在水文循環過程中，蒸發散對於區域性水資源評估及管理是相當中重要的水文因子。本研究主要目的以氣象資料評估蒸發散量及蒸發皿蒸發量，來推估蒸發皿係數，進而建立區域蒸發皿係數之分布圖，並探討蒸發皿係數之區域空間分布。另外，探討前人發展之蒸發皿係數(Kpan)經驗式並利用Penman-Monteith法與蒸發皿(Epan)之比值來進行實際蒸發皿係數之評估比較。本研究利用統計指標分析上述兩種蒸發皿係數方式所評估的蒸發散量之差異，以期尋求較簡單之經驗方程式解決氣候參數資料之不足等問題。結果顯示，全台灣區域與南、北部區域的蒸發散量與蒸發皿蒸發量均有相同的趨勢分布，蒸發散量呈現由北向南及由內陸高山區逐漸往沿海平原區遞增的情形。而在蒸發皿係數方面，Kpan值呈現由南向北遞增趨勢，且受區域性與季節性變化的影響。此分布情況可以正確的評估出真實蒸發散量做為區域性水文評估及管理之參考資訊。
　　於文中選用五個前人已發展蒸發皿經驗公式進行蒸發散量評估結果，顯示本研究利用較簡單的蒸發皿係數經驗式來替代繁雜的Penman-Monteith法，減化在計算過程所需要的眾多氣象參數資料，發現經驗式應用於台灣地區各氣象站中，除了山區測站評估相對誤差較大，其值平均為±25%；在其他平原地區測站推估蒸發散量有其參考價值，其相對誤差平均為±10%。本研究建議日後推估區域性蒸發散量，在資料不足之情況下亦可使用蒸發皿係數經驗式進行評估。

　　Evapotranspiration (ET) is an important component of hydrologic budgets, as well as plays an active role in the regional water resources assessment and management. The purpose of this study is to use the meteorological data to estimate the regional reference evapotranspiration and to assess the spatial distribution maps of pan coefficient (Kp) in study area. In addition, five empirical equations of pan coefficient by previous researches are applied to estimate the regional reference evapotranspiration. Moreover, In order to improve the absence of climatic data and to confirm the applicability of five empirical equations, results of empirical equations of pan coefficient compared with the ratio of Penman-Monteith combined method (ET) and pan evaporation (ETpan) recorded (Kp = ET / Epan). Finally, the differences of two methods are calculated by statistical analysis.
　　Results shows the reference evapotranspiration and pan evaporation have similar regional distribution patterns in the north and south of Taiwan. All with the high values being in the lower region and the low values being in the upper region；large values are found in west plain, the small are obtained in central mountain area of Taiwan. The pan coefficient (Kp) also varies both regionally and seasonally. The resultant map shows high Kp values towards the lower region, and small Kp values are found in the upper region. Several spatial distribution maps of the reference evapotranspiration have provided valuable information in water resources planning and management in thesis. Due to the insufficiency of the most meteorological stations data, it is difficult to assess the regional reference evapotranspiration. By applying empirical equations are in accord with the results of the Penman-Monteith combined method which have estimated performance. The relative error of both methods in central mountain areas are about ±25%, and in other plains are about ±10%, despite the fact that these empirical equations are to simplify the assessment of the regional reference evapotranspiration.

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