Spatial and Temporal Variation of Net Snow Accumulation in a Small Alpine Watershed, Emerald Lake Basin, Sierra Nevada, California, U.S.A.

Abstract

Distribution of snow-water equivalence (SWE) in the Emerald Lake watershed located in Sequoia National Park, California, U.S.A, was examined during the 1987 water year. Elevations at this site range from 2780 to 3416 m a.s.l., and the total watershed area is about 122 ha. A stratified sampling scheme was evaluated by identifying and mapping zones of similar snow properties, based on topographic parameters that account for variations in both accumulation and ablation of snow. Elevation, slope, and radiation values calculated from a digital elevation model were used to identify these zones. Field measurements of SWE were combined with characteristics of the sample locations and clustered to identify similar classes of SWE. The entire basin was then partitioned into zones for each set of survey data. The topographic parameters of the basin used in classification, namely slope and elevation, are constant in time and did not change between survey dates. The radiation data showed temporal variability providing a physically justified basis for changes in SWE distribution through time. Although results do not identify which of the classification attempts is superior to the others, net radiation is clearly of primary importance, and slope and elevation appear to be important to a lesser degree. The peak accumulation for the 1987 water year was 598 mm SWE, which is about half the 50 year mean.