Impacts of snow surface aerodynamic resistance on snow water equivalent simulations in forested regions

The aerodynamic resistance at the snow surface (r_as) has an influence on the snowpack energy balance. However, there are no widely accepted approaches for parameterizing r_as in forested regions. In this study, we derived r_as under the influence of forest vegetation for five cases that depend on the canopy height and structure. Three parameterization schemes for r_as were then integrated into a distributed hydrologic model: (1) the aerodynamic resistance above the canopy, ignoring the canopy structure effects on r_as, (2) the full aerodynamic resistance formulation for the different canopy height cases, and (3) a simplified formulation that only represented the lower trunk layer. Model simulations were conducted at six snow telemetry (SNOTEL) sites in the Verde River Watershed, Arizona, and evaluated with respect to snow water equivalent (SWE) product from the SNOTEL sites and a gridded product. Results revealed the importance of accurately parameterizing vegetation canopy structure when calculating r_as in forested regions. Cases where r_as included the vertical structure effects showed improved simulations of SWE across all sites. Finally, r_as is mostly determined by trunk layer aerodynamic resistance such that the simplified formulation is sufficient for representing forest canopy effects on r_as.