It's like a fire hose spewing water non-stop. A new understanding of atmospheric rivers, which are high powered storms that pound an area for days or weeks with rain, shows California could potentially suffer $1 trillion in damage statewide from subsequent floods.
The U.S. Geological Survey dubbed that catastrophic storm "The Other Big One."
The research team found that such a massive storm could cause hundreds of landslides, flooding stretching 300 miles long in the Central Valley and serious damage in the state's major population centers.
"The loss numbers are potentially four to five times more than a large earthquake on the San Andreas Fault. Hence, our concern," said USGS director Marcia McNutt.
Though it wasn't the one, Southern California got a taste last month of an atmospheric river, known as an ARkStorm, dropping 17 inches of rain in one part of Los Angeles County in three days.
The USGS study looked at a worst-case storm: A torrent of tropical rain for nine days straight.
"When you get too much water, it overwhelms our storage system, and it has to go somewhere else. And that's where it can lead to catastrophe," said USGS chief scientist Lucy Jones.
Other megastorms in California include the one in late December and early January of 1861 and 1862, when Governor-elect Leland Stanford famously took a rowboat to his inauguration because it rained for 45 days. The USGS study notes such ARkStorms are rare.
"We're saying about every one to two centuries," said Jones.
Nonetheless, scientists urge communities and Californians to prepare. Only some levees are built for a 200-year storm.
"If we have better plan...it's going to save lives and properties," said Mike Dayton of the California Emergency Management Agency.
Scientists would like to next develop a storm-rating scale that's similar to the one used for hurricanes. That way, Californians can prepare based on the predicted severity.
The Associated Press contributed to this report.