How does a dynamic surface roughness affect snowpack modeling?

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 (z_0-A), using a wind profile, and geometrically (z_0-G), measuring surface geometry. Calculated z_0-A values were between 1.03 × 10⁻⁶ to 0.12 m. The z_0-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 z_0-G values of 0.26, 0.08, and 0.01 m, respectively. Therefore, as the resolution coarsened, the z_0-G values decreased. Lastly, these calculated z_0-G values, a variable run, using weekly measured z_0-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.