田間蒸發散量之估測與應用

Abstract

田間蒸發散量的多寡不僅直接影響土壤中的有效水分含量及作物產量，也是擬定灌溉計畵和進行水資源規劃時的重要參考資料。本文首先說明測定地表蒸發散量的技術，介紹利用氣象資料推估地表蒸發散量的方法，然後論及估計區域蒸發散量的注意事項，以及農業上可能的應用方向使用滲漏計法和微氣象法可以測得田間蒸發散量短期間內的動態變化，是計算作物係數和評估作物水分利用效率的重要基礎資料。氣象資料只適合推估長期的盆面蒸發散量，若要推估大區域盆面蒸發散量的分佈，還必須考量所使用氣象測站資料的適用範圍與測站密度就台灣西南部地區而言，利用氣溫和日射資料可以合理推估月累積盆面蒸發量之空間分佈。 Field evapotranspiration affects not only soil available water and crop yields but also water resources management and planning. In the paper, measurement techniques and estimation methods for determining field evapotranspiration were discussed. Spatial distribution of regional potential evapotranspiration and its agricultural applications were also discussed. Both lysimetric and micrometeorological methods can provide dynamic changes of field evapotranspiration which serves as the basis of computing crop coefficients and crop water use efficiency. Meteorological data are suitable for estimating long-term field evapotranspiration. To estimate regional potential evapotranspiration from meteorological data, the representative range of data used and density of available stations must be taken into consideration. For southwest region of Taiwan, spatial distribution of monthly pan evaporation can be reasonably estimated by mean air temperature and solar radiation.