蒸發散為水文循環中重要的一環，但因為影響蒸發散的參數（譬如風速、濕度、溫度、輻射量、土壤含水量、植物種類等）太多，利用經驗公式估算蒸發散量往往有很大的誤差。而蒸發皿是量測逐日蒸發散量最簡易、最常用的方法，再利用皿係數便可推估自由水面或地表的蒸發散量。但前人的研究發現蒸發皿係數 (Pan coefficient)會隨季節而變，介於0.35~0.85之間，也有很高的不確定性。本計畫預備研究風速、輻射量、蒸發皿內水深對皿係數的影響，預備在控制的環境下，進行一系列的實驗來研究蒸發皿係數如何受到這些參數的影響，並預備以稱重法直接量測裸土蒸發量和短草蒸散量，與蒸發皿之結果互相比較，以瞭解蒸發散的機制，釐清土壤蒸發與植物蒸散兩者之間的關係，並期望建構一個客觀、準確的皿係數的計算模式。Evaporation pans and pan coefficient have been widely used to measure and calculate evaporation rate of water body and/or land surface. However, there is a great uncertainty in pan coefficient, since it varies seasonally in the range of 0.35~0.85. This study plans to use wind tunnel experiment to investigate the relationship between pan coefficient and environmental parameters, such as wind speed, solar radiation, and water depth. A series of controlled experiments will be carried out to increase our understanding of pan coefficient. The transpiration rates of short grass and evaporation rates of bare soil will be measured by weighting method in order to compare with the results of evaporation pan. Based on the experimental results, a physical model will be developed to calculate the pan coefficient.
研究期間 : 9808 ~ 9907
