DYNAMIC SIMULATION OF PHASE-CHANGES IN SNOWPACKS AND SOILS

Phase changes of water in snowpacks and soils are controlled mainly by the short-term dynamics of energy exchange with the atmosphere. The accurate reproduction of the exchange processes is thus necessary to the reproduction of freezing and thawing, and of consequent water movement, in ecosystem simulations models. In the model used for this study, energy exchange between the atmosphere and the surfaces of single-layered snowpacks and multiple-layered soils were calculated from recorded meteorological data and from measured physical properties of snowpacks and soils. The consequent absorption and transmission of energy through the snowpack and soil media were used estimate the dynamics of phase changes in the snowpack and soil water. The hourly behaviour of the model allowed it to reproduce, to within 50 W m-2, the diurnal patterns of energy exchange recorded over a melting snowpack and, to within 1-degrees-C, the diurnal soil temperatures recorded at depths of 0.05 and 0.15 m in a thawing soil profile. The seasonal behaviour of the model allowed it to reproduce overwinter patterns of accumulation and disappearance of a snowpack to within 50 mm, and those of maximum and minimum daily soil temperatures at depths of 0.05 and 0.15 m to within 1-degrees-C. Models that function at this level of detail are useful in estimating the effects of slope, aspect, residue cover, and other surface characteristics on snowmelt and soil warming. With higher spatial resolution in parameterizing snowpack functions for hydraulic and thermal conductivity, these models may be used to represent multilayered snowpacks.