“What this shows is that in addition to flood risks being amplified by sea level rise, it can also be amplified by the fact that waves are increasing,” said Patrick Barnard, a research geologist with the United States Geological Survey. “That’s a factor that we have to consider as well as we plan to create resilient communities in the face of rising — not just sea levels but also rising levels during storms.”

Ian Young, a professor of oceanography at the University of Melbourne, in Australia, said that Dr. Bromirski’s conclusions were consistent with previous research using satellite data from the 1980s to study wave heights, and helped to show that the changes had been occurring over a longer period. “There is clearly a long-term trend,” he said.

Those changes were apparent early this year, when one atmospheric river after another battered the West Coast. The severe weather left homes in Santa Cruz, Calif., damaged by flooding and wind. Several months later, a landslide caused homes in one of Los Angeles County’s most affluent neighborhoods to collapse into a canyon. And when it comes to the waves, a sudden deluge can overwhelm coastal areas, destroy infrastructure and contribute to erosion.

Even pro surfers worry: Bigger is not always better.

“If the waves are huge, but it’s stormy and windy with chop, surfers are not going to be able to surf those waves,” Tyler Fox, a big wave surfer in Santa Cruz, said of ocean conditions that can include many small waves that make the water’s surface rough.

Mr. Fox, 42, has been surfing for more than three decades, and said that there are some spots where, at high tide, it is no longer possible to enter the water. In other places, he said, sections of cliff have calved off into the water, creating new hazards. Violent storms can also hurl the debris from damaged trees, homes and other structures into the ocean, he said, “basically into my sanctuary, a place that I love.”

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