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United States Department of Agriculture

Agricultural Research Service

Title: Small-scale spatial variability of sub-canopy radiant energy during snowmelt in decidous and confierous forest patches

Authors
item Link, Timothy - UNIV OF IDAHO
item Reba, Michele - UNIV OF IDAHO
item Essery, Richard - UNIV OF WALES
item Hardy, Janet - USACE/CRREL
item Marks, Daniel
item Pomeroy, John - UNIV OF SASKATCHEWAN

Submitted to: Trans American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: November 7, 2005
Publication Date: December 15, 2005
Citation: Link, T.E., Reba, M.L., Essery, R.L., Hardy, J.P., Marks, D., and Pomeroy, J.W. 2005. Small-scale spatial variability of sub-canopy radiant energy during snowmelt in deciduous and coniferous forest patches, abstract C21A-1073, Eos, Transactions of the American Geophysical Union, 86(52): F432

Technical Abstract: In mountainous, forested environments, snowcover dynamics exert a strong control on hydrologic and atmospheric processes. Snowcover ablation patterns in forests are controlled by a complex combination of depositional patterns coupled with radiative and turbulent heat flux patterns related to topographic and canopy cover variations. Quantification of small-scale variations of radiant energy in forested environments is necessary to understand how canopy structure affects snowcover energetics to improve spatially-explicit physically-based snowmelt models. Incoming solar and thermal radiation patterns were measured during the melt season around individual trees in isolated deciduous and coniferous forest patches. During clear to partly cloudy conditions, solar radiation around the leafless deciduous tree was reduced by 68%, whereas thermal radiation was enhanced by 26%. Under similar meteorological conditions, solar radiation was reduced by 87% and thermal radiation was enhanced by 43% beneath the crown of the coniferous tree. To assess potential impacts of radiative differences between open and sub-canopy net snowcover radiation, a simple analysis of sensitivity of net snowcover radiation to a range of snowcover albedo values was completed. For the meteorological conditions during this study, the analysis indicates that the deciduous canopy is likely to have a minor impact on net radiation differences. The area beneath the coniferous crown is expected to exhibit enhanced net radiation for relatively high (> 0.6) open site albedo values. A small forest gap is expected to exhibit minimal difference relative to open sites for typical albedo values, whereas a large gap is expected to exhibit less net radiation than open areas. During cloudy to overcast conditions, net radiation at all canopy locations is expected to be lower than at open sites. These net radiation differences coupled with decreased turbulent fluxes due to lower wind velocities and reduced snow water equivalent values due to canopy interception losses help to explain small-scale patterns of snowmelt in non-uniform forested areas. This work also emphasizes the need to consider canopy heating in sparse forest and edge environments and to develop an improved understanding of sub-canopy snowcover albedo patterns and dynamics.

Last Modified: 8/27/2014
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