Midwinter Snowmelt Generated by Ground Heat Conduction: Implications for Catchment Hydrology

Ground heat conduction is commonly ignored in modelling of snowpack energy exchanges and snowmelt runoff due to its perceived insignificance relative to other energy sources. Snowmelt at the base of a snowpack was continuously measured during the winter of 2006-2007 with 4 m2 lysimeters at six different sites within a 3.5 km2 continental, mountainous catchment in southeast British Columbia. Soil wetness, soil temperature, and air temperature were also continuously measured at each site. Snowmelt during a three month midwinter period with sub-zero air temperatures ranged from 11 to 113 mm, comprising 3 to 38 % as much as the annual peak snow water accumulation. Given the lack of surface melt, this midwinter snowmelt was driven by ground heat conduction. Spatially, total melt was positively associated with shallow soil moisture content, likely because midwinter snowmelt maintained soil wetness at or near field capacity at three of six sites. There also was likely a positive feedback between soil moisture and melt rate, due to the association between soil thermal conductivity and soil wetness. It is hypothesized that midwinter melt caused by ground heat conduction may be important for enhancing catchment response by maintaining hydrologic connectivity between upslope areas and the channel network.