earthquakes, forecasters have the capability to partially predict key aspects of the geophysical phenomena that would create changes in the days before an ARk Storm struck. They concede though that “enhancing the accuracy, lead time, and the particular measures that these systems can estimate is a great challenge scientifically and practically.”

So what can we do to prepare?

The whole ARk Storm Project has been undertaken to enable the State of California to prepare an emergency response plan. We can only hope that it gives us notice.

When might it hit?

The most senior scientist for the Hazards Project notes the coincidence that California’s last big ARk Storm occurred in 1861–62, very close to the last big Southern San Andreas big earthquake in 1857. It appears that both events occur with a frequency of about two hundred years. Which begs the question: Which one will go next?

Gwen finished her coffee, folded her paper thoughtfully. Yeah, hell of a way to go, drowning in earth, or drowning in water. Involuntarily, she shuddered.