Soil Moisture Dynamics During Snowmelt

This presentation will discuss the relationship between snowpack meltout and soil moisture dynamics at several SNOTEL sites in Utah and California. Although snowpack meltout is a relatively simple phenomenon to observe, soil moisture changes during meltout are much more difficult to monitor and study. Little research exists that examines soil moisture characteristics under a snowpack, especially during the active meltout period. Since 2005, NRCS’s Salt Lake Snow Survey Staff have been systematically installing soil moisture and temperature sensors at its SNOTEL sites; all sites in Utah, Nevada, and California have soil moisture and temperature sensors at 5 cm, 20 cm, and 50 cm. The analysis of hourly soil moisture, snow water equivalent (SWE), and precipitation data have resulted in the observation of new relationships between daily snowmelt and soil moisture. At most sites, snowpack melt results in diurnal soil moisture fluctuations. At well-drained sites, during periods of rapid melt, fluctuation of up to 10 percent soil moisture by volume are observed. Typically, fluctuations are expressed by all three sensors through the 50 cm measurement zone during the entire meltout period, or until saturation is reached. Diurnal fluctuations in soil moisture typically scale in magnitude with the SWE loss of the previous 24 hrs. Air temperature controls both the magnitude of the melt and the timing of resulting soil moisture cycling. In sites with well-drained soils and no run-in from adjacent areas, the amount of water transmitted through the entire 50cm zone correlates well with the amount of SWE loss on a daily basis. Analysis of diurnal soil moisture fluctuation provides a valuable window into the significant water flux occurring during the melt cycle. Four representative sites with different soil properties and geographic area within Utah and California are examined and the effect of soil properties and site characteristics on throughflow during the melt period is quantified using diurnal soil moisture fluctuation measurements