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Estimation of Winter Leaf Area Index and Sky View Fraction for Snow Modelling in Boreal Coniferous Forests
University of Helsinki.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Physics.
Finnish Forest Research Institute.
Finnish Forest REsearch Institute.
2008 (English)Conference paper, Abstract (Other academic)
Abstract [en]

Leaf area index (LAI) and sky view fraction have an important role in controlling snow interception capacity, throughfall fraction, and canopy radiation transfer in snow energy balance models developed for forest conditions. In most models winter LAI and sky view fraction are provided by the user a priori as model parameters. Because stems, branches and needles are capable of intercepting water, snow and radiation, LAI needs to be defined in terms of the total plant area. Plant area indices (PAI) or winter 'effective' LAI values have been introduced in the snow models. Canopy parameters are typically adopted from literature, where the relationship between the winter LAI and sky view fraction is described with different mathematical functions. Winter LAI and sky view fraction can be measured using optical methods. Optical measurements include radiation transmission observations by plant canopy analysers or analysis of hemispheric photographs. Measurements of tree biomass provide another option for the determination of LAI. Computation of LAI from the biomass is a tempting option, because an estimate of stand biomass can easily be derived from operational forest inventory data. The first objective of this study was to estimate winter LAI and sky view fraction using different methods. Optical and biomass-based approximations of winter LAI and sky view fraction were available from coniferous forests in Scandinavia with different stand density and site latitude. The biomass-based estimate of LAI was found to be comparable with the values derived from the optical measurements in most sites. Heterogeneity of tree species and site fertility, as well as edge effects between different forest compartments caused differences in the LAI estimates in some sites. The second goal was to apply a snow energy balance model (SNOWPACK) to detect, how the differences in the estimated values of the winter LAI and sky view fraction are reflected in simulated snow processes. An increase in LAI and a decrease in the sky view fraction changed the snow surface energy balance by decreasing short-wave radiation input and increasing long wave radiation input. Changes in the studied canopy parameters had a direct impact on snow accumulation through altered throughfall fraction, and an indirect and less visible impact on snowmelt through the changed surface energy balance.

Place, publisher, year, edition, pages
National Category
Oceanography, Hydrology, Water Resources
URN: urn:nbn:se:kth:diva-88861OAI: diva2:502507
American Geophysical Union (AGU), Fall meeting 2008. San Francisco, CA, USA. 15-19 December 2008
Abstract #C34A-01. QC 20120510Available from: 2012-02-14 Created: 2012-02-14 Last updated: 2012-05-10Bibliographically approved

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