Dynamic snow surface aerodynamic roughness lengths (z0) characterized by snow depths using LIDAR

A shallow, seasonal snowpack is rarely homogeneous in depth, layer
characteristics, or surface structure throughout an entire winter.
Aerodynamic roughness length (z0) is typically considered a static
parameter within hydrologic and atmospheric models. However, observations
have shown that z0 is a dynamic variable, necessitating accurate spatial
and temporal measurements of z0. Terrestrial LiDAR data were collected at
nine different study sites in northwest Colorado from the 2019-2020 winter
season to observe variability of the snowpack surface. Geometric z0 and
snow depth (ds) observation over 112 site visits illustrated a change in
z0 as a function of ds. Values of z0 decrease during initial snow
accumulation, as the snow conforms to the underlying terrain. Once the
snowpack is sufficiently deep, which depends on the height of the ground
surface roughness features, the surface becomes more uniform. As melt
begins, z0 increases, when the snow surface becomes more irregular. The
correlation varied spatially and temporally though; it was
obscured by snowpack surface modifications, such as the presence of
vegetation, anthropogenic or ecologic influence. The rate of
change in the z0 versus ds correlation was almost constant,
regardless of the initial roughness conditions that only affected the
initial z0.