Evergreen canopies have high winter leaf areas and consequently can intercept a large proportion of the annual snowfall. In cold climates, this intercepted snow is stored in the canopy for as long as several months, where it is well-exposed to the atmosphere and subject to relatively high sublimation rates compared to snow surfaces on the ground. A GEWEX experiment in the southern boreal forest of western Canada has detailed the intercepted snow load in coniferous canopies, snow mass balance and energy balance over several winters. The field results show that:

i) 28% to 65% of cumulative seasonal snowfall can be intercepted and stored in coniferous canopies in mid-winter, and

ii) 30% to 45% of annual snowfall sublimates due to its exposure as intercepted snow.

A series of physically-based algorithms has been developed to describe the accumulation and storage of intercepted snow in forest canopies. These algorithms are unique in that they account for features of interception in cold climates such as declining interception efficiency with increasing snow load and temperature. Leaf area index, canopy closure and tree species are used to relate interception efficiency to quantitative stand characteristics. To determine sublimation rates, turbulent heat and mass transfer routines described by Pomeroy and Gray (1995) and applied using a fractal snow scaling technique (Pomeroy and Schmidt, 1993) have been applied to the calculated snow loads. The coupled accumulation/sublimation model is used to describe a sequence of canopy snow storage and sublimation events in the winter of 1995-96. The coupled model of snow storage and sublimation from the canopy is physically-based, uncalibrated and reasonably successful in estimating snow sublimation loss. It can thus aid in the development of land surface process schemes and hydrological models that are suitable for operation in northern evergreen forests. The model also demonstrates the usefulness of intensive field campaigns in developing snow models.

# Division of Hydrology, Dept. Of Agricultural and Bioresource Engineering
University of Saskatchewan, Saskatoon, Sask. S7N 0W0