Scientists say a plausible California superstorm that could devastate the state would be fed by an "atmospheric river" moving water at the same rate as 50 Mississippi rivers discharging water into the Gulf of Mexico.
Scientists who study historic storms to understand the risks modern California faces discussed on Friday a developing scaling system to measure the intensity of an atmospheric river — a huge hose-like flow of Pacific Ocean moisture into the state.
A storm scenario released by the U.S. Geological Survey this week says such a storm has the potential to cause flood damage to a quarter of the houses in the state.
The report, based on computer models analyzing the impacts of two storms that soaked the state in 1969 and 1986, describes a storm lasting more than 40 days and dumping up to 10 feet of rain.
A team of 117 scientists, engineers, lifeline operators, emergency planners and insurance experts worked for two years on the project for the purpose of emergency planning. They named the weather event "ARkStorm," after an intense atmospheric river storm that would overwhelm the state's flood protection system, cause massive flooding, hundreds of landslides and serious damage in the state's major population centers.
"We create these scenarios to understand what are the implication of the types of very rare events that science tell us has to happen in our future," Lucy Jones, chief scientist of the USGS Multi-Hazards Demonstration Project, said following a symposium with the researchers at the University of California, Davis.
Jones said geological records show superstorms happened numerous times in the past, with the same frequency as a big earthquake striking the San Andreas Fault.
The "ARkStorm" project has resulted in the first statewide map detailing areas susceptible to landslides, a modeling system for analyzing severe storm impacts to coastal areas, and a scaling system to categorize the intensity of atmospheric rivers — the force behind most winter storms over California.
The scaling system is in the works, but so far scientists have estimated that the atmospheric river that fed a powerful storm over California last month moved water at 20 times the rate of water discharging from the Mississippi River into the Gulf.
The scale visualizes the amount and intensity of moisture rolling through the atmospheric river and helps scientists understand the severity of a storm, said Mark Jackson, meteorologist-in-charge of the National Weather Service in Oxnard.
He said historical records show California has had several storms in which 16 inches of rain fell in three days — the same amount left in the wake of hurricanes over Gulf Coast states.
"Our storms really are as bad as hurricanes in the amount of rain that they can bring," USGS Director Marcia McNutt said. "Without that type of labeling, we haven't recognized that our storms are that bad and we risk underestimating emergency response (to storms)."