Distributed Simulation of Snowcover Mass and Energy Balance
in the Boreal Forest
Timothy Link1 and Danny Marks2
The accurate distributed simulation of snowpack deposition and ablation beneath forest canopies is
complicated by the fact that vegetation canopies strongly affect the snow surface energy balance.
The canopy alters the radiation balance of the snowcover and reduces the wind speed at the snow
surface. Simple canopy adjustment algorithms for solar and thermal radiation and wind speed are
used in conjunction with topographically corrected radiation estimates and commonly available
land-cover classifications (canopy species and height) to distribute subcanopy solar and thermal
radiation, air and soil temperature, humidity, wind speed, and precipitation. The spatially distributed
climate surfaces are used to drive a 2-layer coupled energy- and mass-balance snowmelt model over
the BOREAS northern and southern study areas for the 19941995 snow season. Model results are
validated using both automatic and manually collected snow-depth data. The simulated timing and
rate of snowpack development and ablation at both study areas are well represented beneath the
canopy types where validation data are present.
Results from the distributed snowcover simulations indicate that canopy structure can delay seasonal
snowmelt in forested areas up to three weeks, relative to open areas. The differences primarily result
from net snowcover radiation variations attributed to altered solar and thermal radiation regimes
beneath forest canopies. Variations in snowmelt also result from differences in turbulent heat fluxes
caused by reduced windspeeds within forest canopies. Other ablation differences arise from subtle
topographically controlled radiation variations. Rigorous evaluation of model performance beneath
the full range of canopy types requires information regarding the spatial distribution of snow-cov-
ered areas during the ablation period. This study demonstrates that given basic landcover parame-
ters, relatively simple canopy adjustments coupled with an energy balance model can be used to
estimate climate conditions and snowcover processes over heterogeneous boreal regions.
1 Oregon State University, USEPA-NHEERL, 200 SW 35th Street, Corvallis, Oregon 97333, USA
2 U.S.D.A.-Agricultural Research Service, Northwest Watershed Research Center, 800 Park Boulevard, Suite
105, Boise, Idaho 83712, USA
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