(CNN) — Thousands of Californians remained under evacuation orders as heavy rainfall continued in parts of the state, threatening more flooding as part of a series of storms that have left at least 17 dead in recent weeks.

Thunderstorms were drenching northern California Tuesday afternoon with more rain expected Wednesday and Thursday. Across the state, more than 20 million people are under flood alerts as the risk of mudslides also spreads to the Los Angeles and San Diego areas.

"Scattered to widespread instances of flash flooding will be possible, especially near steep terrain and burn scars," the Weather Prediction Center said Tuesday afternoon.

Roughly 34,000 remained under evacuation orders statewide, California Gov. Gavin Newsom said in a Tuesday afternoon news conference.

The rain is part of a wave of atmospheric rivers — long, narrow regions in the atmosphere that can transport moisture thousands of miles — that have thrashed the West Coast in the last several weeks. The storms have led to dangerous flooding and mudslides and prompted evacuations across the state, with much of California getting rainfall totals that are 400 percent to 600 percent above average in that time.

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The rain is largely over for southern California until the end of the week, but California is not out of the woods: Four more atmospheric river events are expected in the next 10 days. Northern California's severe weather Wednesday and Thursday will be followed by a weekend storm, another weather event early next week and another just days after.

From north to south in the Golden State this week, flooding, mudslides or threats thereof have led to evacuations, road closures and desperate rescues. On Monday, trees crashed down, homes lost power and major roadways were turned into rivers or otherwise closed as storms unleashed powerful winds and heavy downpours.

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In Santa Cruz County just southwest of San Jose, Rachel Oliveria stayed home Monday as water from a nearby river rose and flooded her residence.

"Within a matter of minutes, it was from across the street all the way into our yard, and it went really fast," Oliveira said.

A wrap of recent developments:

• Two motorists killed: In interior California's San Joaquin Valley, a tree fell on a pickup truck on State Route 99 in Visalia early Tuesday, killing the driver and leading to the death of a motorcyclist who crashed into the tree, the California Highway Patrol said.

• Child missing: A 5-year-old boy was swept away by floodwaters Monday morning near the Salinas River in San Miguel, about a 215-mile drive northwest of Los Angeles, authorities said. An hours-long search for the child resumed Tuesday morning after a suspension for poor weather conditions Monday afternoon.

• Evacuations: Areas of the Salinas River were under evacuation orders Tuesday afternoon due to flooding, the Monterey County Sheriff's Office said on Twitter.

• Power outages: Storms have downed utility lines, contributing to power outages. More than 100,000 homes, businesses and other utility customers were without electricity service in California as of roughly 5:30 p.m. local time, according to PowerOutage.us.

President Joe Biden on Monday approved a measure to support California's efforts to respond to the storms that for weeks have whacked the state like cascading dominoes.

Deadly climate disaster for unhoused people

At least two of the people killed in California's storms were people experiencing homelessness.

Rebekah Rohde, 40, and Steven Sorensen, 61, were both found "with trees on top of their tents" over the weekend, according to a news release from the Sacramento County Coroner. Both were unhoused, according to the release.

In Southern California, just northwest of Los Angeles, at least 18 people were rescued Monday by the Ventura County Fire Department, including multiple people who were stranded on an island in the Ventura River, fire officials said. Many of the people who were rescued from the river were unhoused, the fire department said.

Unhoused people face the highest risks during severe weather events, the National Alliance to End Homelessness told CNN, adding that local authorities working to keep those individuals safe should lower any barriers that prevent people from going to shelters.

Those barriers can include shelter policies on whether partners and pets are allowed, how many bags and personal belongings an individual is allowed to bring, and how long someone has lived in the area, said Alex Visotzky, Senior California Policy Fellow at the alliance.

"If you're choosing between letting people drown because they're on a riverbed than letting them in (the shelter) because they have more than one or two bags of belongings, that's a problem," Visotzky said.

And the risks continue long after the storms for these communities, as many individuals may not have dry clothes and a warm place to go for days following the severe weather event and can end up getting sick, said Bob Erlenbusch, the executive director of the Sacramento Regional Coalition to End Homelessness.

'One of the worst storms' in a decade

Meanwhile, evacuation orders were lifted for the oceanside town of Montecito and nearby areas of Santa Barbara County, and residents were cleared to return to their homes, Santa Barbara County Sheriff Bill Brown announced Tuesday afternoon.

Montecito — located between the Santa Ynez Mountains and the Pacific Ocean in Southern California's Santa Barbara County — got Monday's evacuation orders on the five-year anniversary of a 2018 mudslide that killed 23 people as mud and boulders the size of houses plowed down hillsides, splintering more than 100 homes and rupturing a gas main, according to the state's Office of Emergency Services.

This week, the county was deluged with water, saw floods, mudslides, road closures, and multiple rescues, county officials said.

Crews in Santa Barbara County responded to more than 200 incident calls due to the heavy rains, Captain Scott Safechuck, spokesperson for a Santa Barbara County Incident Management Team, had said earlier.

Around 10 to 15 homes were damaged due to flooding in the county on Monday, according to Santa Barbara County Fire, which released images showing a flooded neighborhood and a sinkhole that developed.

In Pasadena, a Servpro cleanup and restoration vehicle was hit by a falling tree Tuesday, but was unoccupied and no injuries were reported, according to Lisa Derderian, a spokesperson for the city. Derderian said it was likely that high winds and the over-saturated soil in the area caused the larger tree to topple.

"This has been one of the worst storms we've seen in the past 10 years," Derderian told CNN.

Servpro declined to comment on the incident, but assured CNN their employees are unharmed.

To the north, on the central coast, Santa Cruz County saw widespread damage Monday, according to images from Cal Fire. The San Lorenzo River swelled 14 feet in just over four hours Monday morning as heavy rain pounded the region, putting the river in a major flood stage.

Fast-moving water in Santa Cruz knocked out a bridge and flooded state parks, video showed.

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