Matt MacDonald will be defending his MSc, entitled Hydrological response unit-based blowing snow modelling over mountainous terrain on Monday, 18 October at 1:00 pm, in room 144 Kirk Hall
Wind transport and sublimation of snow are common phenomena across high altitude and latitude cold regions and play important roles in hydrological and atmospheric water and energy budgets. A physically based blowing snow model (PBSM) was used to model snow redistribution and sublimation by wind over two mountainous sites: Fisera Ridge in the Rocky Mountain Front Ranges in Alberta, and Granger Basin in the Yukon Territory. Two models were used to run PBSM: the Cold Regions Hydrological Modelling Platform (CRHM) and Environment Canada’s MESH. Blowing snow algorithms were incorporated into MESH to create MESH-PBSM. CRHM, MESH and MESH-PBSM were used to simulate the evolution of snowcover in hydrological response units (HRUs) over the sites.
To test the models over a relatively simple sequence of mountain topography, simulations were run over Fisera Ridge. Simulations with CRHM were performed using two sets of wind speed forcing: observed wind speed, and modelled wind speed from an empirical model. Best results were obtained when using the observed forcing. The windflow model performed poorly and blowing snow sublimation, snowpack melt and sublimation quantities were considerably overestimated. MESH-PBSM was applied over these same HRUs and snow accumulation was adequately simulated up until the spring melt period.
To parameterize snow redistribution in a mountain basin, snow redistribution was calculated over Granger Basin. Three inter-HRU snow redistribution schemes were evaluated. CRHM results showed that snow accumulation can be most accurately simulated when taking into account wind direction and HRU aerodynamic characteristics, along with the spatial arrangement of HRUs. As snow transport scales with the fourth power of wind speed (u4), inter-HRU snow redistribution factors can be established according to the predominant u4 direction over a model period or can change at model time steps according to input wind directions. MESH and MESH-PBSM were applied over these same HRUs. MESH-PBSM provided markedly better results than MESH.
That snow redistribution by wind can be simulated in computationally efficient HRUs over mountainous terrain has implications for representing snow transport in large-scale hydrology models. Blowing snow caused snow accumulation to vary from 10% to 161% of snowfall, and blowing snow sublimation losses ranged from 10 to 37% of seasonal snowfall.