作为蒸散量的测算和环境评价的一种方法，通过近年来对三温模型的研究，该文详细探讨了植被蒸腾扩散系数（hat），并通过实验验证了它在不同环境条件下的特性和应用前景。在该模型中，hat的表示式为hat=（Tc-Ta）/( Tp-Ta)，式中Tc、Tp和Ta分别为冠层温度、没有蒸腾（蒸腾量为零）的冠层温度和气温。理论上，植被蒸腾扩散系数的取值范围为hat≤1，hat的取值范围可以决定植被蒸腾量的大小，该系数越小， 蒸腾量越大。为了证明hat的这些特性，在1994～1999年的5年间，用3种作物（高粱(Sorghum bicolor)，番茄( Lycopersicon esculentum)和甜瓜(Cucumis melo)）进行了5次试验。实验结果表明: hat值与感热通量比率（H/Hp）的值近似相等，二者之间回归线的斜率接近为1，截距接近0，回归系数为r2=0.70。此外，hat值不仅能较好地反映植物根系区的土壤水分状况、也能较好地反应天气状况。在缺水条件下，hat主要受根部区域的水分状况影响。 所以，hat可作为作物水分亏缺的指标。当植被受到其它环境胁迫（污染、高温等）时，hat可作为评价环境质量的指标。植被蒸腾扩散系数的主要优点不仅是能很好地反映蒸腾过程和确定蒸腾量，而且容易测得，便于遥感应用。
Background and Aims 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 (hat) and to verify its characteristics under various environmental conditions.
Methods The hat is defined as (Tc-Ta)/(Tp-Ta), where Tc, Tp, and Ta are temperatures of vegetation canopy, a non_transpiring canopy, and air, respectively. Five experiments were carried out to verify the proposed coefficient.
Key Results Theoretical analysis and experimental results show hat≤1. If Tc=Tp, hat has its maximum value (hat = 1) and transpiration rate has its minimum value (zero). This boundary is determined by lack of water for transpiration. On the other hand, when hat 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.
Conclusions Therefore, hat can determine transpiration rate from its minimum value to its maximum value. A lower value of hat corresponds to a higher transpiration rate.