THREE TEMPERTURE (3T) MODEL—A METHOD TO ESTIMATE EVAPO_TRANSPIRATION AND EVALUATE ENVIRONMENTAL QUALITYY BASED ON SURFACE TEMPERATURE. IV. PLANT TRANSPI_RATION TRANSFER COEFFICIENT

Abstract

Vegetation transpiration rate sensitively responses to environmental stress introduced by air pollution, environmental degradation (soil and water), and global change. Based on energy balance analysis, by introducing the temperature of a canopy without transpiration, the objectives of this study are to propose a remotely measurable plant transpiration transfer coefficient (h_(at)) and to verify its characteristics under various environmental conditions. The hat is defined as (T_(c)-T_(a))/(T_(p)-T_(a)), where T_(c), T_(p), and T_(a) are temperatures of vegetation canopy, a non_transpiring canopy, and air, respectively. Five experiments were carried out to verify the proposed coefficient. Theoretical analysis and experimental results show h_(at)≤1. If T_(c)=T_(p),hat has its maximum value (h_(at)=1) and transpiration rate has its minimum value (zero). This boundary is determined by lack of water for transpiration. On the other hand, when h_(at) has a minimum value, transpiration can reach its maximum value (potential transpiration rate). This boundary is determined by the avail ability of energy for transpiration. Therefore, h_(at) can determine transpiration rate from its minimum value to its maximum value. A lower value of h_(at) corresponds to a higher transpiration rate.