勢能蒸發散計算方法應用於中海拔地區之比較

Abstract

為了探討勢能蒸發散計算公式在中海拔地區的適用性，本研究利用日月潭氣象站與阿里山氣象站之2001年至2005年氣象觀測資料為基礎，選擇了六種勢能蒸發散公式，Hamon、Thornthwaite、Makkink、Priestly-Taylor、Turc及Penman-Monteith公式，經過六種公式計算結果並分別與Pan Method計算結果比較其勢能蒸發散表現。在日月潭氣象站的比較結果，以輻射為基礎的公式之Priestly-Taylor公式不論是計算日勢能蒸發散量或者是計算月勢能蒸發散量上，與Pan Method計算結果之相關性高，且平均絕對離差以及均方根誤差皆為最小；而在阿里山氣象站則是Makkink公式的計算結果與Pan Method的計算結果相關性高，且平均絕對離差以及均方根誤差皆為最小。在兩個氣象站都是以考慮輻射項的公式有較好的相關性，此與劉(2004)提出的研究結果近似。 日月潭氣象站包含輻射項的公式的計算結果中顯示，使用日淨輻射量當作參數來計算的Turc公式全年皆有高估的情形，Makkink公式則是呈現低估的情形，Priestly-Taylor公式夏季期間相當符合，冬季則稍有低估。 阿里山氣象站包含輻射項的公式的計算結果中顯示，使用日淨輻射量當作參數來計算的Priestly-Taylor公式，其月勢能蒸發散量計算結果在夏季期間會有高估的情況。而利用日輻射量當作參數計算的Makkink公式與Turc公式，Turc公式亦呈現夏季高估的情形，Makkink公式其月平均勢能蒸發散量計算結果與Pan Method的計算結果趨勢則相當符合，冬季稍有低估情形。因此使用這些公式計算勢能蒸發散量時，必須考慮當地輻射項的差異，以避免計算結果與實際的蒸發散變化趨勢不相符。

This research choose six calculating potential evapotranspiration(PET) methods compared with Pan method to discuss the suitability of potential evapotranspiration in medium elevation area such as in Alishan and in Sun Moon Lake. Six calculating methods include Hamon method, Thornthwaite method, Makkink method, Priestly-Taylor method, Turc method, and Penman-Monteith methods. In Sun Moon Lake Meteorological station, according to daily PET and monthly PET calculated by six methods, radiation-based Priestly-Taylor method has the best correlation with Pen method. However, Makkink method has the best correlation with Pen method in Alishan meteorological station. Results in both meteorological stations show that calculating methods considered radiation would have better suitability, which is similar to Liu’s study in 2004. In Sun-Moon Lake meteorological station, the monthly PET calculated by Turc Method,using daily net radiation as a parameter, will be overestimated in whole year. Makkink method, using daily radiation as a parameter, will be underestimated in whole year. Priest-Taylor Method, using daily radiation as a parameter, will be underestimated during winter. In Alishan meteorological station, the monthly PET calculated by Priestly–Taylor Method,using daily net radiation as a parameter, will be overestimated in summer period. However, Makkink and Turc methods using daily radiation as a parameter will have similar value to Pan method. Turc Method will overestimated during summer and Makkink Method will be underestimated during winter. Therefore, when using those methods to calculate potential evapotranspiration, it is necessary to consider the difference of local radiation to avoid discrepancy between the calculated result and data tendency.