A hydrometeorological streamflow-prediction model (HM model) developed for the North Cascades of Washington has been tested in the south-central Sierra Nevada of California. Twenty-four drainages ranging in mean altitude from 770 to 3,160 metres, including several of the major ones such as those of the Kern, Kings, and Merced Rivers, were examined. Eight U.S. National Oceanic and Atmospheric Administration precipitation stations were evaluated. Of these, three proved to be of significant value for nearly all the drainages used. Results are given for predictions on February 1, March 1, and April 1 of monthly runoff of five major drainages for the April-September season. Also demonstrated is the April 1 prediction of a daily hydrograph for the April-September season for 2 diverse years. The altitude distribution of storage and runoff, both observed and predicted, is determined by using several drainages with different area-altitude profiles. Results of this calculation for two drainages show that, on the average, approximately 50 percent of the April-July runoff originates above 2,800 m. The influence of subsequent precipitation on prediction accuracy is determined by relating prediction error and actual precipitation occurring after the prediction day. Results for three basins show that about 75 percent of the error of a January-September prediction on January 1 is due to precipitation occurring during the prediction season. Comparisons of prediction accuracy are made for five major drainages: the Kern River near Kernville; the Kings River below North Fork, near Trimmer (inflow to Pine Flat Dam); the Kings River at Piedra; the Merced River at Pohono Bridge, near Yosemite; and the Merced River below Merced Falls Dam, near Snelling. The accuracy of the HM model appears to be about 24 percent higher than existing operational methods in predicting the April-July runoff on April 1.
