Forecasting seasonal precipitation in California: Its relation to electric power production

From an analysis of precipitation in significant districts of California, it is possible to deduce cycles or recurrences of from 2 to 3 years, from 5 to 6 years, and from 20 to 26 years, these being superimposed upon a longer or secular period of from 50 to 60 years. In this manner an estimate can be made of the rainfall to be expected over a relatively long period — as for the next 10 years; at the present moment, indications point towards greater precipitation and run-off in the period 1930–40 than in the preceding decade. Such estimates are of tremendous economic importance to agricultural interests and irrigation projects — such as the Hoover Dam, which involves storage of vast quantities of water for the creation of electric power and for supplying water to Los Angeles and other portions of southern California. In order to forecast for a year or season at a lime, it is necessary to make a statistical study of meteorological elements (including ocean temperatures) over a wide area during the preceding quarter or six months. Predictions of California rainfall based on the temperatures taken at inshore stations on the South Coast during the summer have been sufficiently successful to justify a continuation of the work. By using composite indexes, it is possible to increase the degree of correlation between computed and observed precipitation to a reasonably high figure.