Sunday, February 25, 2024

La Niña on the horizon? California’s wild weather year could get even weirder

Storm-battered California is still grappling with a wet El Niño winter, but in an unexpected twist, La Niña could be on its heels.

The El Niño-La Niña Southern Oscillation, or ENSO, is a climate pattern in the tropical Pacific that can influence weather patterns around the world and throughout the Golden State, although its results are never guaranteed.

Typically, El Niño is associated with warm, humid winters in Southern California, while La Niña is associated with cooler, drier conditions.

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So far this year, El Niño has kept that promise. The trend has intensified in recent months, becoming what is now considered the fifth strongest El Niño on record, according to an advisory released this week by the National Oceanic and Atmospheric Administration.

Since December, California has been hit by intense atmospheric rivers, including three storms that brought record rainfall to Oxnard, San Diego and Los Angeles. The latest storm killed at least nine people and triggered landslides, debris flows and two tornadoes.

But California’s severe weather may not be over yet, as there is now a 55% chance that La Niña will develop between June and August, the advisory states. There is a 77% chance this will develop between September and November.

An aerial view of a Beverly Crest home that was pushed off its foundation by a mudslide.

A Beverly Crest home that was pushed off its foundation by a mudslide as an atmospheric river unleashed heavy rains in Southern California this week.

(Allen J. Schaben/Los Angeles Times)

“We’re looking at a lot of state-of-the-art climate models, and there’s broad consensus among those models that we could potentially move into a La Niña,” said Michelle L’Heureux, a climate scientist at Climate Change. NOAA. Prediction Center. “Overall, that’s why we issued this watch.”

La Niña tends to favor the opposite phenomenon of El Niño, L’Heureux said. During La Niña, the central and eastern Pacific Ocean cools and the jet stream – the river of air that moves storms eastward across the globe – shifts northward. The effect essentially creates a large ridge in the North Pacific Ocean, which “can help dry things out across the entire southern part of the United States, including California,” she said.

L’Heureux cautioned that it’s still very early in the year to make predictions about how next winter might play out in California. ENSO is more like a “big nudge” that encourages weather systems to reproduce along a certain preferred trajectory, as opposed to a guaranteed outcome.

“It’s still not a breeze,” she said of La Niña. “There is still a one in four chance that this will not happen, and it will be important to see this progress to be able to say something about the impacts. Because once it appears, then we can be a little more confident about certain impacts.

A rare episode of La Niña over three years The 2020 to 2023 period was a notable factor in California’s most recent drought, which led to unprecedented water restrictions, shrinking groundwater supplies, and record levels on the Colorado River.

If the latest forecasts are confirmed, the West Coast could once again experience a rapid shift from precipitation to drought – a phenomenon sometimes called “weather whiplash” that is becoming increasingly common in a warming world.

Indeed, El Niño and La Niña do not act alone. Climate change is also exerting a greater influence on conditions in California and the United States, and there is a “constant interaction” between ENSO and global warming, L’Heureux said.

“There will always be a boost from El Niño and La Niña, but there will also be a boost from climate change,” she said.

Chain installer Bill Siples at work along State Highway 330 en route to Big Bear

Bill Siples installs chains on the tires of a motorist heading toward Big Bear on State Highway 330 as snow fell in the area Tuesday.

(Robert Gauthier/Los Angeles Times)

That could result in more intense rainfall during El Niño years, she said — much like the conditions experienced in Los Angeles this week. On the La Niña side, that could mean more evaporation, more heat, and more extreme drought due to warmer conditions.

Additionally, there are other climate patterns that can influence California’s weather that are not predictable this early in the year, such as the Madden-Julian Oscillation, a rapid phenomenon in the tropical Pacific central which develops on a sub-seasonal time scale. . Random weather events are also not predictable that far away.

What all this means for California’s water supply remains to be seen.

As of this week, recent storms have filled the state’s largest reservoirs to 118% of their historical average. Statewide precipitation is 102% of average for this date, with more than 13 inches falling since the water year began Oct. 1, according to state data.

But most of the moisture fell in Southern California, and mostly as rain, leading some California Department of Water Resources officials to worry about a “snow drought.” . The slow, steady melting of the Sierra Nevada snowpack each spring and summer has long been a key component of the state’s water supply.

Last year, the Sierra was hit by intense cold storms that produced a near-record snowpack — 237 percent of normal on April 1, when it typically reaches its peak.

The latest round of storms provided a boost, increasing the snowpack to 76% of average for the date, up from 50% on January 31.

However, the Sierra snowpack is only halfway to its April 1 peak, “so if we see a prolonged dry spell, it is still possible to end the season with a snowpack below the average,” said Michael Anderson, state climatologist with DWR.

“As climate drivers like El Niño or La Niña alter large-scale weather patterns that impact the Northern Hemisphere, each year California’s water supply and flood or drought risks depend of the timing, rate and magnitude of atmospheric river storms,” Anderson said. . “When we miss these storms and we have warmer, drier winter days due to climate change, we start to slide into drought. If storms are too big, happen too quickly or persist, floods occur.”

DWR is working with federal, state and local partners to improve its seasonal forecasting capabilities, Anderson said. But it is also important to continue investing in other water management strategies, such as rainwater capture, groundwater recharge and recycled water, to ensure reliable water supplies.

“It is our responsibility as water managers to capture and store as much water as possible during wet periods like we are experiencing now, because we never know when drought conditions will return,” he said. he declared.

The forecast for the rest of the winter remains somewhat ambiguous. Above average temperatures are favored across the state through April, while above average precipitation is only favored in Southern California.

Additionally, the strong El Niño appears to be past its peak, L’Heureux said.

She added that it is not uncommon for a strong El Niño to give way to a La Niña – which happens in about 60% of historical cases.

Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, similarly said it’s not unusual to move from one side of ENSO to the other.

“However,” he said, “the predictability of standard time this early in the year is not very good, and so I would be wary of any forecast of La Niña until June/ July or so.”

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