濕草地上的植披阻抗

Abstract

植披阻抗(canopy resistance)為在使用Penman-Monteith法預測蒸發散量時的重要參數。因此為了預估蒸發散量，必須了解植披阻抗的特性。Pauwels 和 Samson在2006年時，在一斜坡上的濕草地比較不同預測植披阻抗的方法。結果顯示Katerji and Perrier method (Katerji and Perrier, 1983)有較佳的預估能力。在本研究中，我們嘗試利用相同的概念並比較六個預估植披阻抗的方法，包含：Jarvis type equation (Jarvis, 1976; Stewart, 1988)，Jarvis-Blanken and Black method (Blanken and Black, 2004)，Todorovic method (Todorovic, 1999)，Katerji and Perrier method，新方法和固定的植披阻抗值。研究地位於愛爾蘭的西南方科克縣 (Ireland, County Cork(51°〖59〗^' N 8°〖46〗^' W))，主要物種為多年生黑麥(Lolium perenne L.)。本研究利用渦流相關法(eddy covariance)量測濕草地上的潛熱通量。觀測的植披阻抗由Penman-Monteith法以及量測的熱及潛熱通量回推而得。研究結果顯示，潛熱通量的預估值好壞與植披阻抗的預估值好壞相關性不大。此外，Katerji and Perrier method和新方法在本研究中相對其他方法皆可較佳的預測植披阻抗以及潛熱通量。

Canopy resistance is a key parameter for implementing the Penman-Monteith equation, which is a well-known method of estimating evapotranspiration. In order to estimate evapotranspiration, it is essential to know the knowledge concerning canopy resistance. Recent research (Pauwels and Samson, 2006) compared different methods of estimating the canopy resistance above a wet sloping grassland and showed that Katerji and Perrier method (Katerji and Perrier, 1983) had better performance on estimating canopy resistance. In this study, we tried to use the same idea and compared six methods to estimate canopy resistance, which are the Jarvis type equation (Jarvis, 1976; Stewart, 1988), the Jarvis-Blanken and Black method (Blanken and Black, 2004), the Todorovic method (Todorovic, 1999), the Katerji and Perrier method, a new approach and constant canopy resistance. The study site was located in County Cork, southwest Ireland(51°〖59〗^' N 8°〖46〗^' W), and perennial ryegrass (Lolium perenne L.) was the dominant grass species in this area. An eddy covariance system was used to measure the latent heat flux above this humid grassland. The observed canopy resistance was calculated by rearranging the Penman-Monteith equation combined with the observed latent and sensible heat flux. Our results showed latent heat flux estimation as being less sensitive to the accuracy of canopy resistance predictions. We also found that the Katerji and Perrier method and the new approach have better performance than other methods in estimating the canopy resistance and latent heat flux.