La Niña is back. What does this mean for a parched southern California? | MCU Times

La Niña is back. What does this mean for a parched southern California?

NASA’s Jason-3 satellite shows anomalously cold water in the equatorial Pacific Ocean. (NASA’s Jet Propulsion Laboratory and Los Angeles Times)

La Niña is back for an encore – but few Californians are likely to welcome this cool diva.

As La Niña typically results in a drier winter than the winter in drought-stricken Southern California, this is not exactly welcome news. The condition, which affects the weather throughout the United States, has evolved since the summer and has already played a role in an above-normal Atlantic hurricane season this year.

La Niña is essentially the opposite of her hot and wet counterpart, El Niño, and is characterized by below-average sea temperatures in the central and east-central equatorial Pacific. Predictors predict that this La Niña will be moderately strong and give it an 87% chance of persisting from December to February, according to the National Oceanic and Atmospheric Administration’s Climate Prediction Center.

This is the second winter in a row that this phenomenon is developing.

A map showing what a La Ni ñ winter typically means for North America.

La Niña winters are typically drier than average in Southern California and southwest. (Paul Duginski / Los Angeles Times)

What is La Niña?

In addition to below-average sea surface temperatures in the tropical Pacific, easterly winds strengthen over this region, and precipitation usually falls over the central and eastern tropical Pacific and rises over the western Pacific, Indonesia, and the Philippines.

La Niñas usually weaken winds in the Caribbean and the tropical Atlantic, contributing to increased hurricane activity in the Atlantic area.

What does this mean for Southern California?

There are several global climate factors involved in forecasting precipitation, but La Niñas is typically associated with colder, more stormy-than-average conditions and increased precipitation in the northern United States and warmer, drier and less stormy conditions in the southern parts of the country.

The latest US drought monitoring, released on October 14th.

The latest U.S. drought surveillance data released Thursday shows California and the West plagued by severe drought. (Paul Duginski / Los Angeles Times)

California and large parts of the West remain gripped by extreme or extraordinary droughts, according to the latest U.S. drought monitoring data. The region needs rainfall to recharge soil moisture and increase groundwater levels, streams and reservoir levels, according to drought monitoring researchers.

This is especially true after a summer characterized at extreme heat California’s hottest summer ever recorded, actually.

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

Are La Niña winters always dry?

The short answer is, not necessarily.

But Bill Patzert, a retired climate scientist at NASA’s Jet Propulsion Laboratory who has studied the El Niño-Southern Oscillation (ENSO) for four decades, says the tire is likely to be stacked for another dry year.

The ENSO climate phenomenon has three phases: El Niño, a warming of the sea surface; its opposite, La Niña, which is a cooling of the sea surface; and a neutral phase in between. These changes in sea temperature are associated with changes in the atmosphere and winds.

Patzert uses annual rainfall figures (July to June) in downtown Los Angeles to represent Southern California, as the numbers in the center go back the farthest. El Niño and La Niña were not well documented until 1950, so he looked at the 72 rainy years through 2021. So it’s 1949-50 through 2020-21. (Precipitation year refers to the year in which it ended.)

During this time there were 25 La Niñas and 26 El Niños – so they occurred with approximately equal frequency.

The average rainfall for the La Niña years is 11.64 inches. The long-term average going back to 1878 in downtown LA is just shy of 15 inches. Last winter, during a moderate La Niña, the center got only 5.82 inches.

In 10 of the 25 La Niña years, downtown received less than 10 inches, so some of LA’s driest years come during La Niñas. In just four La Niña years, downtown LA has received above-average rainfall. So it’s rare, but it can happen. The wettest La Niña year was 2011, when downtown scored 20.20 inches of rain. In 2017, 19 centimeters of rain fell in the center, and it was during a weak La Niña. In 2016, it dropped only 9.6 inches and it was below a strong El Niño.

Recurrence of La Niñas is not uncommon and occurred most recently in the years 1973-74-75, 1998-99-200 and in 2007-08-09. Repeated La Niñas often follow El Niños.

So El Niños and La Niñas can be pretty unpredictable, says Patzert, “But the statistics favor drier La Niñas and wetter El Niños, which is not good news for water managers, farmers and firefighters.”

How do researchers study La Niñas?

Researchers at JPL in La Cañada Flintridge are studying the ENSO phenomenon with satellite technology that records the height of water in the Pacific Ocean.

As water expands when it is warmer, the sea level is higher. Where the water is colder, it contracts and the surface is lower. (Satellite imagery shows higher than normal heights in yellow and red, while lower altitudes are shown in blue and purple. Green indicates what is close to normal.)

Currently, the cooler La Niña water along the equator measures between 3 and 6 inches lower than normal.

So as the record shows, there are no guarantees, but “the conditions are ripe for a stormy, wet winter in the northwestern Pacific and a dry, relatively rain-free winter in southern California, the southwestern and southern layers of the United States,” he says. Patzert.

ENSO is still not fully understood and many other factors play a role in the global climate, but the Pacific Ocean is the 800 pound gorilla of climate factors. As Patzert likes to say, “When the Pacific speaks, we should all listen.”

This story originally appeared in Los Angeles Times.

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