Influences of temperature and precipitation on historical and future snowpack variability over the Northern Hemisphere in the Second-Generation Canadian Earth System Model

Abstract

e examine the changing roles of temperature and precipitation on snowpack variability in the Northern Hemisphere for Second-Generation Canadian Earth System Model (CanESM2) historical (1850-2005) and future (2006-2100) climate simulations. We show that the strength of the linear relationship between monthly snow water equivalent (SWE) in January?April and precipitation (P) or temperature (T) predictors is a sigmoidal function of the mean temperature over the snow season up to the indicated month. For P-predictors, the strength of this relationship increases for colder snow seasons, whereas for T-predictors it increases for warmer snow seasons. These behaviours are largely explained by the daily temperature percentiles below freezing during the snow accumulation period. We find that there is a threshold temperature (-5±1°C, depending on month in the snow season and largely independent of emission scenario), representing a crossover point below which snow seasons are sufficiently cold that P is the primary driver of snowpack amount, and above which T is the primary driver. This isotherm allows us to delineate the snow-climate regions and elevation zones in which snow cover amounts are more vulnerable to a warming climate. As climate projections indicate that seasonal isotherms shift northward and toward higher elevations, regions where snowpack amount is mainly driven by precipitation recede, whereas temperature-sensitive snow covered areas extend to higher latitudes and/or elevations, with resulting impacts on ecosystems and society.