A thermal exitance and energy balance model for forest canopies

A steady-state thermal radiance model to compute thermal exitance and energy balance within forest canopies is described. The model treats fully leafed canopies as discrete ensembles of leaves partitioned into slope-angle and height classes. Short-wave energy flux absorbed within the canopy is estimated by solving simplified radiosity equations. Sensible heat exchange is estimated using a logarithmic wind profile above the canopy and a modified exponential profile within the canopy. The latent heat boundary layer resistance is estimated from site-specific measurements summarizing the effects of solar irradiance, air temperature, and vapor pressure deficit on stomatal conductance. Example comparisons for a dense spruce-fir forest study site in central Maine are given. For clear days the resulting root mean square error in modeled versus measured canopy temperatures was 1.2°C. Corresponding errors in latent and sensible heat flux energy budget terms were 30 and 32 W/m^-2, respectively. For partly cloudy days the root mean square error in predicted temperature was 1.0°C and corresponding errors in latent and sensible heat were 40 and 110 W/m^-2