Jun 12 2015

El Niño continues to build, raising chances of wet winter

Gino Celli inspects wheat nearing harvest in May on his farm near Stockton. Moving to meet voluntary water conservation targets, dozens of farmers in the Sacramento-San Joaquin River Delta submitted plans to the state saying they intend to plant less thirsty crops and leave some fields unplanted amid the relentless California drought, officials said. AP Photo — Rich Pedroncelli

 

In a promising trend that increases the likelihood of steady storms this winter that could ease California’s historic drought, federal scientists on Thursday reported that El Niño conditions in the Pacific Ocean are continuing to grow stronger.

The probability of an El Niño — defined as warmer water at the equator and shifting winds that can bring major weather changes — being present through the end of 2015 is now 85 percent, up from 80 percent last month, and 50 percent three months ago, according to the National Oceanic and Atmospheric Administration.

“The big takeaway is that obviously El Niño has strengthened,” said Mike Halpert, deputy director for NOAA’s climate prediction center in College Park, Maryland.

“We are more confident that it is going to last through the rest of the year, and at this point, we’re slightly favoring a strong event.”

Most important: Trade winds are shifting in ways consistent with prior big El Niños, and sea surface temperatures in the Pacific Ocean near the equator are now 2 degrees Fahrenheit warmer than average in all five zones that El Niño researchers study, a trend not seen since 1997 when a California was hit was drenching rains and floods the following winter.

To be sure, there are still six months before California’s winter rainy season. Many of those are expected to be brutally dry and hot summer months, with high fire risk. And scientists say promising El Niños have fizzled out in the past, most recently last year.

“El Niño is a bad boy, and sometimes he disappoints. He could abandon us at the altar. It’s not a sure thing at this point,” said Bill Patzert, a research scientist and oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena.

“But it’s probably a good idea to clean out the flood control channels in preparation for January.”

 

Water Warning

California water officials have worried that news of a building El Niño could cause state residents to ease off water conservation. That could cause emergency shortages next year if El Niño doesn’t deliver a very wet winter, they note, given the state’s low reservoirs, depleted groundwater, rainfall deficits and non-existent snowpack after four years of historic drought.

“Very few of us would empty our bank accounts today on the hopes of hitting the lottery next winter,” said Doug Carlson, a spokesman for the state Department of Water Resources. “And in the same vein, we can hope for rain, but we have to continue to conserve today.”

In recent months, unusual weather patterns have been linked by some researchers to the growing El Niño in the Pacific.

Two weeks ago, torrential storms battered Texas, killing more than 20 people, sending rivers raging over their banks and trapping thousands of people in flooded cars around Dallas and Houston. On May 25, Houston received a stunning 11 inches of rain in one night. By comparison, San Jose has received 13 inches in the past eight months, and Los Angeles 8 inches over the same time period.

That series of storms, which largely ended an ongoing drought in Texas, was caused when the sub-tropical jet stream moved north from Central America, a condition consistent with strong El Niño conditions, experts say.

“You are seeing flooding in Northern Mexico, which is normally very dry, and extreme drought in Nicaragua, which is normally very wet, which are characteristics of El Niño,” Patzert said.

Researchers stress that not all El Niño years bring big rains to California.

 

Ocean Water

Generally speaking, the warmer the ocean waters are during El Niño years, the greater the likelihood of heavy winter rains in California. During mild El Niño years, when the ocean water is only slightly warmer than historic averages, there are just as many dry winters in California as soaking ones.

Since 1951, there have been six winters with strong El Niño conditions. In four of them, rainfall from the Bay Area to Bakersfield was at least 140 percent of the historic average, according to studies by Saratoga meteorologist Jan Null.

But in the 16 winters since 1951 when there was a weak or moderate El Niño, California experienced below-normal rainfall in six of them, average rainfall in five and above-normal rainfall in the other five.

The term El Niño — or “little boy” in Spanish — was originally used by fishermen off Ecuador and Peru to refer to “the Christ child” because the warming ocean conditions appeared around Christmas every three to eight years.

Typically, El Niños begin when trade winds that normally blow westward, toward Asia, weaken, and then blow the other way. That allows warm ocean water near the equator to spread east, toward South America. Rainfall follows the warm water, which can mean wet winters for California, Peru and other areas, and droughts in Australia.

The opposite, or cooling ocean water, is a “La Niña.”

 

Projections

With each month that draws closer to California’s winter rainy season, forecasts become more reliable.

Currently, an ocean area that scientists call the “3.4 region” along the equator near South America that is considered a key indictor of El Niño trends is 1.2 degrees Celsius, or 2.1 degrees Fahrenheit, above the historic average. That departure from normal is twice what it was a year ago.

And the trend is expected to keep growing.

Supercomputers at NOAA, NASA and other world-leading scientific institutions are projecting the temperatures in that ocean region to hit 1.6 degrees Celsius, or nearly 3 degrees Fahrenheit, on average by September. The last time temperatures there reached that level in a September was in 1997, when they hit 2.3 degrees Celsius, or 4.1 degrees Fahrenheit, above average.

What followed was among the wettest winters in California history, similar to another strong El Niño year, 1982-83, with California receiving twice as much rain as normal. In February 1998, four weeks of storms and powerful winds led to mud slides and widespread flooding that killed 17 people and caused 35 California counties to be declared federal disaster areas from the Napa Valley to the Southern California coast.

“Be careful what you wish for,” said Patzert.


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