Abstract
Abstract. We present a new water percolation routine added to the one-dimensional snowpack model Crocus as an alternative to the empirical bucket routine. This routine solves the Richards equation, which describes flow of water through unsaturated porous snow governed by capillary suction, gravity and hydraulic conductivity of the snow layers. We tested the Richards routine on two data sets, one recorded from an automatic weather station over the winter of 2013–2014 at Filefjell, Norway, and the other an idealized synthetic data set. Model results using the Richards routine generally lead to higher water contents in the snow layers. Snow layers often reached a point at which the ice crystals' surface area is completely covered by a thin film of water (the transition between pendular and funicular regimes), at which feedback from the snow metamorphism and compaction routines are expected to be nonlinear. With the synthetic simulation 18 % of snow layers obtained a saturation of > 10 % and 0.57 % of layers reached saturation of > 15 %. The Richards routine had a maximum liquid water content of 173.6 kg m−3 whereas the bucket routine had a maximum of 42.1 kg m−3. We found that wet-snow processes, such as wet-snow metamorphism and wet-snow compaction rates, are not accurately represented at higher water contents. These routines feed back on the Richards routines, which rely heavily on grain size and snow density. The parameter sets for the water retention curve and hydraulic conductivity of snow layers, which are used in the Richards routine, do not represent all the snow types that can be found in a natural snowpack. We show that the new routine has been implemented in the Crocus model, but due to feedback amplification and parameter uncertainties, meaningful applicability is limited. Updating or adapting other routines in Crocus, specifically the snow compaction routine and the grain metamorphism routine, is needed before Crocus can accurately simulate the snowpack using the Richards routine.
Highlights
Knowledge about the process of water percolation in the snowpack is necessary for improving many applications such as flood forecasting, river and reservoir management, slope stability, and avalanche forecasting
The event on 7 March formed a layer with density ∼ 300 kg m−3(at 0.7 to 0.9 m) when run with the Richards routine, which is missing from simulations using the bucket routine
A water percolation routine that solves the Richards equation was added to the Crocus model as a physically based alternative to the empirical bucket routine
Summary
Knowledge about the process of water percolation in the snowpack is necessary for improving many applications such as flood forecasting, river and reservoir management, slope stability, and avalanche forecasting. Measuring liquid water content (LWC) of snow layers is not practical because it is time consuming and LWC has the ability to dramatically change over the timescales that are considerable shorter than those of observations (Techel and Pielmeier, 2011; Wakahama, 1975). Because LWC of a snowpack can change quickly, avalanche forecasters, mountain guides, researchers and rescue workers have reported that they do not fully trust classical snow stability tests (e.g., Rutschblock and extended column tests) when performed in wet-snow (Techel and Pielmeier, 2009). To improve flood and avalanche forecasting capabilities, detailed snowpack hydraulic information on fine spatial and temporal scales is required. One way to achieve a detailed view of snow hydraulics is to supplement
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