Development of snow surveying in California

The present water use in California for irrigation, power and municipal purposes depends on reliable information on the amount of water which will be contributed by the mountain snow pack in the spring. The existing program of snow surveys was initiated in 1929. The extent of the California Cooperative Snow Surveys is presented, with 175 active snow courses covering 24 watersheds. Forecasting is based on results of snow surveys conducted in April and assumes that average conditions will prevail during the following months. Forecasts of April 1 are modified and corrections published on May 1 when abnormal precipitation during the early runoff period occurs. The ‘Direct method curve’ used to modify accurately the original estimate is illustrated using the Upper San Joaquin River watershed as an example. The Direct method of forecasting was made possible by the 10 years of existing records on snow courses and runoff, and provided sufficient data to establish a relationship between snow survey data and runoff data with some degree of accuracy, without becoming involved with percent of normals.