Linking global changes of snowfall and wet-bulb temperature

Snowfall is one of the primary drivers of the global cryosphere and is declining in many regions of the world with widespread hydrological and ecological consequences. Previous studies have shown that the probability of snowfall occurrence is well described by wet-bulb temperatures below 1 degrees C (1.1 degrees C) over land (ocean). Using this relationship, wet-bulb temperatures from three reanalysis products as well as multisatellite and reanalysis precipitation data are analyzed from 1979 to 2017 to study changes in potential snowfall areas, snowfall-to-rainfall transition latitude, snowfall amount, and snowfall-to-precipitation ratio (SPR). Results are presented at hemispheric scales, as well as for three Koppen-Geiger climate classes and four major mountainous regions including the Alps, the western United States, High Mountain Asia (HMA), and the Andes. In all reanalysis products, while changes in the wet-bulb temperature over the Southern Hemisphere are mostly insignificant, significant positive trends are observed over the Northern Hemisphere (NH). Significant reductions are observed in annual-mean potential snowfall areas over NH land (ocean) by 0.52 (0.34) million km(2) decade(-1) due to an increase of 0.34 degrees C (0.35 degrees C) decade(-1) in wet-bulb temperature. The fastest retreat in NH transition latitudes is observed over Europe and central Asia at 0.7 degrees and 0.45 degrees decade(-1). Among mountainous regions, the largest decline in potential snowfall areas is observed over the Alps at 3.64% decade(-1) followed by the western United States at 2.81% and HMA at 1.85% decade(-1). This maximum decrease over the Alps is associated with significant reductions in annual snowfall of 20 mm decade(-1) and SPR of 2% decade(-1).