Estimation of winter leaf area index and sky view fraction for snow modelling in boreal coniferous forests: consequences on snow mass and energy balance |
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| Authors: | Sirpa Rasmus David Gustafsson Harri Koivusalo Ari Laurén Achim Grelle Olli‐Kalle Kauppinen Ola Lagnvall Anders Lindroth Kai Rasmus Magnus Svensson Per Weslien |
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| Institution: | 1. Plant Ecophysiology and Climate Change Group, Department of Biological and Environmental Sciences, University of Helsinki, , 00014 Finland;2. Department of Biological and Environmental Sciences, University of Jyv?skyl?, , 40014 Finland;3. Department of Land and Water Resources Engineering, Royal Institute of Technology, KTH, , 100 44 Stockholm, Sweden;4. Aalto University School of Engineering, Department of Civil and Environmental Engineering, , 00076 Aalto, Finland;5. Finnish Forest Research Institute, Joensuu Research Unit, , 80101 Joensuu, Finland;6. Department of Physical Geography and Ecosystems Analysis, Lund University, , S‐223 62 Lund, Sweden;7. Finnish Environment Institute, Jyv?skyl? Office, , 40500 Jyv?skyl?, Finland;8. Department of Soil and Environment, Swedish University of Agricultural Sciences, , 750 07 Uppsala, Sweden |
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| Abstract: | Leaf area index (LAI) and canopy coverage are important parameters when modelling snow process in coniferous forests, controlling interception and transmitting radiation. Estimates of LAI and sky view factor show large variability depending on the estimation method used, and it is not clear how this is reflected in the calculated snow processes beneath the canopy. In this study, the winter LAI and sky view fraction were estimated using different optical and biomass‐based approximations in several boreal coniferous forest stands in Fennoscandia with different stand density, age and site latitude. The biomass‐based estimate of LAI derived from forest inventory data was close to the values derived from the optical measurements at most sites, suggesting that forest inventory data can be used as input to snow hydrological modelling. Heterogeneity of tree species and site fertility, as well as edge effects between different forest compartments, caused differences in the LAI estimates at some sites. A snow energy and mass balance model (SNOWPACK) was applied to detect how the differences in the estimated values of the winter LAI and sky view fraction were reflected in simulated snow processes. In the simulations, an increase in LAI and a decrease in sky view fraction changed the snow surface energy balance by decreasing shortwave radiation input and increasing longwave radiation input. Changes in LAI and sky view fraction affected directly snow accumulation through altered throughfall fraction and indirectly snowmelt through the changed surface energy balance. Changes in LAI and sky view fraction had a greater impact on mean incoming radiation beneath the canopy than on other energy fluxes. Snowmelt was affected more than snow accumulation. The effect of canopy parameters on evaporation loss from intercepted snow was comparable with the effect of variation in governing meteorological variables such as precipitation intensity and air temperature. Copyright © 2012 John Wiley & Sons, Ltd. |
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| Keywords: | snow modelling canopy forest energy balance |
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