Understanding the water relations of Eucalyptus trees plays an important role in finding solutions to dryland salinity in southern Australia. A model for studying structure–function relationships in isolated tree crowns (radiation absorption, transpiration and photosynthesis, RATP) was parameterized to permit the seasonal transpiration course of a Eucalyptus salmonophloia tree to be quantified. Model responses to different parameterizations were tested in a sensitivity analysis. Predictive quality was mostly affected by the accuracy of information about leaf area density and stomatal responses to air vapor pressure deficit, and to a lesser extend by foliage dispersion. Assuming simple, non-synergistic influences of changes in photosynthetic active radiation and air vapor pressure deficit on stomatal transpiration control, the model was able to simulate the daily water uptake of E. salmonophloia trees with reasonable predictive quality during an entire season. In order to more precisely simulate short-term (i.e. diurnal) water use dynamics, the model must be extended to account for hydraulic and chemical controls of stomatal regulation of crown energy balance.