A century of precipitation variability along the pacific coast of North America and its impact

Precipitation data at seven stations along the west coast of North America, dating back to 1851 at some stations, are synthesized by means of empirical orthogonal function analysis. Characteristics of runs of generally wet and generally dry conditions are quantified. A significant change in precipitation regime, lasting 41 yrs, occurred in the middle of this century and could return in the future. Drought occurrences, similar to midwestern United States episodes, appear in the data, but are not statistically verifiable. A single example of the interaction of precipitation variability and society is given. Man's actions amplify the impact of variability on hydroelectric power generation in two ways: Society adapts itself rapidly to transient beneficial conditions, creating a false sense of well-being; technology expands to consume maximum available resources, decreasing system resilience.