US president will visit hard-hit areas of California where flooding, intense waves and mudslides forced evacuations.

US President Joe Biden has arrived in California to assess the damage from a series of devastating storms that slammed the western United States, damaging homes and forcing residents to flee mudslides and rising floodwaters.

Biden touched down at Moffett Federal Airfield on Thursday for an aerial tour of Santa Clara and Santa Cruz counties, which were among the areas hardest hit by what is expected to be the state’s first, billion-dollar natural disaster of the year.

The seaside town of Capitola saw its historic wooden wharf ripped in two, while local beaches are still littered with debris after flooding from three straight weeks of severe weather.

Biden, who issued an emergency declaration for California last weekend due to the storms, is scheduled to meet with first responders and elected officials on his visit to the state, including Governor Gavin Newsom, a fellow Democrat.

Nine consecutive “atmospheric rivers” – intense, narrow bands of concentrated moisture capable of producing torrential rain and powerful gusts – battered California since late December, with a tenth, smaller storm system moving ashore on Wednesday.

“When I talked to people on the ground, what they told me is that these storms are coming with hurricane-strength winds,” Deanne Criswell, an administrator with the Federal Emergency Management Agency (FEMA), told reporters as she travelled with the president on Thursday.

“They’re also making incredible storm-surge-like conditions with the surf. So they felt like it was being hit by hurricane after hurricane,” she said.

The storm systems dropped an estimated 121 trillion litres (32 trillion gallons) of precipitation on California, resulting in record rain in San Francisco and Los Angeles and heavy snow in the Sierra Nevada mountain range.

As of Wednesday, the California Department of Water Resources estimated that snowpack across the state has surged to 248 percent of its normal levels, with parts of the Sierras recording a 292 percent increase.

The storms have resulted in widespread devastation, with at least 20 people reported dead.

Criswell, the FEMA administrator, said some residents were asked to evacuate up to four times to flee deadly floods and mudslides.

The White House estimated that more than 500 personnel from FEMA and other federal agencies are on the ground in California to address the damage.

On Wednesday night, the Biden administration authorised additional disaster assistance, pledging that the federal government would cover 100 percent of the total eligible costs for debris removal and emergency protective measures for 60 days.

The administration late on Saturday had authorised a request from Newsom, the California governor, to approve an “expedited major disaster declaration” to allow for federal assistance in the area.

The California Governor’s Office of Emergency Services said such declarations are requested when damage is so severe “it is beyond the combined capabilities of state and local governments to respond”.

Meanwhile, a study issued on Thursday in the journal Nature Climate Change predicted that California and other states in the western US could see a 31 percent increase in precipitation from similar cold-season storms in the future if climate change goes unchecked.

One area of California, approximately 378km (235 miles) north of San Francisco, received 1,213mm (47.74 inches) of rain in the past three weeks alone.

“It could be even worse,” the study’s author, Ruby Leung, a climate scientist at the US Pacific Northwest National Lab, told The Associated Press news agency. “We need to start planning how would we be able to deal with this.”