Modeling Snow–Canopy Processes on an Idealized Mountain

Abstract

Snow interception in a coniferous forest canopy is an important hydrological feature, producing complex mass and energy exchanges with the surrounding atmosphere and the snowpack below. Subcanopy snowpack accumulation and ablation depends on the effects of canopy architecture on meteorological conditions and on interception storage by stems, branches, and needles. Mountain forests are primarily composed of evergreen conifer species that retain their needles throughout the year and hence intercept snow efficiently during winter. Canopy-intercepted snow can melt, fall to the ground, and/or sublimate into the air masses above and within the canopy. To improve the understanding of snow–canopy interception processes and the associated influences on the snowpack below, a series of model experiments using a detailed, physically based snow–canopy and snowpack evolution model [Alpine Multiscale Numerical Distributed Simulation Engine (AMUNDSEN)] driven with observed meteorological forcing was conducted. A cone-shaped idealized mountain covered with a geometrically regular pattern of coniferous forest stands and clearings was constructed. The model was applied for three winter seasons with different snowfall intensities and distributions. Results show the effects of snow–canopy processes and interactions on the pattern of ground snow cover, its duration, and the amount of meltwater release, in addition to showing under what conditions the protective effect of a forest canopy overbalances the reduced accumulation of snow on the ground. The simulations show considerable amounts of canopy-intercepted snowfall can sublimate, leading to reduced snow accumulation beneath the forest canopy. In addition, the canopy produces a shadowing effect beneath the trees that leads to reduced radiative energy reaching the ground, reduced below-canopy snowmelt rates, and increased snow-cover duration relative to nonforested areas. During snow-rich winters, the shadowing effect of the canopy dominates and snow lasts longer inside the forest than in the open, but during winters with little snow, snow sublimation losses dominate and snow lasts longer in the open areas than inside the forest. Because of the strong solar radiation influence on snowmelt rates, the details of these relationships vary for northern and southern radiation exposures and time of year. In early and high winter, the radiation protection effect of shadowing by the canopy is small. If little snow is available, an intermittent melt out of the snow cover inside the forest can occur. In late winter and spring, the shadowing effect becomes more efficient and snowmelt is delayed relative to nonforested areas.

The importance of snowmelt spatiotemporal variability for isotope-based hydrograph separation in a high-elevation catchment

“…Model features include interpolation of meteorological fields from point measurements (Marke, 2008;Strasser, 2008); simulation of shortwave and longwave radiation, including topographic and cloud effects (Corripio, 2003;Greuell et al, 1997); parameterization of snow albedo depending on snow age and temperature (Rohrer, 1991); modeling of forest snow and meteorological processes (Liston and Elder, 2006;Strasser et al, 2011); lateral redistribution of snow due to gravitational- (Gruber, 2007) and wind-induced (Helfricht, 2014;Warscher et al, 2013) processes; and determination of snowmelt using an energy balance approach (Strasser, 2008). Besides having been applied for various other Alpine sites in the past (Hanzer et al, 2014;Marke et al, 2015;Pellicciotti et al, 2005;Strasser, 2008;Strasser et al, 2004Strasser et al, , 2008, AMUND-SEN has recently been set up and extensively validated for the Oetztal Alps region (Hanzer et al, 2016).…”

Effect of meteorological forcing and snow model complexity on hydrological simulations in the Sieber catchment (Harz Mountains, Germany)

“…The model was extended to the fully distributed hydro-climatological model AMUNDSEN (Alpine MUltiscale Numerical Distributed Simulation ENgine, Strasser et al, 2004Strasser et al, , 2008, which includes detailed process descriptions, e.g., for topographydependent radiative transfer, gravitational and windinduced redistribution of snow, technical snow production (Hanzer et al, 2014) and runoff concentration. For both models, a detailed description of snow canopy interaction was added recently (Strasser et al, 2008(Strasser et al, , 2011. This approach includes sub-canopy modifications to open-site meteorological conditions and incorporates a canopy interception model , which builds upon the scaling approach of Pomeroy and Schmidt (1993) and Pomeroy et al (1998).…”

Evaluation of North Eurasian snow-off dates in the ECHAM5.4 atmospheric general circulation model

“…In general, several factors influence the relative timing of snow-off in forests and on open ground (e.g. Essery et al, 2009;Strasser et al, 2011). During the accumulation season, the interception and subsequent sublimation of canopy snow reduces accumulation of snow in forests, while wind-blown snow from open areas may be deposited around forest edges, thus increasing the snow depth.…”