摘要 本研究建立垂直整合之水文氣象即時觀測系統，探討地表過程之蒸發散特性。主要利用垂直多點量測的土壤水分觀測儀器(Capacitance Probe)，即時觀測土壤水分變動，以估計非降雨條件下之地表過程蒸發散造成的土壤水分損失，並與其他採用微氣象觀測資料推估蒸發散的方法(Penman-Monteith法、Priestley-Taylor法、Bowen ratio法及空氣動力法)作比較分析。研究分析時，分別以日平均資料進行長期年間蒸發散量變化討論；以及10分鐘資料探討微氣象因子對短期日間蒸發散量的影響。 長期年間研究結果顯示，當土壤潮濕時以Penman-Monteith、Priestley-Taylor和Bowen ratio法，所估計的蒸發散量與土壤水分損失量相似；土壤乾燥時，估計蒸發散量和土壤水分損失量的比值會與表層土壤含水量呈現指數關係。利用建立的指數關係式將改善土壤乾燥低含水量時的蒸發散估計，修正後的四種方法以Penman-Monteith法估計之蒸發散量與土壤水分損失量的差異最小，但此方法估計時所需氣象資料最多；而以空氣動力法所推估的蒸發散量與土壤水分損失量差異最大。 短期日間的研究結果，當環境潮濕時，蒸發散量的推估以Penman-Monteith法計算之蒸發散量最為接近土壤水分損失量；Priestley-Taylor法因只考慮地表可利用能量，無法反映出能量外的其他氣象因子影響；Bowen ratio法受到方法本身的限制，不適用於短期日間，高時間解析度的蒸發散估計。 Abstract This study developed a vertically integrated hydrological and meteorological real-time monitoring system to investigate the evapotranspiration (ET) of land processes. The multisensor capacitance probe was applied to measure the variation of soil water content for determining the loss of soil water accounting for ET over dry days. The results were compared with other micro-meteorological methods, including the Penman-Monteith equation, the Priestley-Taylor equation, the Bowen ratio method, and the vapor gradient method, for estimating ET or potential ET. The discussions were presented in two parts, the first one used daily average data to analyze the daily ET variations; the second part used ten-minute resolution data to analyze the diurnal ET variation associated with the micro meteorological factors. The results of the daily analyses were given as the following. Under wet soil conditions, the amounts of ETs estimated by the Penman-Monteith equation, the Priestley-Taylor equation, and the Bowen ratio method showed the similar values with the measured loss of soil water. Under dry soil conditions, the ratios of the estimated ETs to the measured soil-water losses associated with the surface soil water content were found to have an exponential relation. With this exponential relation, the differences between the estimated ET and the water loss can be reduced. Among all methods compared in this study, the Penman-Monteith equation is the best one to estimate ET and the only draw back is the requirement of numerous meteorological data. The vapor gradient method were found to be disappointed on estimating daily ET in this study The results of the short-time diurnal analyses are presented as below. Under wet soil conditions, the amounts of ETs estimated by the Penman-Monteith equation were most close to the measured loss of soil water. The Priestley-Taylor equation only includes the available energy and is unable to capture the influences of other meteorological variances on ET. The ETs estimated by the Bowen ratio method is oscillated due to the intrinsic unstable approach, so it is unsuitable for estimates ET using high temporal resolution data.
