Effect of covariance between ablation and snow water equivalent on depletion of snow-covered area in a forest

Abstract

The influence of the spatial distribution of snow water equivalent and covariance between spatial distributions of ablation and snow water equivalent on depletion of snowcover was investigated in the boreal forest of central Saskatchewan. Canada. Changes in the spatial distributions of snow water equivalent were measured before and during melt in five stands, ranked by canopy density as: black spruce, jack pine, mixed wood, burned and recent clear-cut. The pre-melt frequency distribution of snow water equivalent within forest stands was found to fit a log-normal distribution. Higher variability in snow water equivalent resulted in earlier exposure of ground under spatially uniform melt simulations, confirming the previous findings of others for open environments. The spatial distribution of daily ablation within stands was found, however, to be correlated inversely to the distribution of snow water equivalent. This negative covariance between snow water equivalent and ablation further accelerated snow cover depletion. The combined acceleration as a result of variance of snow water equivalent and covariance with ablation was greatest in mixed-wood stands and smallest in burned and spruce stands. Simulations that included the within-stand covariance of ablation and snow water equivalent showed improved fit with measured data over those that only considered the effect of the distribution of snow water equivalent on snow-cover depletion.