Urban areas, through their high energy absorbing radiative properties, high level of human intervention and low availability of water for latent heat flux, have a surface energy budget that differs significantly from that of rural areas. Such differences can lead to changes in local circulation patterns, thereby complicating current weather prediction schemes. Further complexity is introduced in northern cities during the winter months when a blanket of snow acts as a potentially large water reservoir for latent heat dissipation and increases the shortwave albedo of horizontal surfaces. In this sense, snowfall has the effect of making the urban surface energy budget resemble the rural energy budget more closely.

“Dirty” urban environments and abrasive spreading and snow relocation practices quickly modify the snow's local properties (i.e. increasing the density, decreasing the albedo and redistributing the depth and the areal coverage). The temporal evolution of snow properties varies spatially at scales ranging from individual streets up to that of the entire city Previous urban studies performed in other northern cities have indicated these trends but to date no studies of winter energy budget and snow have taken place in a city as large as Montreal that receives as much winter snowfall.

This presentation will discuss the design and results from a snow measurement campaign conducted as part of the Environmental Prediction in Canadian Cities (EPiCC) network in Montreal, QC, Canada. Our observations focused on a densely populated urban residential area and a suburban, single-family-dwelling area of Montreal. Areal coverage, depth, density and albedo were tracked in ten types of snow cover on a weekly basis over the course of the winter of 2007-2008 and on an almost daily basis during two, ten-day intensive observation periods begun the day prior to, and immediately after, significant snowfall events.

Large spatial variations in snow density and depth were observed over very short distances across boundaries between snow cover types. Once snow had been displaced, the temporal evolution of bulk properties such as depth and density occurred slowly. However, albedo was observed to vary rapidly between snowfalls. This study will compare observations with the output from Environment Canada's snow simulation package that is part of the Interactions between Soil, Biosphere and Atmosphere (ISBA) land surface scheme, specially parameterized for different snow cover types.