1990 Is Driest of Drought’s 4 Years : Climate: The snowpack is just 10% of normal. Fire, insect threats greatly increased by dry timber.

This is the most severe year of the current drought in California and the fifth-driest this century, state water officials said this week as the spring’s final survey found the winter snowpack has melted away early and reservoir levels are falling.

In most years, snowmelt in the Sierra Nevada and other mountains keeps replenishing reservoirs into the summer. But this spring the remaining snowpack is only 10% of normal, with bare earth showing at many stations where the snow depth is measured.

As a result, many of the reservoirs that get California’s cities and farms through the summer have stopped filling for the year and begun dropping.

“From now on it’s all downhill” until the next big snowfall or rainy season, presumably next winter, said Dean Thompson, an official in the State Drought Center in Sacramento.

Overall, water engineers say this year’s runoff into the Sacramento River system--which provides aqueducts with most of the water used in Southern California--totals only 40% of the annual average over the past 50 years.

In Santa Barbara County--which has declared a drought emergency--and other hard-hit areas along the central coast, runoff this year has been 10% of normal. Even on the state’s far north coast, where the climate resembles Oregon and Washington more than the rest of California, runoff is anticipated to be no better than 35% of normal.

Thus, 1990 is the worst of the four consecutive drought years that California has endured, and across the state the toll is beginning to mount.

Forestry experts say that insects could kill double the number of drought-weakened trees that died in California forests last year, when more than 1 million trees were lost. The prevalence of dry, dead wood in the forests increases the danger of wild fire, already extreme because lack of rainfall has turned brush and grasslands brown and crisp.

Water deliveries to farms in the Central Valley have been cut as much as 50%, forcing changes in crops and increased pumping of ground water. This is only the second time since the 1930s that drought has forced cuts for farms that rely on the federal Bureau of Reclamation for irrigation water.

In Southern California, water is especially short because the drought has reduced the flow from the Owens Valley area, a major source for the city of Los Angeles. A combination of drought and legal rulings also has cut the amount of water available from the Colorado River and the Mono Lake area of the eastern Sierra Nevada.

Mayor Tom Bradley has proposed a 10% mandatory cutback in water use by customers of the city Department of Water and Power. And the Metropolitan Water District of Southern California has called for voluntary reductions across the region to cope with an expected 12% shortfall.

The entire state could have survived this year’s dry condition without much pain if it had not come during one of the century’s driest cycles. The 8.2 million acre-feet of water in the Sacramento River system this year is still well above the 5.1 million acre-feet recorded in 1977, the worst drought year of the century in California.

The huge State Water Project reservoir at Oroville on the Feather River, which feeds the Sacramento, was also at a higher level on May 1 this year than it was on May 1, 1977.

But the last four years have been the driest in the northern half of the state--where the southern half gets most of its water--since a six-year drought finally broke in 1933.

Four years of below-normal snow and rainfall have dried up smaller reservoirs in Santa Barbara and San Luis Obispo counties. Many other reservoirs will enter this year’s hot season at well below normal levels and could reach critical levels during the summer, state officials say.