Abstract
Abstract. A modelling study was undertaken to evaluate the contribution of sublimation to an alpine snow mass balance in the Canadian Rocky Mountains. Snow redistribution and sublimation by wind, snowpack sublimation and snowmelt were simulated for two winters over an alpine ridge transect located in the Canada Rocky Mountains. The resulting snowcover regimes were compared to those from manual snow surveys. Simulations were performed using physically based blowing snow (PBSM) and snowpack ablation (SNOBAL) models. A hydrological response unit (HRU)-based spatial discretization was used rather than a more computationally expensive fully-distributed one. The HRUs were set up to follow an aerodynamic sequence, whereby eroded snow was transported from windswept, upwind HRUs to drift accumulating, downwind HRUs. That snow redistribution by wind can be adequately simulated in computationally efficient HRUs over this ridge has important implications for representing snow transport in large-scale hydrology models and land surface schemes. Alpine snow sublimation losses, in particular blowing snow sublimation losses, were significant. Snow mass losses to sublimation as a percentage of cumulative snowfall were estimated to be 20–32% with the blowing snow sublimation loss amounting to 17–19% of cumulative snowfall. This estimate is considered to be a conservative estimate of the blowing snow sublimation loss in the Canadian Rocky Mountains because the study transect is located in the low alpine zone where the topography is more moderate than the high alpine zone and windflow separation was not observed. An examination of the suitability of PBSM's sublimation estimates in this environment and of the importance of estimating blowing snow sublimation on the simulated snow accumulation regime was conducted by omitting sublimation calculations. Snow accumulation in HRUs was overestimated by 30% when neglecting blowing snow sublimation calculations.
Highlights
Snowpack depth and density in the alpine zone of high mountains exert a strong control on the magnitude, timing and duration of snowmelt as well as directly influencing alpine ecology and avalanche formation (Jones et al, 2001)
Where SWEsim and SWEobs are the simulated and observed snow water equivalent (SWE), respectively. α is the fractional area of the hydrological response unit (HRU). α is included so that the model evaluation statistics reflect the relative size of different HRUs that make up the FR transect
Snow redistribution and sublimation by wind, snowpack sublimation, snowmelt and the resulting accumulation regimes were simulated over HRUs representing a transect along an alpine ridge in the Canadian Rockies
Summary
Snowpack depth and density in the alpine zone of high mountains exert a strong control on the magnitude, timing and duration of snowmelt as well as directly influencing alpine ecology and avalanche formation (Jones et al, 2001). Snowcover increases the surface albedo and provides a colder surface to interact with the atmosphere compared to snow-free zones. There are marked differences in energy and moisture fluxes over snow-covered and snow-free surfaces, which have implications for evapotranspiration, permafrost, and glaciers. Snowpack and snowcover characteristics in alpine zones are strongly influenced by wind through the action of wind in entraining, transporting and sublimating snow (Dyunin and Kotlyakov, 1980; Fohn, 1980; Schmidt et al, 1984; Meister, 1989; Pomeroy, 1991). Since snowmelt has an extremely important role in regulating annual runoff, these winter sublimation losses can have an important effect
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