资源环境科技发展态势分析平台

The leewards shores of the Laurentian Great Lakes are highly susceptible to lake-induced snowfall. During the late autumn and winter season, cold air advection over relatively warm lakes can induce instability in the lower planetary boundary layer (PBL), facilitating the exchange of moisture and energy fluxes and fuelling the development of snowfall. Snowfall in this region can have disastrous impacts on local communities such as the November 2014 Buffalo storm that caused 13 fatalities. This paper discusses historical snowfall trends along the Canadian leewards shores of Lakes Superior and Huron-Georgian Bay and explores several lake-induced predictor variables that may influence the snowfall trends. Spatio-temporal snowfall and total precipitation trends were computed for the 1980-2015 period over the Great Lakes Basin (GLB) using the Daymet (version 3) gridded estimated data set. Results show a significant decrease in snowfall, at a rate of 40cm/36years, and a significant decrease in total precipitation of 20mm/36years, along the Ontario snowbelts of Lake Superior and partially along that of Lake Huron-Georgian Bay at the 95% confidence level during the cold season. Attributions to these negative spatio-temporal trends are explored using data from the North American Regional Reanalysis (NARR) and the Canadian Ice Service (CIS) data sets. Predictor variables show significant warming in lake surface temperature (LST) at a rate of over 6K/36years for Lake Superior, significant decrease in ice cover fraction for both lakes, and an increase in the vertical temperature gradient (VTG) between the LST and the 850mb level. While the behavioural trends of these variables are believed to enhance snowfall through increased evaporation, there are other complex processes involved, such as inefficient moisture recycling and increased moisture storage in warmer air masses that may inhibit the development of snowfall along the immediate leewards shores of Lake Superior.