An ARkStorm (for Atmospheric River 1000 Storm) is a hypothetical but scientifically realistic "superstorm" scenario developed and published by the United States Geological Survey, Multi Hazards Demonstration Project (MHDP). It describes an extreme storm that may likely impact much of California causing up to $725 billion in damages and repair (most caused by flooding), and affect a quarter of California's homes. The event would be similar to intense California storms which occurred in 1861 and 1862.

The name ARkStorm is also meant to be drawn as a parallel to the biblical Noah's Ark story.

The Central Valley experiences hypothetical flooding 300 miles long and 20 or more miles wide. Serious flooding also occurs in Orange County, Los Angeles County, San Diego, the San Francisco Bay area, and other coastal communities. Windspeeds in some places reach 125 miles per hour, hurricane-force winds.

Across wider areas of the state, winds reach 60 miles per hour. Hundreds of landslides damage roads, highways, and homes. Property damage exceeds $300 billion, most from flooding. Demand surge (an increase in labor rates and other repair costs after major natural disasters) could increase property losses by 20 percent.

Agricultural losses and other costs to repair lifelines, dewater (drain) flooded islands, and repair damage from landslides, brings the total direct property loss to nearly $400 billion, of which $20 to $30 billion would be recoverable through public and commercial insurance.

Power, water, sewer, and other lifelines experience damage that takes weeks or months to restore. Flooding evacuation could involve 1.5 million residents in the inland region and delta counties.

Business interruption costs reach $325 billion in addition to the $400 billion property repair costs, meaning that an ARkStorm could cost on the order of $725 billion, which is nearly 3 times the loss deemed to be realistic by the ShakeOut authors for a severe southern California earthquake, an event with roughly the same annual occurrence probability.

Overview of the ARkStorm Scenario    USGS

In the News ...

Noah's Ark has nothing on this Calif. forecast   MSNBC - January 16, 2011

One of the biggest fears for most Californians is "the big one." Many of us expect to one day experience a major earthquake that will cause major calamity. We have a state agency filled with brilliant men and women who track even the smallest of quakes hoping to find a way to predict "the big one." So you might be surprised that a group of 117 scientists who work for the USGS aren't talking about earthquakes and instead are warning us of something that could be even more destructive.

The USGS unveiled Friday a new study of what they call an "Arkstorm Scenario." It's a mega-storm that would measure rain in feet instead of inches. Playing off the Biblical story of Noah's ark, scientists say an Arkstorm is an every-other century occurrence. That might not be that far off once you look at the historical data.

For the novice, it is a weather system that plants itself out in the Pacific Ocean and the "storm door" never closes. You can see the weather map in the clip in this link. Arkstorm is a hypothetical scenario that describes a rainstorm that produces a 10-foot wall of water that could flood a swath of the state from the Yosemite Valley to the Pacific Ocean. A similar storm hit back in 1861 and left the central valley of California impassable.

Scientists didn't put a number in lives lost, but said it would leave in its wake destruction in the $300 billion range. The scenario combines prehistoric geologic flood history in California with modern flood mapping and climate-change projections to produce a hypothetical yet plausible scenario. The purpose is to prepare state and federal officials to be ready to mobilize an emergency response.

Chief Arkstorm scientist Lucy Jones said their models show one in four homes would experience flood damage. "We think this event happens once every 100 or 200 years or so, which puts it in the same category as our big San Andreas earthquakes. The Arkstorm is essentially two historic storms (January 1969 and February 1986) put back to back in a scientifically plausible way. The model is not an extremely extreme event," Jones said.

Unlike "the big one," a storm of this magnitude would take days if not weeks to become a reality. It's something meteorologists will have plenty to say about ahead of time.