Verification of the multi-layer SNOWPACK model with different water transport schemes

Abstract

Abstract. The widely used detailed SNOWPACK model has undergone constant development over the years. A notable recent extension is the introduction of a Richards equation (RE) solver as an alternative for the bucket-type approach for describing water transport in the snow and soil layers. In addition, continuous updates of snow settling and new snow density parameterizations have changed model behavior. This study presents a detailed evaluation of model performance against a comprehensive multiyear data set from Weissfluhjoch near Davos, Switzerland. The data set is collected by automatic meteorological and snowpack measurements and manual snow profiles. During the main winter season, snow height (RMSE: < 4.2 cm), snow water equivalent (SWE, RMSE: < 40 mm w.e.), snow temperature distributions (typical deviation with measurements: < 1.0 °C) and snow density (typical deviation with observations: < 50 kg m−3) as well as their temporal evolution are well simulated in the model and the influence of the two water transport schemes is small. The RE approach reproduces internal differences over capillary barriers but fails to predict enough grain growth since the growth routines have been calibrated using the bucket scheme in the original SNOWPACK model. However, the agreement in both density and grain size is sufficient to parameterize the hydraulic properties successfully. In the melt season, a pronounced underestimation of typically 200 mm w.e. in SWE is found. The discrepancies between the simulations and the field data are generally larger than the differences between the two water transport schemes. Nevertheless, the detailed comparison of the internal snowpack structure shows that the timing of internal temperature and water dynamics is adequately and better represented with the new RE approach when compared to the conventional bucket scheme. On the contrary, the progress of the meltwater front in the snowpack as detected by radar and the temporal evolution of the vertical distribution of melt forms in manually observed snow profiles do not support this conclusion. This discrepancy suggests that the implementation of RE partly mimics preferential flow effects.

Snow farming: conserving snow over the summer season

“…The multilayer model includes a detailed description of the energy and mass fluxes within the snow and between snow, atmosphere and soil (e.g. Lehning et al, 2002a, b;Wever et al, 2015). For this publication SNOWPACK was applied to simulate the evolution of the two snow heaps during a complete summer season.…”

Simulating the influence of snow surface processes on soil moisture dynamics and streamflow generation in an alpine catchment

“…This is explained by the fact that this particular site is relatively sensitive to wind eroding snow from the surface. The snow depth in the snow season of 2012 is overestimated at all stations, which is related to unusual meteorological circumstances of large snowfall accompanied by strong winds, which lead to an overestimation of precipitation as measured by the heated rain gauge (also discussed in Wever et al, 2015). Nevertheless, the snow cover development at those three sites is overall satisfactorily simulated in Alpine3D for providing an upper boundary for the soil.…”

“…The rocky surface pixels were initialised uniformly with loamy sand. This is based on observations when installing soil temperature sensors at the WFJ, which is located in the rock class and for which plausible simulations were obtained using this soil class (Wever et al, 2015). All other pixels (65 %), including forests, meadows, pasture, bare soil and occasional pixels that are defined as agricultural use were initialised using an upper layer of 60 cm consisting of silt loam and a lower layer of 240 cm consisting of sandy loam.…”

“…In snow-free conditions, the upper boundary condition is defined by rainfall; evaporation and deposition result from the latent heat flux. Phase changes in soil are calculated following Wever et al (2015). Water retention curves in the SNOWPACK model are based on the van Genuchten model (van Genuchten, 1980) via predefined soil types as in the ROSETTA class average parameters (Schaap et al, 2001).…”

“…In alpine terrain, considering the length scales less than a few 100 m is important as on these scales, wind drifts determine the snow accumulation and local topography heavily influences the energy balance via the slope aspect, angle and local shading. In this study, the recent addition to the SNOWPACK model of a solver for Richards Equation for soil (see Wever et al, 2014aWever et al, , 2015 is verified against soil moisture measurements in the vicinity of Davos, Switzerland. The SNOW-PACK model provides the surface scheme in the Alpine3D model framework, using physics-based descriptions of soilsnow-vegetation processes (Gouttevin et al, 2015).…”