Snowmelt energetics at a shrub tundra site in the western Canadian Arctic

Abstract

Abstract:Snow accumulation and melt were observed at shrub tundra and tundra sites in the western Canadian Arctic. End of winter snow water equivalent (SWE) was higher at the shrub tundra site than the tundra site, but lower than total winter snowfall because snow was removed by blowing snow, and a component was also lost to sublimation. Removal of snow from the shrub site was larger than expected because the shrubs were bent over and covered by snow during much of the winter. Although SWE was higher at the shrub site, the snow disappeared at a similar time at both sites, suggesting enhanced melt at the shrub site. The Canadian Land Surface Scheme (CLASS) was used to explore the processes controlling this enhanced melt. The spring-up of the shrubs during melt had a large effect on snowmelt energetics, with similar turbulent fluxes and radiation above the canopy at both sites before shrub emergence and after the snowmelt. However, when the shrubs were emerging, conditions were considerably different at the two sites. Above the shrub canopy, outgoing shortwave radiation was reduced, outgoing longwave radiation was increased, sensible heat flux was increased and latent flux was similar to that at the tundra site. Above the snow surface at this site, incoming shortwave radiation was reduced, incoming longwave radiation was increased and sensible heat flux was decreased. These differences were caused by the lower albedo of the shrubs, shading of the snow, increased longwave emission by the shrub stems and decreased wind speed below the shrub canopy. The overall result was increased snowmelt at the shrub site. Although this article details the impact of shrubs on snow accumulation and melt, and energy exchanges, additional research is required to consider the effect of shrub proliferation on both regional hydrology and climate.

Modelled sensitivity of the snow regime to topography, shrub fraction and shrub height

“…Ground-based measurements, remote sensing and modelling studies in the Yukon Bewley et al, 2010), the Northwest Territories (Marsh et al, 2010), Alaska (Sturm et al, 2005a), Fennoscandia (Cohen et al, 2013) and the pan-Arctic (Loranty et al, 2011) have all shown that shrub branches exposed above snow decrease the surface albedo and increase the absorption of solar radiation. Shrubs can even absorb radiation while buried because short-wave radiation penetrates snow (Warren, 1982;Baker et al, 1991;Hardy et al, 1998).…”

“…Tall shrubs reduce the short-wave radiation reaching the snow surface by shading but increased long-wave radiation and sensible heat fluxes from the canopy to the snow can give higher melt rates for snow beneath shrubs than for unshaded snow (Bewley et al, 2010). For example, Sturm et al (2005b), Pomeroy et al (2006) and Marsh et al (2010) observed higher melt rates where shrubs were exposed above the snowpack than where shrubs were buried.…”

“…Bewley et al, 2007Bewley et al, , 2010Marsh et al, 2010;Ménard et al, 2012). However, one of the remaining difficulties in modelling shrub-tundra is how to represent sparse canopies and horizontal interactions between shrub and non-shrub surfaces.…”

Changes in the understory plant community and ecosystem properties along a shrub density gradient

“…Shrub-bryophyte interactions modify these controls, where declines in bryophyte cover under dense shrub canopies have been found to increase ground heat flux partitioning, despite increases in soil evaporation, resulting in warmer summer soil temperatures (Blok et al 2011b), which would increase litter decomposition. In contrast, it has been suggested that shading by shrub canopies may decrease summer soil temperatures (Marsh et al 2010), which in turn may decrease decomposition rates. Moreover, changes in soil moisture regimes will affect decomposition with predicted increased evapotranspiration rates under shrubs drying soils (Chapin et al 2000) and potentially leading to microbial moisture limitations.…”

Land cover classification in multispectral imagery using clustering of sparse approximations over learned feature dictionaries

“…[6][7][8][9] Colonizing shrubs affect snowpack depth, although it is yet unclear at what magnitude and in what direction. 5 Recent studies have attributed dramatic increases in the rates of shoreline erosion along Arctic coastlines and riverbanks to global climate change and near-surface permafrost degradation. 13,14 Across much of the Arctic, the number of lakes and their sizes have also been changing as a result of permafrost degradation, 15 altering surface water dynamics and causing possible release of soil organic carbon.…”