蒸發散量Penman-Monteith估算方程式最適蒸汽壓力差計算式之評估

Assessment on the Optimal Applicability of Vapor-Pressure-Deficit Calculation Methods in the Penman-Monteith Equation for Estimating Evapotranspiration

宋易倫(Sung Yi-Lun)

指導教授 ： 張德鑫

中原大學/工學院/土木工程學系/碩士(2007年)

https://doi.org/10.6840/cycu200700326

摘要

蒸汽壓力差(vapor pressure deficit, VPD)是表達大氣蒸發能力重要指標，在蒸發散量混合法或Penman-Monteith型態估算模型亦居重要成分。眾多蒸發散量估算方程式中涉及VPD之計算，由於地域性氣候環境背景特性、溫度或濕度或露點等各氣象因子引用考量、取樣資料頻率多寡、資料平均方式及資料組合方式等之不同，目前有超過二十種以上VPD計算式，為國內外著名機構或學者推荐在世界各地廣泛應用。
本文以台灣地區各地農業氣候分區2002-2003年實際氣象觀測記錄，應用頻率分析法(frequency approach)及統計指標法(statistical index approach)進行評估。其中，頻率分析法係藉誤差(error)、全距(range)、優劣排序及出現頻率(frequency)，並匹配權重指數(weighted index, WI)予以量化方式；統計指標法係採根均方差(root mean square error, RMSE)、相關係數(coefficient of correlation, R2)及效率係數(coefficient of efficiency, CE)三項客觀統計指標，分別進行國內外機構或學者所推荐VPD計算式，在國內本土環境應用上適用性之評估。
本文目前整理的VPD計算式共有3種型態26款計算式，分析結果顯示，以頻率分析法而言，各地農業氣候分區均呈現，VPD計算式以24個時溫度日平均為飽和蒸汽壓力，與濕球下陷量為實際蒸汽壓力，具誤差最少、全距最小、出現頻率最多及最高權重指數，性能表現最佳，這樣的結果，對照統計指標法之檢測評估，同樣具最低RMSE、R2值0.99以上及最大CE，性能表現優於其他所有VPD計算式，兩者結果不僅一致，而且皆屬混合法型態。
因此，綜合上述兩項方法評估結果，本研究建議：
1.以往國際性著名機構或國外學者所推薦VPD計算式，並不適合在台灣繼續應用。
2.第25款VPD計算式為：24個時溫度日平均為飽和蒸汽壓力，與濕球下陷量為實際蒸汽壓力，堪稱最適台灣氣候環境本土化VPD計算式，可在台灣各農業氣候分區之應用。

關鍵字

蒸發散量 ； 頻率分析法 ； Penman-Monteith ； 消耗水量 ； 蒸汽壓力差 ； 統計指標法

並列摘要

Vapor pressure deficit (VPD) is a significant index for the capacity of evaporation, and also plays an important parameter in estimating evapotranspiration, particularly in the combination or Penman-Monteith type equations. Due to the difference on the environmental climate characteristic, climate variables selected, number of records sampled, averaging means and compoundable ways, there are 3 types 26 VPD calculation methods which were widespreadly used for estimating evapotranspiration around the world.
Those methods for VPD calculation were analyzed and compared using 2002-2003 data from meteorological stations to determine the most appropriate method that can be applied in Taiwan. Frequency Approach (FA) and Statistical Index Approach (SIA) were used to evaluate and compare the results and applicability among these methods in Taiwan. Error, range, frequency, and weighted index (WI) were used in FA. Three objective statistical indexes, root mean square error (RMSE), coefficient of correlation (R2), and coefficient of efficiency (CE), were used in SIA.
For the FA, the results indicated that the VPD calculation using mean of 24 hourly temperature values as saturation vapor pressure, and wet-bulb depression as actual vapor pressure yielded the lowest error, the least range, and the most frequency with the highest WI. These outcomes were as well as the SIA with the lowest RMSE, R2 higher than 0.99 and the highest CE. The performance of this VPD method was proved better than all other VPD methods. The findings were not only consistent with attempts at FA and SIA in this paper, but also belonged to a hybrid type VPD method.
Accordingly, this VPD method was recommended to apply in Taiwan. However, the other VPD calculation methods in literature were not recommended to be used in Taiwan.

並列關鍵字

Vapor-Pressure-Deficit ； Penman-Monteith ； Consumptive Use of Water ； Frequency Approach ； Statistical Index Approach ； Evapotranspiration

參考文獻

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