Snow distribution dynamics under forest canopy

Snow in a subalpine forest

Radiation measurements below canopy

Background

Snow accumulation and ablation within forest structures demonstrates much greater heterogeneity as compared to snow falling within open or alpine areas. The forest canopy can act to exacerbate and diminish physical forcing through radiation absorption and dispersion, turbulent flux zonation as well as precipitation interception. Heterogenous canopy structures can complicate precision estimates of snow cover due to the highly complex spatio-temporal dynamics of accumulation and melting snow. Depending on the overlying structure, both maximum and minimum snow melt rates can be found under the canopy in relation to surrounding open areas. Boreal and subalpine forests cover large land areas within the northern hemisphere. In Switzerland, forest cover encompasses approximately 30% of country with much this area housing seasonal snow cover.

Approach / Measurements

Snow distribution: A variety of measurement schemes have been integrated into this study in efforts to augment manual snow depth and snow water equivalence measurements. Ground penetrating radar (GPR) is being utilized to provide continuous snow cover information. GPR output of snow characteristics is a major improvement over traditional point based measurement methods. Terrestrial laser scans (TLS) of the forest will provide us with high resolution representations of the surrounding canopy and vegetation characteristics as well as detailed information regarding local snow depth distribution.

Energy balance: We focus on the radiation transfer into subalpine forests. A novel instrument was developed to capture the spatio-temporal variability of shortwave and longwave radiation within the canopy: An automated four-component net-radiometer is constantly moved back and forth along a 10-m transect. As reference, two fixed net-radiometer are installed, one instrument above the canopy and another instrument on a nearby clear-cut site.

Sites

Most of the field work takes place at field sites surrounding Davos. The radiation measurements are carried out on two long-term research sites. Between 2003 and 2007 the automated net-radiometer was installed at our research site in Alptal at 1200 m a.s.l. Since then the radiation measurements are being continued at our research site Seehornwald in Davos at 1650 m a.s.l.

Link to other projects

This project is important to increase our monitoring and forecasting ability of snow water resources in forested terrain (see operational snow-hydrological service). The project also contributes to the development of our snowcover models, Snowpack and Alpine3D. These models include a detailed representation of snow-forest processes and have been tested against field data from this project (SnowMIP2).

Project team

• David Moeser
• Tobias Jonas
• Manfred Stähli
• David Gustafsson

Students / trainees

• Nena Griessinger (2010/11)
• Aline Andrey und Pascal Spiess (2009/10)
• Martine Broer (2008/09)
• Raphael Hubacher (2007/08)
  
• Marco Hardmeier (2005/06)

Contact

• Tobias Jonas