La Niña is back. What does that mean for dry Southern California?


Image from NASA's Jason-3 satellite showing cold water in the equatorial Pacific Ocean.

NASA’s Jason 3 satellites show unusually cold water in the equatorial Pacific Ocean. (NASA’s Jet Propulsion Laboratory and the Los Angeles Times)

La Niña is back in Angkor, but few Californians will admire this chilly diva.

This is not always welcome news, as the La Niña phenomenon usually results in a drier than average winter in drought-stricken Southern California. This condition, which affects the weather across the United States, has evolved since summer and is already participating in the more than usual Atlantic hurricane season this year.

La Niña is essentially the opposite of her warm and moist counterpart, El Nino, characterized by sub-average sea surface temperatures in the central and eastern central equatorial Pacific Oceans. According to the National Oceanic and Atmospheric Administration’s Climate Prediction Center, forecasters predict that the La Niña is moderately strong and has an 87% chance of lasting from December to February.

This phenomenon occurred in winter for the second consecutive year.

La Ni & # xf1; A map showing what winter usually means for North America.

Winters in La Niña are usually drier than the average in Southern California and Southwest. (Paul Duginsky / Los Angeles Times)

What is La Niña?

In addition to sub-average sea surface temperatures in the tropical Pacific, the region’s easterly winds intensify, with rainfall usually decreasing in the central and eastern parts of the tropical Pacific and increasing in the western Pacific, Indonesia, and the Philippines.

The La Niña phenomenon usually weakens wind shear in the Caribbean and tropical Atlantic Oceans and contributes to increased hurricane activity in the Atlantic Basin.

What does that mean for Southern California?

Although many global climatic factors are involved in predicting precipitation, La Niña is usually colder than average, more stormy, more precipitation, and warmer and drier in the south throughout the United States. , Related to less storm conditions. country’s.

The latest US drought monitor released on October 14th.

The latest US drought monitor data released Thursday shows that California and the West are suffering from severe droughts. (Paul Duginsky / Los Angeles Times)

Many in California and the West continue to suffer from extreme or exceptional droughts, according to the latest US drought monitor data. According to Drought Monitor scientists, precipitation is needed in the area to recharge soil moisture and raise groundwater levels, stream flows, and reservoir water levels.

This is especially summer Characterized In extreme heat — In fact, California’s hottest summer ever recorded.

Climate scientist Daniel Swain tweeted on Wednesday that the current drought in California is worse than the 2014-15 drought, making it the worst drought ever since the late 1800s.

Is the winter in La Niña always dry?

The simple answer is not always so.

But Bill Patzert, a retired climate scientist at NASA’s Jet Propulsion Laboratory, who has been studying El Nino Southern Oscillation (ENSO) for 40 years, says the decks are probably piled up to dry for another year. ..

The ENSO climate phenomenon has three phases: El Nino, warming sea level. On the contrary, La Niña is the cooling of the sea surface. And the neutral phase in the meantime. These changes in seawater temperature are linked to changes in the atmosphere and wind.

Patzert represents Southern California using the annual rainfall (July-June) in downtown Los Angeles. This is because the downtown numbers are the farthest. El Nino and La Niña were not well documented prior to 1950, so we looked at rainfall for the 72 years to 2021. That is, from 1949-50 to 2020-21. (The rainy year is the year when the rain ends.)

In the meantime, there were 25 La Niña and 26 El Nino, so they happened about the same frequency.

The average annual rainfall in La Niña is 11.64 inches. The long-term average dating back to 1878 in downtown Los Angeles is a 15-inch shy. Last winter, during a modest Lanina, downtown was only 5.82 inches.

In 10 of the 25 years of the La Niña phenomenon, downtown coverage was less than 10 inches. As a result, some of LA’s driest years are during the La Niña phenomenon. In just four years in La Niña, downtown Los Angeles recorded above-average rainfall. Therefore, it is rare, but it can occur. The rainiest year in La Niña was 2011, with 20.20 inches of rain in downtown. In 2017, 19-inch rain fell downtown. It was a time when the La Niña phenomenon was weak. In 2016, it fell only 9.6 inches, which was a time of strong El Nino.

The repetition of La Niñas is not uncommon, most recently in 1973-74-75, 1998-99-200 and 2007-08-09. Repeating La Niña often follows El Nino.

Therefore, El Nino and La Niña can be quite unpredictable. “But statistics favor drier La Niña and damp El Nino. This is not good news for water managers, farmers and firefighters.”

How do scientists study La Niña?

JPL scientists at La Cañada Flintridge are studying the ENSO phenomenon using satellite technology to detect water levels in the Pacific Ocean.

As the water expands as it gets warmer, the sea level rises. When the water is cold, it shrinks and the surface becomes low. (In satellite imagery, higher than normal heights are shown in yellow and red, lower heights are shown in blue and purple, and green is near normal.)

Currently, the colder La Niña water along the equator is 3 to 6 inches lower than normal.

Therefore, as the records show, there is no guarantee, but “stormy and rainy winter conditions in the Pacific Northwest and dry, relatively rainless winter conditions in Southern California, the Southwest, and the southern layers of the United States. Is ripe. ” Patzert says.

The Pacific Ocean is a 800-pound gorilla of climate factors, although ENSO is not yet fully understood and many other factors affect the Earth’s climate. As Patzert likes to say, “When the Pacific speaks, we should all listen.”

This story was originally Los Angeles Times..

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