A HEAT-BALANCE MODEL FOR PARTIALLY VEGETATED SURFACES

A steady-state thermal balance model has been designed to enable the p rediction of the radiative temperature of partially vegetated surfaces . Vegetation is assumed to be a horizontally homogeneous but porous la yer partially covering a soil surface. Short-wave and long-wave energy fluxes absorbed within the vegetation are estimated by solving simpli fied radiation equations. Sensible and latent heat exchange is estimat ed using a logarithmic and linear wind profile above the vegetation an d a modified exponential profile within the vegetation. The stomatal r esistance for latent heat flux is estimated from the equation summariz ing the effect of solar irradiance, air temperature, and vapor pressur e deficit on stomatal conductance. Based on the energy balance and the heat fluxes and water vapor continuity in the soil-vegetation-atmosph ere system, the temperature of the foliage elements and the soil under neath is determined. The model has been tested by comparing simulated radiative temperatures with observed data gathered in short grass and a wheat field. The simulated and measured results match reasonably wel l. In order to examine whether the model responds to the change of a s pecific weather or material parameter, a sensitivity analysis of the m odel is considered. (C) 1997 Elsevier Science B.V.