SURFACE CONDUCTANCE OF AMAZONIAN PASTURE - MODEL APPLICATION AND CALIBRATION FOR CANOPY CLIMATE

Bulk stomatal conductances of Amazonian pasture, derived from micrometeorological measurements, are used to calibrate existing climate-based models of stomatal response. In the models, specific humidity deficit and solar radiation are the dominant controls on transpiration, with soil moisture providing the necessary seasonality. This paper relates hourly conductances to canopy-space climate to achieve parameters which are substantially independent of the aerodynamic characteristics of the measurement site, and a method is described for implementing this scheme within resistance-based models of surface fluxes for use in general circulation models. The results are compared with those from simpler methods using unmodified climate data measured at 3.5 m above the pasture. Although additional uncertainty is introduced by the estimation of canopy climate, reasonable accuracy is achieved in predicting evaporation at this site. It is demonstrated that errors may be introduced if the difference between measurement height for calibration and reference height for application is ignored.