The Canopy Conductance of a Humid Grassland

Abstract:

Penman-Monteith equation is widely used for estimating latent heat flux. The key parameter for implementing this equation is the canopy conductance (g_c). Recent research (Blaken and Black, 2004) showed that g_c could be well parameterized by a linear function of A_n/ (D₀* X₀^c), where A_n represents net assimilation, D₀ is leaf level saturation deficit, and X₀^c is CO₂ mole fraction. In this study, we tried to use the same idea for estimating g_cfor a humid grassland. The study site was located in County Cork, southwest Ireland (51^o59’’N 8^o46’’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 measured g_c was calculated by rearranging Penman-Monteith equation combined with the measured latent heat flux. Our data showed that the g_c decreased as the vapor pressure deficit and temperature increased. And it increased as the net radiation increased. Therefore, we found out that the best parameterization of g_c was a linear function of the product of the vapor deficit, temperature, and net radiation. Also, we used the g_c which was estimated by this linear function to predict the latent heat flux by Penman-Monteith equation and compared the predictions with those where the g_c was chosen to be a fixed value. Our analysis showed that this simple linear function for g_c can improve the latent heat flux predictions (R square increased from 0.48 to 0.66).