INCREASING VARIABILITY IN CALIFORNIA PRECIPITATION.

Most of California experienced the severest dry spell on record in 1976–77; 1978 was one of its wettest rainy seasons. The economic and environmental impacts of the drought were significant. Comparisons of nonoverlapping, twenty-year periods between 1921 and 1977 produced few statistically significant differences in either means or variances. The probability of occurrence of extreme seasonal precipitation increased in the northern two-thirds of the state in the period 1961–77 relative to the period 1921–60, but decreased in the south. The chance of getting a total seasonal precipitation less than forty-three percent of the mean in any one year in the Sacramento Valley and the North and Central Coast regions since 1961 has increased to 1 in 15 from 1 in 20 in the period 1921–40 and 1 in 21 or 25 over the whole period of record. The period 1961–77 is statistically more similar to 1860–80 than to either 1921–40 or 1941–60. No relationships could be established between hemispheric warming and cooling and precipitation variability in California. [ABSTRACT FROM AUTHOR]