Parameter Estimation of Stomatal Conductance Model to Predict Whole-Tree Transpiration Rate and Spatial Distribution of Leaf Surface Temperature Within the Canopy

Abstract

Urban heat during summer has recently become a serious issue. Although urban trees have a cooling effect, this effect must be evaluated quantitatively for effective landscape and streetscape design. However, models capable of predicting hourly changes in typical tree transpiration under summer conditions at the whole-tree scale rather than the individual-leaf or forest scale are lacking. In addition, leaf surface temperatures in the lower canopy, which significantly affect the radiative environment of pedestrians, must be accurately predicted. Nevertheless, the prediction accuracy of heat balance changes on leaf surfaces due to transpiration has not been adequately validated. Such models must also consider plant physiological responses, which vary with the surrounding physical environment, to ensure high accuracy. In this study, a literature review was performed to identify transpiration and stomatal conductance models that can predict typical transpiration and heat balance properties. Subsequently, hourly transpiration rate changes of the whole tree and spatial distribution of leaf surface temperatures in the lower canopy were measured. The parameters of the stomatal conductance model were also estimated to enable predictions using both models combined. The present model is novel because it reproduces whole-tree transpiration rate characteristics and leaf surface temperature trends in the lower canopy.