What's Causing California's Drought?

First of three parts. Meteorologists know the conditions that are causing the California drought. But they don't know what's causing the conditions. And the historical record suggests that things could possibly get worse before they get better.


In what Californians like to think of as normal winters, southwest winds from the ocean deliver the lifeblood of the nation's most populous state - water.

The southwesterlies, arising in ocean storms north of Hawaii, sweep across the Pacific Ocean loading up moisture. When they bump into the towering Sierra Nevada, they drop rain on lower slopes and snow among the peaks.

But for unexplained reasons, the winds have failed California. Barring a near-miraculous turn-around in the next few weeks, this will be the fifth straight dry winter.

``What's hurting California is that they're not getting the Hawaiian connection,'' said Jim Wagner of the National Weather Service's climate-analysis center. ``There have been good storms north of Hawaii this winter, but they are weakened by the time they get to California.''

And that has really hurt in a state where nature, particularly in designing the southern part, seemed to have a desert in mind.

As California faces what may be the most economically devastating drought in its history, water deliveries to some farming areas have been suspended and water rationing imposed in selected

areas. Losses in agriculture alone this year because of land left unplanted for lack of water are estimated at $642 million. Thousands of farm workers could be laid off. Possible later costs to nonfarm industries could be even greater.

What's more, the drought does not show any sign of easing. With meteorologists puzzled as to underlying causes of the drought, efforts to combat it are pathetically puny, mostly attempts to wring a bit more snow out of clouds as they cross the mountains.

At least 15 agencies are seeding clouds, when the right kinds come by, trying to add a little snow above the reservoirs that collect the spring runoff and send water through giant aqueducts to Southern California.

``Most of the effort is in the high Sierra with the goal of augmenting snowfall by seeding storms that naturally would be rather inefficient,'' said Maurice Roos of the state's department of water resources. ``They may be increasing snowfall by several percent.''

The state's snowpack on Feb. 1 was 20 percent of normal. ``Pretty grim,'' Roos said.

As is the case in the Pacific Northwest, California counts heavily on winter snows to supply its thirsty farms, industries and cities. Three huge aqueducts convey water from usually water-rich areas to Southern California: The Colorado River Aqueduct crosses a desert from the Arizona border and pumps water over mountains to the city; the Los Angeles Aqueduct runs from the Owens Valley east of the Sierra Nevada; and the California Aqueduct collects water from the Sacramento River and tributaries.

The great aqueducts converge on the Los Angeles area, but this year they may not run full.

Water shortages - and surpluses - are nothing new in California. In fact, this drought would be even more severe except for an extremely wet late winter/early spring in 1986.

``We had a real flooding episode in central California in 1986,'' said Dan Cayan, climate researcher at the Scripps Institute of Oceanography in La Jolla.

``Water supplies were really stocked up. Were it not for that, our problems now, bad as they are, would be a lot worse.''

For water managers who depend on such occasional wet years to restock supplies, Joel Michaelsen of the University of California at Santa Barbara has some sobering information.

A study of tree rings, which are narrow during dry years and wide during wet ones, revealed a 40-year stretch without a wet year in Southern California during the early 1700s. Individual years weren't particularly dry, Michaelsen said, but there wasn't a single wet one over 40 years.

``If you're worried about filling up reservoirs, that kind of period would be very difficult to deal with,'' Michaelsen said.

But Michaelsen's trees also recorded some extremely wet periods in Southern California. He estimated precipitation in the 1560s was three to four times as wet as modern long-term normals.

So far as Michaelsen knows, no one has come up with a good explanation for what caused the droughts or wet periods of the past.

Luckily for Los Angeles, droughts usually don't hit the Upper Colorado Basin and the Sacramento Basin the same years. In the drought years of 1976-'77, the central and northern parts of the state suffered but the Colorado River helped Southern California avoid severe problems.

This time it's different. The drought is also affecting the watersheds that feed the Colorado River system.

David Meko, of the University of Arizona's tree-ring laboratory, is trying to find out how often that has happened in the past.

``The worst case for putting stress on water storage is when they coincide,'' Meko said. ``Luckily, there is little correlation in drought history (between the Upper Colorado and Northern California).

``But there have been some unusual cases of extended low flow in both systems, the most notable in the years 1579 through 1598.''

Those years, as recorded by tree rings, were the driest ever in the Colorado system and one of the four lowest on what hydrologists call the Four Rivers Index, a measure of reconstructed stream flow of the Sacramento, Feather, Yuba and American rivers.

The driest period ever on the Four Rivers Index was from 1918 through 1937. That drought was reflected in tree rings as far north as Washington state and in a decreased flow of the Columbia River, Meko said. But, luckily for Southern California, some of those years were really wet in the Colorado River system.

``In fact, 1905 through 1924 was the wettest period on the Upper Colorado in our tree-ring records, which go back to the year 1520,'' Meko said.

That same 20-year period, the wettest ever, was used as the basis for water allocation under the Colorado River Compact, a prank by nature that water managers have had ample opportunity to ponder ever since.

Climate cycles? Neither Michaelsen nor Meko has found any in their tree-ring studies.

The tree-ring record ``makes me shy away from saying the present drought is proof of a change in the climate,'' he added. ``The drought in the 1840s was as long as this one and that was before the buildup of carbon dioxide in the atmosphere.''

Scientists generally agree that increased atmospheric carbon dioxide, caused by the burning of fossil fuels, eventually will warm the world's climate. But there is controversy over whether the warming has actually begun.

The immediate cause of the California drought is persistent areas of high pressure over the West Coast or offshore in the Eastern Pacific Ocean. Storms arriving at California from the subtropics near Hawaii are weakened by the high pressure. And the jet stream from the stormy Gulf of Alaska splits around the high pressure, diverting storms into Alaska and British Columbia and - this year, anyway - into Mexico, missing California entirely.

``Washington state (on the southern edge of the storm track) is really about the only place on the West Coast that's had halfway decent precipitation,'' the National Weather Service's Wagner said. ``Even Oregon and Northern California have been getting only brief storms.''

But seeking global-scale causes beyond the regional high pressure has left scientists with a big puzzle.

``In all the drought cases, we've always had these high-pressure regimes,'' Cayan said. ``It's the one thing in common. But if you look further, there is no simple, single pattern.''

``It's not the same situation winter after winter that provokes our dryness. It's a very complex issue.''

When will California's ordeal end? The experts aren't guessing.

Although University of Arizona studies have found 20-year dry spells, they were invariably interrupted by occasional wet years. The longest string of consecutive dry years was six, from 1843 through 1848, Meko said.

In the absence of scientific explanations, the reassurance from the tree-ring record that in four centuries no drought has continued more than six years may be the only hopeful note there is.



The jet stream carrying storms from the Gulf of Alaska splits when it encounters high pressure off the coast. One branch heads into Alaska and British Columbia, with the southern edge sometimes brushing Washington state. The southern branch, in wet years, parallels the coast and delivers rain and snow to Northern California. But this winter it has been going south of California.


Persistent ridges of high pressure along the West Coast or in the Eastern Pacific have been present during each of California's dry winters. But conditions in the North Central Pacific vary from year to year, frustrating efforts to find an underlying cause for the draught.


High pressure weakens the ``Hawaiian connection,'' winds from the southwest that are usually California's major source of rain and snow. The winds, part of storms originating in the Pacific Ocean north of Hawaii, drop rain and snow when they encounter California's Sierra Nevada. In drought years the winds are less vigorous and deliver less moisture.

Seeding clouds, usually with silver iodide particles, sometimes can increase the amount of rain or snow by providing nuclei on which ice crystals can form. Some 15 agencies in California are trying to augment precipitation in the the mountains to increase the snowpack above reservoirs.



If you would like to read more about California's water problems, here are some sources:


``The Big Thirst,'' by Marc Reisner, Oct. 28, 1990.


by Marc Reisner, Penguin, 1987.


by William Kahrl, University of California Press, 1982.