Quantifying the Impacts of a Needleleaf Canopy on the Physical Properties of the Snowpack at the Local Scale
Abstract
Heterogeneous needleleaf forests alter the incoming solar radiation, emit infrared radiation, partly intercept precipitation and lower the near-surface wind speed. This creates strong temporal and spatial variability of snow on ground at the local scale during winter. While the forest's impacts on snow depth and water equivalent are fairly well documented, gaps in our knowledge of the more detailed physical properties of the snowpack (stratigraphy, thermal regime, etc.) persist. This study aims to contrast the large variability of these properties between a small forest gap (approx. 1.5H) and underneath a closed canopy (LAI = 5.5), in a humid boreal forest located in southeastern Canada (47.3°N, 71.2°W). Snow depth was assessed automatically at both sites during winter 2018-19. A vertical array of needle probes also measured temperature and effective thermal conductivity (keff) of snow underneath the canopy. A total of 52 snow pits measurements were made at weekly intervals during the full extent of the snow season, which allowed to have a detailed monitoring of the snowpack physical properties and SWE. The study area received more than 900 mm of precipitation during the snow cover period, for a maximum snow depth measured inside the forest opening of 195 cm and a peak SWE of 800 mm, versus 155 cm and 650 mm underneath the canopy. This shallower snowpack below the canopy along with cold temperatures enhanced the vertical vapor fluxes in the early season, intensifying facetisation of the grains. Unloading of water from the branches after winter rainfalls fosters the formation of thick ice crusts generating an increase of keff up to 0.3 Wm-1K-1 for the remaining of winter. From this intensive field campaign, it is assumed that a reduced snow depth underneath the canopy, induce stronger heat and vapor vertical transfers through the snowpack which accelerate the metamorphism of the grains. Results show that specific surface area is 5 m2kg-1 more inside forest gaps in general for any given date compared to what is observed below the canopy where more faceted grains and less compaction load also create a snowpack with a lower density.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C33D1611B
- Keywords:
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- 0736 Snow;
- CRYOSPHERE;
- 0758 Remote sensing;
- CRYOSPHERE;
- 0794 Instruments and techniques;
- CRYOSPHERE;
- 0798 Modeling;
- CRYOSPHERE