Elevational and latitudinal patterns of snow accumulation departures from normal in the Sierra Nevada

Summary

This study investigates whether snowpack water equivalents in the northern and southern parts of the Sierra Nevada, or at high and low elevations in that range, have a tendency to acquire opposite departures from normal. Data from 28 snow courses were subjected to principal components analysis for February 1 and April 1 observations for the years 1954–1983. The first principal component indicated that there is a great deal of uniformity within the Sierra in terms of above- or below-normal accumulations in a given year. A second component had loadings depicting a pattern whereby high and low elevation sites have opposite departures from normal. Over the entire period of record this pattern accounted for a small percentage of the total variance, although in some years it was conspicuous. A third component indicated a tendency for northern and southern sites to have opposite departures from normal. Correlation coefficients were also obtained for 42 snow courses from 5 basins to further compare the relative influence of elevation and spatial separation. The correlation coefficients showed that elevation exerts a greater influence on the variation in departures from normal than does distance within drainage basins. These elevational differences in accumulation may have important consequences with regard to the timing of runoff and the availability of water stored in reservoirs.