近幾年全球暖化對環境有不可忽略的影響，瞭解水文循環可有助於因應此現象。陸地上植物蒸散為水文循環當中重要的一環。植物蒸散由葉部氣孔調控，而氣孔張開的程度主要由植物生理對環境條件的反應而定。氣孔張開的程度通常由氣孔導度來表示，主要可利用二種模式來模擬氣孔導度。Jarvis模式使用經驗法，其原理為建立氣孔導度與環境條件變異之間的關係，並假設氣孔導度與光合作用速率無關。Ball-Berry模式使用半經驗法，其原理以氣孔導度與內部二氧化碳濃度和光合作用之間的密切關係為基礎。二種模式在土壤不缺水分的情況下皆相當正確地計算氣孔導度，但在缺水的情況下，或研究不同樹種時，此二個模式皆呈現一些缺陷。因此，為了應付各種環境條件，許多學者調整原本的模式，而得到與實際觀測更接近的結果。

In the context of a changing environment, a better understanding of the water cycle is needed to adapt to global warming. On land, vegetation transpiration is a very important part in the water cycle. Transpiration is regulated by leaves stomata, which the degree of aperture representing stomatal conductance mostly depends on physiological factors responding to environmental conditions. Two major models have been used to simulate stomatal behavior under different environmental conditions. The Jarvis model, which is largely empirical, links stomatal conductance to environmental conditions and assumes that stomatal conductance is independent of rate of photosynthesis. The Ball-Berry model, which can be classified as semi-empirical, is based on evidence that a tight relationship exists among stomatal conductance, internal CO2 concentration and photosynthesis. The two models perform well when environments are subjected to low to moderate water stress; however, they may not correctly calculate stomatal conductance when under water stress or for various tree species. Thus, further studies have modified the parameters to better estimate stomatal conductance under different conditions, and have obtained satisfying results in most cases.