Experiments with cloud seeding began in the 1940s; today there are about a dozen programs to enhance precipitation, mostly snowfall in the mountains. Utilities that depend upon spring runoff to produce energy are some of the main sponsors. Pacific Gas and Electric Co. seeds clouds in the upper Mokelumne River headwaters; the Modesto Irrigation District seeds the upper Tuolumne River watershed. "Cloud seeding is not going to make up the deficit we have now - we have to have some storms," said Arlen Huggins, whose Reno-based Desert Research Institute seeds clouds using remotely operated ground units. But there may be more potential than the state has estimated: Huggins says small cloud-seeding research projects have shown precipitation can increase as much as 50 percent.

Throughout California, cloud seeders service about 13,000 square miles, an area nearly 10 times the size of San Joaquin County. The cost is about $3 million, making cloud seeding one of the cheaper ways to increase water supplies, compared with building dams and reservoirs. Seeding generates about 300,000 to 400,000 acre-feet of extra water, enough to cover the city of Stockton 8 to 10 feet deep, reports say. With the exception of far Northern California, there are few mountainous regions that aren't already targeted by cloud seeders, so there is little room to expand geographically. On the other hand, few of the cloud seeders likely have enough equipment to cover all their territory, said the research institute's Huggins.

The Northern California Power Agency's plan to cloud seed the upper Stanislaus River beginning this year met protests from environmentalists. The Central Sierra Environmental Resource Center was concerned about altering weather over designated wilderness areas and what effect the silver particles might have on declining frog populations. Cloud-seeding operations are only lightly regulated by the state; no permits are required, but seeders must inform the Department of Water Resources of their plans. State reports say silver has fairly low toxicity and that the amounts released in cloud seeding can't compare with exposure from industrial emissions or even tooth fillings.