Blowing Snow Fluxes over Complex Terrain
Richard Essery1, Long Li1, and John Pomeroy2
Significant amounts of sublimation can occur from blowing snow in open, windswept environments,
and redistribution of snow by wind leads to variations in depth that influence the depletion of snow
during melt. Transport and sublimation rates increase rapidly with increasing wind speed and so are
highly sensitive to wind speed variations. Wind speed, in turn, is strongly influenced by variations in
topography and surface roughness. In this study, a distributed model is used to investigate the scaling
of blowing snow fluxes over complex terrain.
The distributed model is derived from a physically based model of blowing snow over homogeneous
terrain. To allow the model to be run with high spatial and temporal resolution (40-meter and 30-
minute), a simplified version is introduced which, while lacking a physical basis, can reproduce the
blowing snow model results closely with much greater computational efficiency. Wind speed maps
are produced for an area using a terrain windflow model. Inputs required are digital elevation and
vegetation maps and time series of temperature, humidity, and wind speed.
The model has been run using data from an arctic tundra basin. Area-average sublimation is found to
be only slightly increased over that predicted by the blowing snow model for uniform terrain, but the
cumulative influences of transport generate large variations in snow depth. This redistribution is
sensitive to the ad hoc representation used for the response of transport to changes in wind speed;
further work is required on this problem.
Distributed models are unsuitable for large-scale applications, and scaling methods have to be used.
From the equations used by the windflow model, approximate relationships are developed between
topography and the distribution of wind speeds over an area. These relationships are used to model
the statistical and fractal properties of redistributed snow covers.
1
Division of Hydrology, University of Saskatchewan, Saskatoon, Canada
2
National Hydrology Research Centre, Saskatoon, Canada
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