Snow, vegetation, and asymmetric canyons in the Canadian version of the Town Energy Balance (TEB) urban-canopy scheme

A new Canadian version of the Town Energy Balance (TEB) scheme is being developed at Environment Canada (EC) in an effort to better represent the urban canopy and its impact on the atmosphere through fluxes of heat, moisture, and momentum within the Global Environmental Multiscale (GEM) meteorological model. In essence, TEB represents the city environment as an "urban canyon" where longwave and solar radiation is absorbed, reflected, and re-radiated by roofs, walls, and roads. In EC's current implementation of TEB, this urban canyon is symmetric, with identical configurations for canyons at the front and at the back of a row of buildings. Moreover, the bottom surface of all canyons (i.e., the road component) is always impervious. In this study, EC's TEB scheme has been modified to allow for asymmetric street canyons and for a better representation of natural surfaces (bare soil and vegetation, but not water) within urban canyons. The vegetation and soil surfaces in the new TEB are simulated using the Interaction Soil Biosphere Atmosphere (ISBA) land surface scheme already in use operationally within GEM. The representation of snow, in the new TEB, is also modified by using a common sub-module currently included in ISBA and based on a single-layer snow model with prognostic evolution of snow temperatures, albedo, density, and liquid water content in the snow pack. Preliminary results from these modifications will be presented at the symposium.