Unprecedented 7th Year of State Drought Forecast : Water: Hydrologists say dry spell would exceed those found in tree-ring records dating as far back as 1560.

If water experts are correct, Californians may be on the verge of experiencing something that has not happened in at least four centuries--a seventh year of drought.

Using 90 years of written data and tree-ring records dating back to 1560, state hydrologists have determined that there is a high probability that this winter, like the six preceding it, will be dry.

“We will be making history,” said Maurice Roos, chief hydrologist for the Department of Water Resources. “For Northern California it will definitely be the worst seven years in our measured record.”

Roos, who has been analyzing the state’s water needs for 35 years, said the “most likely assumption” is that this winter’s storms will produce about 14 million acre-feet of runoff in the Sacramento River Basin--compared to a high of 37.7 million in 1983 and a low of 5.1 million in 1977.

To reach that estimate, Roos said, his researchers do not look solely at drought patterns down through the years. Rather, they take into account past dry years, wet years and normal years dating back to the 16th Century and estimate the winter to come based on laws of probability. The probability of any year being a dry year is 30%, a wet year, 30%, and a normal year, 40%. But the probability of drought conditions increases to more than 50% in any year after a critically dry year, such as the 1991-92 water year, according to Roos.

If the prediction holds, he said, the 1992-93 water year would be classed as dry but would be somewhat wetter than five of the six preceding years that fell in the critically dry category.

A seventh year of drought could prove to be the most difficult for Californians to deal with.

California is entering this year’s critical winter storm season with water storage in the state’s 155 reservoirs at near-record low levels and competing demands for environmental protection soaring.

Virtually all of the water in storage is a rock-bottom emergency supply that will have to remain untapped in 1993, leaving the state’s 30 million residents to depend almost exclusively on what falls from the sky.

“We’re at the mercy of God’s blessing this year,” said Roos.

“The need for a better-than-average rainfall is more severe now than at any time in the last six years,” said Jay Malinowski, assistant chief of operations for the Metropolitan Water District. “We’ve been putting water on our MasterCard; we’ve been borrowing from the future” by pulling down reservoir storage to bolster deliveries during the drought, he said.

The cumulative effects of the past six dry years have left the soil parched and the ground-water basins so low that as much as 10% of any precipitation, it is believed, would simply be soaked up before it could run off into rivers and streams and be captured in the state’s reservoirs and aqueducts.

New restrictions on pumping water from the Sacramento River Delta, intended to protect endangered species of delta smelt and winter-run salmon, will further reduce available supplies, officials said. And legal restrictions on the diversion of water from the Mono Lake Basin and pumping from the Owens Valley also will limit the availability of water this year.

“This year will be fundamentally different” because of the increased environmental restrictions, said Stephen Hall, incoming executive director of the Assn. of California Water Agencies.

David Kennedy, director of the state Department of Water Resources, said that most of the water in the state’s largest reservoir at Lake Oroville “is basically tied up with delta (environmental) problems and the salmon.”

A dry or even average winter storm season could lead to the resumption of mandatory water conservation programs and possibly severe cutbacks in deliveries to agriculture and urban users, officials said.

Although the 1992-93 water year, which runs Oct. 1 to Sept. 30, is just six weeks old, many in the water business believe there are already signs that Roos’ predictions may be correct.

Rain and snowfall in October was at 125% of normal, but it is an insignificant amount of the yearly total, representing only about 6% of the annual precipitation. So far this month, in which about 13% of annual rain and snowfall is recorded in normal years, precipitation has been below normal.

“It hasn’t started off with a bang,” said Roos.

For California, the important months for water are November through March, when about three-quarters of all snow and rain falls. Most of that precipitation falls in the Sierra Nevada, flows to the Sacramento-San Joaquin River Delta or the Owens Valley and is shipped via aqueducts and river systems primarily to farms and urban centers in Southern California.

For Roos’ purposes, history comes in two forms--written records dating back to 1906 that show precise rainfall measurements, and tree-ring studies that enable researchers to reconstruct rainfall patterns for a longer sweep in time. By measuring tree-ring widths, experts can generally determine when droughts occurred and how long they lasted.

From his examination of historical records, Roos found two droughts that seem similar to the one that now grips California--a dry period from 1929 through 1934 and another from 1836 through 1846.

The 1836 drought, which was interrupted by one wet year in 1842, was finally broken by the famous snowfall of 1846-47 that trapped 87 immigrants in the High Sierra. Led by George Donner, many of the pioneers perished in the harsh winter while others survived by resorting to cannibalism.

For the longer look back in time, the tree-ring technique, using trees hundreds of years old, is considered the best gauge of dry years. Researchers at the University of Arizona’s tree-ring laboratory have established precipitation patterns dating back to the middle 1550s, and have concluded that at no time did a drought last more than the current dry spell in Northern California. Droughts in past centuries have lasted longer, however, in Southern California.

Meteorologists also make long-term predictions about the precipitation, but most water officials say flipping a coin--or turning to the historical probabilities as Roos has--is usually a safer bet.

Still, a variety of private and governmental forecasters have made 90-day outlooks that are in general forecasting normal rainfall statewide, with above-normal temperatures, through January.

More than half of all water consumed in Southern California is imported from Northern California or the Colorado River. Although some rainfall in Southern California is saved in ground-water basins in the San Fernando Valley, San Gabriel Valley and Orange County, most local precipitation flows into the sea.

Currently, water storage in reservoirs statewide is at 56% of normal, or 12.67 million acre-feet, according to the state Department of Water Resources. An acre-foot covers one acre of land one foot deep in water--or enough to supply about three families for a year.

The state’s current storage supply is down about 5%, or 1.1 million acre-feet, from last year and by more than 50%, or 14.1 million acre feet, from 1986--before the unusual six-year drought began. Storage is at its lowest level since the drought of 1977--the driest year on record in California, according to the Department of Water Resources.

Most water officials say that the storage level at this point in the drought is testimony to the strength of the state’s water system, rather than an indictment of any weakness.

“I think it is extraordinary that we are not in worse shape,” said Hall.

Because extended droughts are unusual in California--and a seven-year drought is unprecedented--Malinowski said that water agencies felt secure in using the water stored in reservoirs to bolster supplies in the past six years. They assumed the drought would end before they exhausted their usable reservoir supplies.

“Call it a gamble,” said Malinowski of the MWD. “But it’s the hard choice you have to make.”

Mike Gage, president of the Los Angeles Department of Water and Power Commission, said, “We could have probably saved more water, but second-guessing doesn’t have a lot of merit. This drought is unprecedented in modern times. We are charting new turf.”

Water officials are busily mapping plans to deal with the expected shortfall in supplies in the coming year.

At the MWD, which provides about half of all water consumed in Southern California from the state system and the Colorado River, officials are hoping to purchase water from farmers and other water districts around the state.

Just last week, the MWD board approved the first of what they hope will be a series of such deals. The agency signed a one-year agreement to purchase 12,000 acre-feet of water from the Dudley Ridge Water District in the San Joaquin Valley.

Earlier, the MWD had made purchases from the state’s water bank, by which the Department of Water Resources buys supplies primarily from farmers and resells it primarily to urban users.

Recent federal legislation theoretically makes it easier for farmers and water districts that are part of the Central Valley Project to sell their water supplies to urban users. But Hall, among others, questions just how much water will be made available. He said that many farmers will need much of their allocation from the project to make it through the year. Many of them have been using their ground-water supplies to supplement CVP deliveries and those, too, are running low.

But even if water is made available for sale, environmental restrictions may make its delivery difficult or impossible in a dry year, officials said.

Hall said the problem is in the Sacramento River Delta, where federal officials will be restricting pumping into reservoirs and aqueducts during the salmon run and smelt spawn.

Many of the potential sellers will be from north of the delta, and the likely buyers from the south. Much of the water sold would have to flow through the delta, where the environmental restrictions apply, then be pumped into aqueducts heading south.

“If we can’t pump the water purchased, it doesn’t do us much good,” said Duane Georgeson, assistant general manager of the MWD.

California’s Water Reserves

Storage in California’s 155 major water reservoirs is near an all-time low. The chart shows the capacity of the state’s reservoir system, the average storage level and the amount of water stored in each of the drought years between 1987 and 1992. Also shown are the record low storage levels of 1976 and 1977, the driest years in state history.

* An acre-foot covers one acre of land, one foot deep. It is enough to supply three families for one year.

Source: California Department of Water Resources.