Dry Cycle May Spin On for Years
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.
Patzert said that in the positive phase, these surface waters tend to cool in the north; in the negative phase, they tend to warm. He said these oscillations, which apparently affect the flow of ocean and wind currents, may influence weather in Los Angeles and the Southwest for periods that last as long as 20 years.
“In the 1950s and 1960s, rainfall was generally less than normal,” he said. “That was a negative phase. There was a positive phase in the ‘80s and ‘90s. But after the El Nino of ’97-'98, we went back into another negative phase, and I think we’re in that now. These negative phases, coupled with La Ninas, are the demon divas of drought.”
While the National Oceanic and Atmospheric Administration has predicted another moderate El Nino next winter, Patzert said, any tendency that might have to increase rainfall probably will be overridden by the negative oscillation.
“This negative oscillation could last another five or six years, maybe even longer,” Patzert said. “There might be a wet year here and there, but overall, it looks pretty dry.”
Redmond is more cautious.
“Are we getting back to a period, like the ‘50s and ‘60s, when it was generally drier than normal? That’s an open question,” Redmond said. The period during which detailed data have been collected--mostly since World War II--is still too short to extrapolate with great confidence. State water officials argue that Patzert’s theory is based largely on conjecture.
“There’s no hard evidence that permits you to forecast that far ahead,” said Jeanine Jones, an engineer with the state’s Department of Water Resources.
The Forest Service’s Feser isn’t looking beyond this year. He’s concerned with the here and now. He said he knew there was trouble as far back as Easter, when a small blaze started in Susana Canyon, in the Angeles National Forest.
“The humidity was low and the winds weren’t bad, but that fire spread rapidly over more than 100 acres,” he said. “When a fire burns that well on a day not conducive to extreme fire behavior, that’s a bad sign.”
Feser said the problem was an extraordinarily low level of moisture in the brush that burned.
Under formulas used by firefighting agencies, the weight of that moisture is compared with the weight of the plant’s dry, woody fibers. The ratio is expressed in percentages--100% would mean the moisture in a plant equaled the weight of the fibers. Because plants are like sponges, they can absorb more than their dry weight, so figures over 100% are possible.
“Normally, that brush would be at about 150% by now, but it’s already down to between 70% and 80%,” Feser said. “We consider 65% the critical level, and we’re almost there already. By the end of the summer, it’ll be down to 50%, low enough to kill the whole plant. At that level, brush burns like gasoline.”
Dave Franz, a spokesman for the California Farm Bureau Federation, a nonprofit lobbying group representing about 95,000 farmers in the state, said the lack of rain in Southern California has cut back natural forage about 95% in Ventura County, where Frost runs his cattle. Riverside County farmers dependent on rain for their grain crops are hard hit, Franz said.
But Franz said most of the farmers in California--by far the largest agricultural state in the nation, with revenues in 2000 of more than $35 billion--either are situated far enough north to have had ample rain or have plenty of irrigating water.
And in Los Angeles, suburban lawns are likely to remain green. Because of what well may be the largest and most sophisticated water catchment, storage and delivery systems on Earth, Southern Californians should have plenty of water to keep their crops green all summer long. Thanks to ample supplies transported hundreds of miles from wetter areas, the likelihood of water rationing in most of Southern California is virtually nil.
Jones of the water resources department said that 60% of Southern California’s water supply is from elsewhere, brought in by the State Water Project, the Los Angeles Aqueduct and aqueducts from the Colorado River. The other 40%, she said, comes mostly from groundwater basins in Southern California that remain in pretty good shape.
“Rainfall in the north is close to normal, so there’s plenty of water for the state Water Project,” she said. “The Owens Valley is drier than normal, but the L.A. Aqueduct (which draws its water from the Owens Valley) is a pretty small contributor. The Colorado Basin storage system is down to 70% of capacity, but it’s a huge system, capable of storing four times the average annual flow.”
Overall, Jones said, the water supply in Southern California looks adequate, except for a few mountain communities, like Idyllwild, that are dependent solely on rainfall for their water.
“There shouldn’t be any major problems,” she said.