Pine forest microclimate simulation using different diffusivities |
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| Authors: | Sven Halldin Anders Lindroth |
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| Institution: | (1) Division of Hydrology, Uppsala University, Västra »gatan 24, 752 20 Uppsala, Sweden;(2) Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden |
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| Abstract: | Proper understanding of, e.g., evaporation from a forest requires an understanding of its microclimate. A well established, steady-state model was used to simulate microclimate and evaporation of a sparse pine forest in central Sweden. Model input included profiles of turbulent diffusivity, boundary-layer resistance, stomatal resistance, wind speed, net and global radiation and needle area density. Momentum balance, energy balance and exponentially decreasing diffusivities were used to study the sensitivity of the evaporation rates and of the temperature and humidity profiles. Model output proved to be unreliable when measured temperature and humidity at the bottom of the stand were used instead of a measured ground heat flux as the lower boundary condition. Energy balance diffusivity was usually larger than momentum balance diffusivity at the canopy top but decreased rapidly to a minimum at approximately the height where the momentum balance diffusivity had its maximum. Energy balance diffusivity commonly showed a secondary maximum below the height of the maximum needle area density. Profiles of Richardson number showed that thermal effects became important just below the canopy top. Bluff-body effects distinguished the energy balance from the momentum balance diffusivity and both were subject to shelter effects. Total evaporation was not very sensitive to the choice of diffusivity when soil heat flux was given as the lower boundary condition. |
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