El Niño is already pushing seawater into California's coastal communities, with cities from San Diego to the Bay Area dealing with intermittent flooding in recent weeks. Climate scientists warn this is only a preview of the winter ahead.
The flooding comes from a warming ocean. El Niño heats the Pacific and sends massive underwater waves toward the state, and as that water warms it expands, lifting sea levels along hundreds of miles of shoreline.
The larger danger is a pile-up of forces. If elevated seas line up with the year's highest tides, known as king tides, along with big waves and storms, several feet of water could hit the coast at the same time, a scenario scientists say could very well happen.
Those king tides are expected the weeks of Thanksgiving and Christmas, and they will run even higher than usual this year.
Rain poses a separate threat. More storms could bring additional flooding, landslides and rain instead of snow in the Sierra Nevada, though no extreme rain events have struck so far this year.
Cities shore up defenses
In Long Beach, boardwalks and homes were damaged last month. The city is reinforcing beaches with sand, strengthening a wall that separates its boardwalk from the ocean and giving sandbags to residents.
Joshua Hickman, the city's director of public works, described the effort as a lot of work against a lot of need. It is unclear to him whether the measures will be enough.
I'd be lying if I didn't say it keeps me up at night.
Joshua Hickman, director of Public Works, City of Long Beach
Farther north, towns all the way to the Oregon border are preparing for flooding and erosion. In Pacifica, a hilly city south of San Francisco where homes and businesses are built right up to the shoreline, the pier split in two during high surf in June.
Mayor Christine Bowles said the city is working to stabilize the pier so it is not lost this winter, among other flood preparations. She also urged residents to pitch in, such as by clearing leaves from nearby drains, rather than expecting the government to do everything.
Pacifica has fought severe coastal erosion for decades and has seen homes destroyed. During one past El Niño winter, about 90 feet of its coast disappeared.
A preview of the future
Some of the flooding threats tied to El Niño are predicted to become everyday problems in the coming decades as human-caused climate change raises sea levels. Coastal cities are developing long-term responses that range from larger sea walls to possibly retreating from the water's edge.
