Insights into the physical processes controlling correlations between snow distribution and terrain properties

This study investigates causes behind correlations between snow and terrain properties in a 27 km(2) mountain watershed. Whereas terrain correlations reveal where snow resides, the physical processes responsible for correlations can be ambiguous. We conducted biweekly snow surveys at small transect scales to provide insight into late-season correlations at the basin scale. The evolving parameters of transect variograms reveal the interplay between differential accumulation and differential ablation that is responsible for correlations between snow and terrain properties including elevation, aspect, and canopy density. Elevation-induced differential accumulation imposes a persistent source of varariabity at the basin scale, but is not sufficient to explain the elevational distribution of snow water equivalent (SWE) on the ground. Differential ablation, with earlier and more frequent ablation at lower elevations, steepens the SWE-elevation gradient through the season. Correlations with aspect are primarily controlled by differences in solar loading. Aspect related redistribution of precipitation by wind, however, is important early in the season. Forested sites hold more snow than nonforested sites at the basin scale due to differences in ablation processes, while open areas within forested sites hold more snow than covered areas due to interception. However, as the season progresses energetic differences between open and covered areas within forested sites cause differences induced by interception to diminish. Results of this study can help determine which accumulation and ablation processes must be represented explicitly and which can be parameterized in models of snow dynamics.