ALPINE-3D

Alpine3D is a spatially distributed (surface), three dimensional (atmospheric) model for analyzing and predicting dynamics of snow-dominated surface processes in mountainous topography. It includes models for snow cover, vegetation and soil, snow transport, radiation transfer and runoff which can be enabled or disabled on demand.

The model supports a variety of input options including interpolation of meteorological weather stations, input from a meteorological model or from remote sensing data (MeteoIO) and has been parallelized in order to run on computing grids or clusters.

MeteoIO:

In order to accommodate the diversity of meteorological data sources (local files, remote database, web services, output of other models or forecast) as well as carry out the necessary preparation of the data, a standalone library, MeteoIO, has been created. This library offers a plugin infrastructure for data access, data filtering and resampling as well as spatial interpolations. It has been designed to work transparently and unattended.

Figure 1: The Alpine 3D modular structure

Snow drift module

Drifting and blowing snow is an impressive phenomenon of snow covered surfaces. In the mountains, snow deposition and snow transport is dominated by the interaction of the local terrain with the wind. These interactions are investigated using a combination of wind field (Raderschall et al., 2008) and snow transport simulations (Lehning et al., 2008). A special focus of the research work is to investigate the preferential deposition of precipitation as a function of the flow field and the scale-dependent transport processes suspension and saltation. The overall goal is to physically explain the very heterogeneous snow cover properties in complex terrain. The model system has been applied to explain the mass balance of accumulation dominated glaciers (Mott et al., 2008; Dadic et al., 2009).

Energy balance module

The radiation balance in mountainous regions is significantly influenced by topographic effects at scales which cover individual mountains to slopes and even down to trees. Shortwave incoming radiation is altered by shading, reflection and multiple reflections. Longwave radiation from the sky is altered by longwave irradiance emitted by surrounding terrain. As the topography becomes steeper and local influences play a more important role these effects become more pronounced. The implementation of the radiosity approach (Helbig et al., 2009) in combination with distributed information on surface properties (e.g. vegetation, soil, snow) allows the consideration of the different radiative exchanges.

Figure 2: Modelled shortwave incoming radiation for the 5th of March at midday. Terrain influences on the radiation are clearly visible. Whereas north facing slopes receive hardly any shortwave radiation (shown in blue), south facing slopes receive values up to 1300 W/m² (shown in red).

SNOWPACK module

On every Alpine3D grid cell, a complete SNOWPACK simulation is made, allowing multi-layer soil–snow–vegetation representation. The strength of Alpine3D is the detailed representation of surface heterogeneity especially in snow-covered terrain.

Figure 3: comparison of measured and simulated snow depth at a pixel equipped with an automatic weather station. No feed back from the measured snow height is used for such simulation, the model only relies on purely meteorological parameters.

Runoff module 

Runoff from the vegetation–snow/ice–soil columns in each Alpine3D grid cell is collected in a series of linear reservoirs to simulate sub-surface routing. This is a simple scheme to produce catchment runoff predictions from the surface forcing. The quantitative influence of vegetation representation and terrain-modified radiation together with a first complete description of Alpine3D is available from Lehning et al. (2006).

Application examples

Alpine3D has a broad variety of potential applications. Most dominant is the assessment of snow water resource dynamics in mountain catchments (Michlmayr et al., 2008). This includes predictions of future snow on the basis of climate change scenarios (Bavay et al., 2009). One exotic application of the model system Alpine3D is the forecasting of surface temperatures on ski-pistes, e.g. for the Vancouver winter olympics. For this forecast local shadings (might) change surface temperature up to 5 °C.

Figure 4: Snow Water Equivalent distribution in the Dischma (Switzerland) catchment.

Input data requirements:

As information about the topography and surface characteristics a digital elevation model and a grid of land use classes must be provided in addition to the meteorological input described above. Soil characteristics have to be specified in terms of one dimensional soil profile of physical parameters such as height, porosity, thermal conductivity etc for individual layers.