Measuring and Modelling the Snow Distribution on Wannengrat, Davos

Investigating the spatial and temporal variability of the alpine snowpace is vital for the assessment of avalanche danger as well as the calculation of hydrological resources in an alpine watershed.

This variability of the snowpack is governed by snow drift through wind and by the localised energy balance of the snow surface. The driving force in snow transport is the boundary layer (surface) wind field, whose flow is modified in both speed and direction by the complex topography of the underlying surface. The resulting variations in the wind field cause the inhomogeneous deposition of precipitation on the landscape.

In order to improve understanding of the spatial variability of the snowpack, it is necessary to measure snow height at high spatial resolution as well as to measure the prevailing meteorological conditions.

It is for this reason that SLF set up the Wannengrat research site, where wind, temperature and solar radiation are measured on seven permanent automatic meteorological stations and min. 19 mobile SensorScope stations (provided by SwissEx during winter 2009/10). These meteorological data are required for the initialisation and validation of numerical models. In addition to the measurements above, LIDAR provides measurements of snow height and the spatial deposition of the snow in the research area and will eventually enable definition of the recurring snow deposition patterns.

Following field measurements, the driving processes leading to the variability of the snowpack may identified and quantified with the help of numerical model calculations. For this, the localised windfields and snow drift are calculated at a high spatial resolution of only a few meters.

The atmospheric model ARPS (Advanced Regional Prediction System, Center for Analysis and Prediction of Storms - University of Oklahoma) is used for the calculation of the flow field. With this model, simulations can be carried out on a number of different scales and the calculated flow fields are used as a 3-Dimensional input to the physical surface process model ALPINE3D. Within ALPINE3D, the spatial snow redistribution in the research area can then be simulated for a variety of drift periods. In order to do this, the various drift processes (saltation, suspension and preferential deposition) of snow and the localised energy balance of the snow surface must all be modelled and then verified based on the LIDAR measured deposition.

• Rebecca Mott