Newly Implemented Snow-Vegetation Representation in the Community Land Model

Abstract:

Boreal forests are a major source of surface albedo feedback spread in CMIP5 models. We’ve incorporated improvements into the Community Land Model (CLM) vegetation canopy snow treatment in order to more realistically represent boreal forest canopy albedo. Current CLM hydrology does not differentiate the phase of precipitation intercepted by vegetation. To represent canopy snow, there is a sharp temperature-dependent switch in canopy albedo parameters at 0 K. Snow immediately ceases to exist when vegetation temperature rises above freezing. We’ve separated phases in the CLM vegetation hydrology, allowing snow to have its own storage maximum and interception treatment. Wind and melt based unloading terms have also been incorporated to more accurately simulate canopy processes, creating a path for canopy snow loss in freezing temperatures. To evaluate the new treatment, we compared singe-point CLM 4.5 simulations with accumulated canopy snow mass measurements from Umpqua Forest, Oregon. Additionally, we have considered the effects of modifying snow cover fraction and latent heat fluxes from phase changes. Global CLM simulations evaluate the climatic differences between existing CLM and CLM with the new implementations for boreal forests.