Sources of variability in winter soil temperature moderation by mountain snowpacks

The insulation provided by seasonal snowpacks is an important controller of temperature in mountain soils, but the significance of this effect across the landscape is not well understood. We analyzed recent records of snowpack and soil temperature from the NRCS SNOTEL network, a network of automated snow monitoring stations in the Rocky Mountains, to determine seasonal and topographic patterns in soil temperature, and their relationship to mountain snowpacks. These stations range in elevation between 1700m to almost 3500m and receive a mean peak snow water equivalent between 200 and 1200mm. Among these sites, we found that mean January soil temperatures are several degrees warmer than mean air temperatures, and winter soil temperatures decline more slowly with elevation than air temperature lapse rates. Middle-elevation soils (2250-2750m) tend to remain warmer throughout the winter than soils at higher or lower elevations. At individual sites, a late onset of persistent snowcover was associated with soil freezing events in the fall, and lower soil temperatures during the early portion of the winter. At all sites, January soil temperatures at 5cm depth average between -2°C and 1.5° C, a temperature range at which below-snow organisms have shown great sensitivity. This analysis suggests that the moderating effect of seasonal snowpacks on winter soil temperatures varies significantly with elevation and across inter-annual timescales. This may have important implications for ecosystem processes that take place below the snowpack.