Analysis of snowpack dynamics during the spring melt season for a sub‐alpine site using point measurements and numerical modeling

Abstract

Snowpack dynamics through October 2014–June 2017 were described for a forested, sub‐alpine field site in southeastern Wyoming. Point measurements of wetness and density were combined with numerical modeling and continuous time series of snow depth, snow temperature, and snowpack outflow to identify 5 major classes of distinct snowpack conditions. Class (i) is characterized by no snowpack outflow and variable average snowpack temperature and density. Class (ii) is characterized by short durations of liquid water in the upper snowpack, snowpack outflow values of 0.0008–0.005 cm hr−1, an increase in snowpack temperature, and average snow density between 0.25–0.35 g cm−3. Class (iii) is characterized by a partially saturated wetness profile, snowpack outflow values of 0.005–0.25 cm hr−1, snowpack temperature near 0 °C, and average snow density between 0.25–0.40 g cm−3. Class (iv) is characterized by strong diurnal snowpack outflow pattern with values as high as 0.75 cm hr−1, stable snowpack temperature near 0 °C, and stable average snow density between 0.35–0.45 g cm−3. Class (v) occurs intermittently between Classes (ii)–(iv) and displays low snowpack outflow values between 0.0008–0.04 cm hr−1, a slight decrease in temperature relative to the preceding class, and similar densities to the preceding class. Numerical modeling of snowpack properties with SNOWPACK using both the Storage Threshold scheme and Richards' equation was used to quantify the effect of snowpack capillarity on predictions of snowpack outflow and other snowpack properties. Results indicate that both simulations are able to predict snow depth, snow temperature, and snow density reasonably well with little difference between the 2 water transport schemes. Richards' equation more accurately simulates the timing of snowpack outflow over the Storage Threshold scheme, especially early in the melt season and at diurnal timescales.

Hydrogeophysical Inversion of Time‐Lapse ERT Data to Determine Hillslope Subsurface Hydraulic Properties

“…Cumulative potential evapotranspiration for the 2018 water year was 66 cm. Winter snowmelt rates were determined from two snowmelt lysimeters installed at the hillslope (Pleasants et al., 2017) while summer rain events were measured with a Texas Electronics, Inc. TE‐525WS tipping bucket rain gauge. Cumulative snowmelt collected by the lysimeters during the 2017–2018 winter was 46 cm.…”

“…Watershed vegetation is composed mainly of engelmann spruce, subalpine fir, and lodgepole pine. The snow season typically lasts from mid‐October to early June and the snowmelt period from mid‐March to early June (Pleasants et al., 2017).…”

“…Driving data were applied to the model using daily values. Potential evapotranspiration was split into potential evaporation and transpiration using Equations and with $$LAI=\,$$ 5 m 2 m −2 , which is representative of environments in the Rocky Mountains, USA (Binkley et al., 2003; Pleasants et al., 2017). A 5‐year spin‐up period was used to allow model predictions to reach dynamic‐equilibrium between simulation years and minimize the influence of the initial pressure heads on the final simulation results.…”

Technical note: Snow Water Equivalence Estimation (SWEE) Algorithm from Snow Depth Time Series Using a Snow Density Model

“…The site was instrumented with a snow lysimeter, ranging snow depth sensor, and snow surface temperature, but there is no snow pillow at the NN Creek research site. More detailed information regarding this site is available in Pleasants et al (2017), Thayer et al (2018), andHe et al (2018). Figure 3 shows the computed SWE change ∆ during the snowmelt season of 2018, which includes the lysimetric snowmelt water flux at the bottom of snowpack, denoted in the blue-shaded area.…”

Measured and modelled above‐ and below‐canopy turbulent fluxes for a snow‐dominated mountain forest using GEOtop

“…The annual water balance is snow dominated with estimated mean annual air temperature of 1.7°C and estimated mean annual precipitation of 1,160 mm. The slope (length = 75 m; aspect = 180°; angle = 22°) is generally snow covered from November to May (Pleasants, Kelleners, & Ohara, ).…”