Controls on Spatial and Temporal Variability in Northern Hemisphere Terrestrial Snow Melt Timing, 1979–2012

Abstract

pring snowmelt onset has occurred earlier across much of the Northern Hemisphere land area in the last four decades. Understanding the mechanisms driving spring melt has remained a challenge, particularly in its spatial and temporal variability. Here, melt onset dates (MOD) obtained from passive microwave satellite data are used, as well as energy balance and meteorological fields from NASA?s Modern-Era Retrospective Analysis for Research and Applications, to assess trends in the MOD and attribute melt onset across much of Arctic and sub-Arctic Eurasia and North America during the spring snowmelt season from 1979 to 2012. Across much of the Northern Hemisphere MOD has occurred 1?2 weeks earlier over this period, with the strongest trends in western and central Russia and insignificant trends across most of North America. Trends in MOD are reflected by those in energy balance terms, with energy advection providing an increasing proportion of melt energy in regions with the strongest MOD trends. Energy advection plays a larger role in melt onset in regions where snow begins melting in March and April, while insolation and longwave radiation drives melt where the MOD occurs in May and June. This implies that there is a potential shift in snowmelt drivers toward those involved in advective processes rather than radiative processes with an earlier MOD. As the high latitudes warm and terrestrial snow cover continues to melt and disappear earlier in the spring, it is valuable to elucidate regional snowmelt sensitivities to better understand regional responses to changing climatological processes.