How does a dynamic surface roughness affect snowpack modeling?

Abstract

The SNOWPACK model is a cryosphere model which incorporates several environmental model parameters, one of which being the aerodynamic roughness length (z0). The z0 is considered a static parameter, however, research has shown that the z0 of the surface is variable due to the changing nature of the snowpack surface throughout the winter season. This study highlights the sensitivity of the z0 within the SNOWPACK model based on the outputs of sublimation, SWE, and sensible heat. The z0 values were calculated in two ways, anemometrically (z0-A), using a wind profile, and geometrically (z0-G), measuring surface geometry. Calculated z0-A values were between 1.03 × 10−6 to 0.12 m. The z0-G values were calculated from a terrestrial lidar scan using various resolution values of post-process resolutions. These resolutions of 0.01, 0.1, and 1 m resulted in z0-G values of 0.26, 0.08, and 0.01 m, respectively. Therefore, as the resolution coarsened, the z0-G values decreased. Lastly, these calculated z0-G values, a variable run, using weekly measured z0-G values, and 0.002 (SNOWPACK default), 0.02, and 0.2 m values were incorporated into the SNOWPACK model. When applied, cumulative sublimation, SWE, and sensible heat outputs varied by 131%, −71%, and −49%, when compared to the default z0 value used within the model.