Here’s how El Niño could devastate California — again

By Andrew Freedman, CNN

(CNN) — In February 1998, almost a year’s worth of rain fell in downtown Los Angeles, as a series of powerful Pacific storms rocked California amid a “Super” El Niño. Deadly landslides struck Southern and Central California, wiping out hillside homes, and powerful waves pounded the state’s shoreline. These waves destroyed a large section of the famous Santa Monica Pier and caused widespread coastal flooding in San Francisco Bay communities.

Many Californians who experienced that event still consider it to be the benchmark for how a Super El Niño can alter life in their state. Now, with another Super El Niño setting in — this time likely to be the strongest on record — many are calibrating their expectations based on what happened then.

However, El Niños of the past are not necessarily an accurate guide to El Niños of the future, experts say. The 2015-2016 Super El Niño, for example, didn’t drop near as much rain on California as its predecessor. And this current El Niño is especially a wildcard given the simultaneous influence of global warming due to climate pollution, which could worsen some of El Niño’s impacts.

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It is clear, though, that California is again likely to be an epicenter for this historically intense El Niño in the US. Strong El Niño events, such as the one revving up in the tropical Pacific, have rarely spared the Golden State from significant and damaging consequences.

This time, the state is likely to experience hazards ranging from widespread coastal flooding to heavy rain at lower elevations and mountain snows. Towering waves generated by intense Pacific storm systems, their heights amplified by El Niño, could erode parts of the fragile coastline and shut down crucial coastal transportation arteries.

California stands to experience its highest tide levels on record when this event peaks during the late fall through the winter. Extensive coastal flooding is almost guaranteed, scientists say.

These El Niño-related hazards are baked into the forecast regardless of where any intense Pacific storms eventually track, since El Niño increases coastal water levels on top of already rising sea levels from climate change.

This increase happens for two reasons — both tied to the fact that El Niño is characterized by warmer than average ocean temperatures in the equatorial tropical Pacific Ocean.

First, those El Niño-warmed ocean waters expand to take up more room. Second, the waves instrumental in forming El Niño in the Pacific take a turn to the north when they reach the South American coast.

Called “Kelvin waves”, these waves don’t crash and break. Instead, they’re massive, slow-moving and slosh up and down, like water in a bathtub. In the western Pacific, they’re the force that moves vast quantities of hot water eastward along the equator, helping to create El Niño. But once they hit land in South America, Kelvin waves can become coastally trapped, moving north and south, parallel to the coast — raising sea levels by six inches to one foot as they go.

Satellite imagery has already spied an area of rising seas expanding north from South and Central America to California’s Baja Peninsula, with a northward expansion expected from there.

To make matters worse, this year’s El Niño comes at the peak of an 18-year high-tide cycle — a natural, astronomical event that will make King Tides even higher than they otherwise would be, according to Patrick Barnard, research director at the Center for Coastal Climate Resilience at the University of California, Santa Cruz.

And then there’s just the regular kind of waves, formed by storms. Barnard said studies have shown that Pacific storms generate about 30% more wave energy during an El Niño year compared to a year without the climate cycle. Some past Super El Niño years, like the 2015-to-2016 event, showed even higher increases in wave energy of up to 50%, he said.

According to Barnard, the expected increase in coastal water levels during this El Niño — from six inches to a foot — would threaten an additional 170,000 people and an additional $60 billion in property, compared to a non-Super El Niño year.

Barnard and other experts emphasized the certainty of the coastal impacts, compared to the less predictable precipitation aspects of Super El Niño events in California.

“We do know we’re going to have these coastal hazards,” Barnard said.

Rain can be more fickle than waves

Less of a sure bet is where exactly the Pacific storm track will set up, since some El Niño events have hammered Northern California with heavy precipitation, while others have either fizzled on the rain front or taken aim at Southern California.

“Typically, we think of El Niño driving wetter than normal conditions for much of the American Southwest and drier than normal conditions for the Pacific Northwest, and that signal is pretty robust for the largest events,” said Dillon Amaya, a meteorologist at North Carolina State University. “But it’s not a perfect, one-to-one correlation,” he cautioned.

“The dice are definitely loaded in terms of rainfall. Where that happens is hard to predict,” Barnard said.

It’s less likely that heavy rains and mountain snows will be a no-show this winter, as studies have found that strong El Niños are correlated with heavier-than-average precipitation across the state. The El Niño-connected storms could combine with the higher-than-average storm-connected waves to manifest hazards such as flooding, mudslides and landslides.

Past Super El Niño events, such as the one from spring 1997 to spring 1998, have not been kind to California. In the San Francisco Bay area, more than 200% of average rainfall fell during the wet season from supercharged storms, and Central California overall also saw near record rain during that same Super El Niño. There were deaths caused by flooding and mudslides, as well as that coastal damage from higher water levels and wind-driven waves.

“That event really informs our expectations, both in the scientific community and in the public, for what any given El Niño might produce because of how impactful that particular event was,” Amaya said.

It is possible that the global warming that has taken place since the 1997-to-1998 event, or even since the 2015-to-2016 Super El Niño, may alter some of the typical outcomes. Some could be worse than before, while others may not show up at all.

Amaya said there is little doubt that the ongoing El Niño is headed for an extraordinary peak intensity, given how much heat lurks just beneath the surface of the tropical Pacific, destined to rise up over time.

“We’re definitely on a Super El Niño trajectory,” Amaya said. “I would be willing to bet my house on it; we’re going to get there.”

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