Evacuations as storms inundate California

The latest Pacific storm has unleashed torrential downpours and damaging winds in California, knocking out power and turning city streets into rivers as mudslides cut off highways and entire communities faced evacuation orders.

More than 33 million Californians were threatened by severe weather throughout Tuesday as "heavy to excessive" rainfall was expected across the state, especially in southern California, as winds gusts were clocked at more than 64km/h in many places, the National Weather Service said.

The high winds wreaked havoc on the power grid, knocking out electricity to 180,000 homes and businesses as of midday.

"This storm was different from the standpoint that it was here much longer. It was more intense because of the prior storm, the ground was much more saturated, which led to a lot more flooding and a lot more rescues because of the ground saturation," said Barry Parker, division chief of the Ventura County Fire Department.

Experts say the growing frequency and intensity of such storms, interspersed with extreme heat and dry spells, are symptoms of climate change.

Though the rain and snow will help replenish reservoirs and aquifers, a mere two weeks of precipitation will not solve two decades of drought. Meanwhile, terrain denuded by past wildfires has created an increased risk of flash floods and mudslides.

The torrential rains, along with heavy snow in mountain areas, follow yet another "atmospheric river" of dense moisture funnelled into California from the tropical Pacific, powered by sprawling low-pressure systems churning offshore.

Much of the damage has been concentrated around the city of Santa Barbara, northwest of Los Angeles.

Several remote spots have reported more than 30cm of rain including the San Marcos Pass in the Santa Ynez Mountains above Santa Barbara, where more than 40cm have fallen.

On Monday, officials ordered the evacuation of some 25,000 people, including the entire affluent enclave of Montecito near Santa Barbara, due to heightened flood and mudslide risks. The 4000 people of Planada, a community in Central California, started their Tuesday morning with an order to evacuate their homes by the county sheriff's office.

The Montecito evacuation zone was among 17 California regions where authorities worry the ongoing torrential downpours could unleash lethal cascades of mud, boulders and other debris in the hillsides.

At least a dozen fatalities have been attributed to several back-to-back storms that have lashed California since December 26.