Results of Ten Years of Cloud Seeding in Santa Clara County, California

Abstract

Ten seasons of commercial cloud seeding in Santa Clara County, California, are evaluated using target and control stations selected in 1955. Comparison of the linear regressions of target rainfall upon control rainfall, using seasonal totals, for the seeded winters and for ten immediately preceding ones gives evidence for a net increase in target precipitation. Examination of the rainfall distribution within the target area, which was not a part of the original evaluation plan, shows that seeding effects are concentrated downwind of the highest part of the Santa Cruz Mountains, which form the southwestern boundary of the target area, and suggests that they are limited to periods of convective instability.