The influence of lateral snow redistribution processes on snow melt and sublimation in alpine regions
Highlights
► Modeling of the combined processes of wind induced and gravitational snow transport. ► The maximum sublimation rate is heavily reduced by gravitational snow transport. ► Analysis of 2D and 3D model results at different scales. ► 2D and 3D results becoming similar from a certain scale on.
Introduction
The presented study is focused on defining an adequate model to represent snow patterns formed by the accumulation and ablation dynamics of the snow cover as well as by lateral snow transport processes and on the effect of these patterns on calculated sublimation from snow in turbulent suspension. Furthermore, a scaling study is realised with respect to the calculated snow melt rates. The scaling study is focused on the question whether blowing snow processes which are mentioned as the dominant factor, which is influencing the snow distribution at scales from tens to hundreds of meters (Liston, 2004) and gravitational snow transport which can modify the snow distribution at tens of meters (Bernhardt and Schulz, 2010) can impact the predicted melt rates over the same order of scales. The necessary model runs were accomplished by applying an established snow evolution model (SnowModel; Liston and Elder, 2006a), that includes model routines for the description of snow accumulation and ablation as well as wind induced snow transport, to the German Alpine catchment Berchtesgaden National Park (BNP).
Sublimation from suspended particles as firstly mentioned by Dyunin (1967) is a moisture flux from the snow particle to the surrounding undersaturated atmosphere. The intensity of the sublimation process depends of the availability of transportable snow, on the wind speed and on the air humidity (Hood et al., 1999). Sublimation rates were firstly quantified by Schmidt, 1972, Lee, 1975 and later on estimated through model calculations (Dery and Yau, 2001, MacDonald et al., 2010; Pomeroy, 1991; Schmidt, 1982, Strasser et al., 2008). A literature review showed that the calculated seasonal rates of sublimations do have a very high range, reaching values from 4 mm within 6 months at a snow covered Antarctic ice shelf site (King et al., 1996), to 37–85 mm within a snow season at a Canadian tundra site (Essery et al., 1999, Pomeroy, 1997), to 135 mm in 5 month in the Colorado front range (Meiman and Grant, 1974), up to 1265 mm within a snow season at an Alpine ridge (Strasser et al., 2008). Given this uncertainty, it is of importance to know if the model results indicate that sublimation has a significant impact on the water balance of a whole catchment, or if the sublimation effect is only of local importance. Within the presented work, the results of Strasser et al. (2008) were extended by the inclusion of gravitational snow transport processes. This is needed, because gravitational transport removes snow from crests and steep walls which do usually show enhanced wind speeds and accumulates snow at the foothills and wind sheltered areas. The effect of this transport process on the calculated sublimation rates is discussed and the results are compared to established results of Dery and Yau (2001). Furthermore, given the current computational constraints for describing snow hydrological processes within complex, coarse-scale hydrological and climate models, it is of great interest to analyse and define which processes, what type of model complexity, and which process interactions are required to be represented at the scales associated with each application (Bloschl, 1999). The Snow Models Intercomparison Project (SnowMIP) (Etchevers et al., 2004) showed that present-day 1-dimensional snow models are able to reproduce the snow cover evolution if they are applied in close vicinity of a meteorological station. Results become less confident for spatially distributed 2- or 3-dimensional models (see Fig. 1), especially in areas with complex terrain or in forested areas (Bernhardt and Schulz, 2010, Bernhardt et al., 2009, Liston, 2004, Liston and Elder, 2006a, Pomeroy et al., 2002, Rutter et al., 2009). This can be attributed to errors and uncertainties in the calculated meteorological fields which drive the models, as well as to oversimplifications of the model formulations with respect to snow–canopy interactions, windblown snow, gravitational snow transport, and preferential snow deposition (Bernhardt et al., 2009, Gruber, 2007, Lehning et al., 2006, Liston, 2004).
Hence, the predicted melt water generation is analysed with the help of two different model set-ups and at different scales for analysing for which scales and which model resolution the calculation of lateral snow transport processes is needed.
Section snippets
Study area and data
Berchtesgaden National Park (BNP) is located in south-eastern Germany, in the Free State of Bavaria (Fig. 2) and comprises an area of approximately 208 km2. The montane to high Alpine area of BNP includes the massifs Watzmann (2713 m a.s.l.) and Hochkalter (2606 m a.s.l.) and parts of the massifs Hoher Göll, Hagengebirge, Steinernes Meer, and Reiter Alm, which are situated along the national boundary between Germany and Austria. These massifs are separated by deep valleys characterised by
Model description
SnowModel (Liston and Elder, 2006a) was used to simulate BNP’s snow distribution. SnowModel in the presented version is a modular model and consists of five modules: (i) MicroMet interpolates the meteorological station data (Liston and Elder, 2006b), (ii) EnBal estimates the energy balance at Earth’s surface, (iii) SnowPack calculates the snowpack energy balance, (iv) SnowTran-3D calculates wind induced snow transport (Liston et al., 2007) and (v) SnowSlide approximates the effects of
Results and discussion
In the following, two different model setups are used for the simulations and sensitivity studies. The first setup simulates the accumulation and ablation of snow, but omits horizontal transport processes (defined as 2D). The second setup includes the processes simulated in the 2D setup, with the addition of horizontal transport by wind and gravity (defined as 3D).
Conclusion
The effect of different snow distribution and redistribution processes in complex, Alpine terrain was analysed to determine their relative contributions to observed snow patterns. In addition, sublimation and snow melt rates for the Berchtesgaden National Park catchment were examined. Snow melt rates, as a potential important component of catchment runoff during spring and summer periods, were also analysed on different spatial scales. It has been shown that increasing the model complexity by
Acknowledgements
The authors wish to thank the administration of the Berchtesgaden National Park for providing the GIS data; the rangers of the National Park for their assistance in the field; and the Bavarian Avalanche Warning Service for providing meteorological data. We also thank B. Mehdi for skilfully proof reading an early version of the manuscript.
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