Anemometric versus Geometric Snow Surface Roughness Length Comparison for a Shallow Snowpack

When applied to a snow-covered surface, aerodynamic roughness length (z₀) is typically considered as a static parameter within energy equations, especially when incorporated in hydrological and atmospheric models. However, field observations of z₀ have shown that z₀ is a dynamic value and should be integrated into the equations and modeled as such. The dynamics of the snow surface has been found to change spatially and temporally based on the underlying topography, vegetation, and meteorological factors. The objective of this study was to compare the two primary methods of calculating z₀: anemometric and geometric. Three study areas in different landscapes near Fort Collins, Colorado were measured over two winter seasons to analyze the variations of z₀. Each site had a meteorological tower to compute the anemometric z₀ and was easily accessible to use LiDAR to measure the snow surface to compute the geometric z₀ during periods of snow accumulation and snow melt. Our research findings research should assist in improving forecasting of snowpack water yield, land surface and atmospheric energy models, and incorporating a dynamic z₀ roughness across a variety of scales.