利用潛熱通量資料驗證水稻田蒸發散模式

Abstract

決定水稻的需水量對灌溉計畫非常重要。本研究利用水汽量測系統量測蒸發散量構成因子，以估算水稻田實測資料並以評估四種估算潛勢能蒸發散模式之準確度。結果顯示，以溫度為輸入值之Hargreaves and Samanni 法高估蒸發散量，相反的，以輻射量為輸入值之Miakkink 法則低估，Penman-Monteith 法和其簡化方程式(Priestley-Taylor method 法)則較能符合實測值。除此之外，本研究另一目的即利用蒸發散量實測值及氣象資料發展出適合之水稻作物係數，以Penman-Monteith 方法估測潛能蒸發散量，比較由水汽量測系統所量測之實測值。結果顯示，水稻一期作之四個生育時期(幼苗期、分蘗期、抽穗期及成熟期)之作物係數，分別為0.92、1.00、1.13及0.89；二期作則為1.01、1.11、1.23 及0.93。 Determining water requirement of rice is important for paddy field irrigation plan. The objectives of this study were to measure evapotranspiration with eddy correlation system, and to validate four empirical equations of potential evaportranspiration by comparing the model’s estimated values to calculated values of latent heat flux from paddy field. The results showed that evaportranspiration was overestimated by Hargreaves and Samanni method based only on temperature as input. On the other hand, evaportranspiration was underestimated by Makkink method based only on solar radiation as input. The Penman-Monteith method and its derived simplified form (Priestley-Taylor method) gave better fitted to the actual measured values. Moreover, the crop coefficient (kc) was developed from crop evaportranspiration (ETc) calculations and weather data. The reference/potential evapo- transpiration (ETo) estimated by Penman- Monteith method were compared with the calculated value of ETc from eddy correlation system. Results indicated that the crop coefficients suitable for first season rice crop in the four growth stages, namely, seedling, tilling, heading and maturity, were 0.92, 1.00, 1.13 and 0.89, respectively. The coefficients suitable for the second season rice crop were 1.01, 1.11, 1.23 and 0.93, respectively.