本研究以PenPan V2 Model與PenPan V3 Model中的空氣動力學與能量平衡理論，探討臺灣十個測站的A型及20公分蒸發皿的蒸發量成因與比例。由分析結果得知，於A型蒸發皿，空氣動力及輻射對蒸發的影響分別為21%與79%；於20公分蒸發皿，空氣動力及輻射對蒸發的影響分別為25%與75%。估計邊壁效應對皿蒸發量的影響，並推求自由水面蒸發占皿蒸發量的比例，得到A型蒸發皿的邊壁效應占27%，自由水面蒸發量為皿蒸發量的73%；20公分蒸發皿的邊壁效應占58%，自由水面蒸發量為皿蒸發量的42%。本研究利用兩蒸發皿的月蒸發量及邊壁效應影響比例資料，推估所得自由水面蒸發量，分別與A型及20公分皿的蒸發量資料建立截距為零的線性回歸關係式，得到利用皿蒸發量推估自由水面蒸發量的簡便公式，將A型皿觀測值乘以0.74可得自由水面蒸發量；將20公分皿觀測值乘以0.54可得自由水面蒸發量。本研究進一步利用兩推估的自由水面蒸發量，並加入全天空日射量及氣溫，建立自由水面蒸發公式，再考慮應用到全臺灣通用性，發展出三組分區公式。本研究將自由水面蒸發公式應用於臺灣重要水庫的蒸發水量估算，對於水庫水資源及水平衡的掌握，提供簡便且精確的水庫蒸發水量估計值。

This study used the aerodynamics and energy balance theories to investigate the pan evaporation and to develop the free water surface evaporation formula. PenPan V2 Model and PenPan V3 Model were applied to estimate the evaporation from the Class A evaporation pan and the 20-cm evaporation pan, respectively, at 10 stations in Taiwan. Analysis results revealed that for the Class A evaporation pan, the aerodynamics and radiation contribute 21% and 79% of the evaporation rate, respectively; for the 20-cm evaporation pan, the aerodynamics and radiation contribute 25% and 75%, respectively. The study estimated the influence of side wall effect on the evaporation and inferred that the free water surface evaporation accounts for 73% of total evaporation in the Class A evaporation pan and 42% in the 20-cm evaporation pan, with side wall effect contributing 27% and 58%, respectively. This study used monthly evaporation data and side wall effect ratios from both evaporation pans to estimate the free water surface evaporation. A simple method to estimate the free water surface evaporation is to multiply the observations of the Class A evaporation pan by 0.74, and to multiply the observations of the 20-cm evaporation pan by 0.54. This study further developed three regional free water surface evaporation formulae by utilizing the solar radiation and air temperature. These regional formulae were applied to estimate the free water surface evaporation from major reservoirs in Taiwan.

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