A climatology of snowfall-temperature relationships in Canada

A better understanding of potential climate change impacts on the global hy drological cycle requires knowledge of the interaction between air temperat ure and water in its various farms. One important example is the effect of air temperature on snowfall. Proper parameterization of the snowfall-temper ature relationship in climate models is essential for accurate prediction o f future snowfall changes that might arise from high-latitude warming. On a climatological basis, at any location, air temperature and snowfall can be correlated positively (higher temperatures increase atmospheric moisture a nd snowfall through the Clausius-Clapeyron relationship) or negatively (pre cipitation falls as rain instead of snow). Examination of 50 years of month ly snowfall water equivalent and mean temperature data indicates that the s nowfall-temperature relationship is positive in the high latitudes and nega tive in southern Canada, along both coasts, and east of the Rockies. The "z ero line" (the transition zone north of which warmer months receive more sn owfall than colder months) migrates southward from autumn to winter so that by January most of eastern and northwestern Canada has a positive snowfall -temperature slope. The primary exception to a straightforward relationship between slope and latitude occurs east of the Rockies, where anomalous neg ative slopes extend far to the north. In this region, dry, adiabatically wa rmed air from downslope or circulation effects may reduce the number of sno w events and modify the slope of the snowfall-temperature curve. Based on f irst principles and Canadian observations, we develop a function relating t emperature to snowfall that attempts to account for the complex spatial and seasonal nature of the snowfall-temperature relationship. Given the import ance of snowfall in the global radiation balance, this analysis could be us ed to improve climate change predictions.