全球氣候暖化，對水文循環中蒸發散現象影響至鉅，而地表水分蒸發散量之預測一直是許多研究的重點。以往研究蒸發量之實驗，大多於戶外特定的實驗埸地，以蒸發皿(Evaporation Pan)或土壤測滲儀(Lysimeter)進行蒸發量之觀測，再與當時的氣象參數迴歸求得適用於該地之經驗公式。但此類研究，受限於實驗時之氣象條件，蒸發散量與時俱變，且可能會影響蒸發散的因素太多，往往不易由量測結果瞭解蒸發過程中的發生機制，亦無法釐清主要的影響參數。本研究利用風洞實驗，控制風速、淨輻射量和土壤含水量，在各種不同狀況下，進行裸土(Bare soil)水分蒸發的實驗研究，並與前人建議之蒸發量公式進行比對，俾找出較佳的土壤蒸發量預測公式，研究結果顯示風速、淨輻射量和土壤含水量皆對土壤水份蒸發有顯著的影響，且Penman Ea (1948)和Turner (1966)的潛勢蒸發散預測公式最接近風洞實驗中飽和土壤之量測結果。另利用土壤阻抗模式求得土壤阻抗係數，並代入Penman-Monteith公式計算未飽和土壤之蒸發量，其結果顯示Penman-Monteith公式可預測未飽和土壤的蒸發量。 Global warming has significant impact on the evapotranspiration in hydrologic cycles; in consequence, the evaporation process from soil surface has been investigated by numerous studies. Most of evaporation prediction models were based on the measurements of evaporation pans and lysimeters in the field. In this study, we carried out a series of wind tunnel experiments to study the effect of wind velocity, net radiation and soil moisture on the evaporation rate of bare soil. The experimental results were compared with several evaporation equations, and showed that wind velocity, net radiation and soil moisture all have notable effects on evaporation rate. In addition, the prediction equations suggested by Penman (1948) and Turner (1966) gave the most accurate evaporation rates. Furthermore, a soil resistance model was developed and integrated with Penman-Monteith equation to predict evaporation rate of under-saturated soil. The model prediction showed good agreement as compared with the measured data.
