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Dry Cycle May Spin On for Years

Weather: Region's drought could be auguring a longer trend, scientists warn.

June 30, 2002|ERIC MALNIC | TIMES STAFF WRITER

If it doesn't rain tonight, and it almost certainly won't, Los Angeles will have just completed its driest year in history.

And at least one expert says that this could be only the beginning, that Southern California and the rest of the Southwest may be experiencing the onset of dry weather that could last a decade or more.

"I don't think any El Nino's going to come riding in on a white horse and drop a lot of rain that'll rescue us from this drought," said Bill Patzert, an oceanographic meteorologist from the Jet Propulsion Laboratory in Pasadena. "It looks like we're in for a long, dry spell."

Rainfall at the Civic Center since July 1, 2001, has been a scant 4.42 inches, less than a third of normal and the least that has fallen on Los Angeles since they started keeping records in 1877.

But is this a drought? That depends on your point of view.

If you're a firefighter, it's a drought, all right. Wildfires already are crackling throughout Southern California, Arizona, New Mexico and southern Colorado, fueled by brush and trees desiccated by a four-year stretch of dry weather. This year's is one of the earliest fire seasons ever, and it promises to be one of the longest and most devastating.

"I've been in this business 28 years, and I've never seen it so bad," said Donald R. Feser, a U.S. Forest Service fire chief in the Angeles National Forest.

Ranchers and farmers dependent on timely rains for livestock feed and grain crops call it a drought, too.

"All the range-land guys are hurting," said Rob Frost, a cattle rancher in the hills north of Santa Paula. "It probably will force some people out of business."

But for typical urban residents of the Los Angeles Basin, it may not seem like a drought at all.

Meteorologists say the lack of rain we're experiencing now is due to a shift in the high-altitude jet stream winds that propel most storm systems from west to east in the northern hemisphere.

Southern California usually gets most of its rain between September and March, when the jet stream tends to drift far enough south to drive these storms into the coastal mountains that stretch from Point Conception to the Mexican border, dropping rain in the valleys and snow at higher elevations.

This year, according to Tim McClung, a National Weather Service meteorologist, a persistent ridge of high pressure stalled over Northern California and the Great Basin, deflecting the jet stream--and the storms that ride it--farther north than usual.

The result: Rainfall figures shrink the farther south you go. San Francisco received about the normal amount of rain; San Luis Obispo got 67%; Santa Barbara, 50%; Los Angeles, 29%; and some areas near the Salton Sea, about 4%.

By itself, this year's drought is troubling enough. But if Patzert's theory is right--and Kelly Redmond, a research meteorologist at the Western Regional Climate Center in Reno, says it could be--the shortfalls are part of a prolonged dry cycle that could be cause for major concern, especially for those firefighters and dry-land farmers.

Studying records that stretch back more than a century, the two men have concluded that there are multiple cyclical phenomena in the Pacific Ocean--driven by forces not yet fully understood--that may have enormous influence over whether the weather is wet or dry in Southern California.

One phenomenon is the familiar El Nino-La Nina cycle, characterized by fluctuating surface ocean temperatures in the eastern equatorial Pacific.

During El Ninos, when these temperatures are relatively warm, the high-pressure ridges drift east, the jet stream drifts south and Southern California sometimes gets much heavier rain than usual. An example was the winter of 1997-98, when more than 31 inches of rain fell on Los Angeles.

During La Ninas, when the equatorial surface temperatures are relatively cool, the high-pressure ridges stall, the jet stream is deflected north and Southern California almost always gets less rain than usual.

El Ninos and La Ninas occur at irregular intervals and seldom last more than a year or two. After the drenching El Nino winter of 1997-98, the cycle reversed, and the next two seasons were both La Ninas, with below-normal totals of 9.12 and then 11.57 inches of rain in Los Angeles.

The 2000-2001 season, with 17.94 inches in Los Angeles, was somewhat above normal, but Patzert considers that a local anomaly since most other cities in Southern California were at or below normal.

And then came this year, the driest year ever. And it was neither El Nino nor La Nina.

"Clearly, there are other forces at work," Patzert said.

These other forces, he said, apparently include a much longer cyclical phenomenon, rooted in the surface water temperatures farther north of the equator, known as the Pacific Decadal Oscillation.

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