Parameterization of canopy resistance for modeling the energy partitioning of a paddy rice field

Models for predicting hourly canopy resistance (r_c) and latent heat flux (LET) based on the Penman–Monteith (PM) and bulk transfer methods are presented. The micrometeorological data and LET were observed during paddy rice-growing seasons in 2010 in Japan. One approach to model r_c was using an aerodynamic resistance (r_a) and climatic resistance (r^*), while another one was based on a relationship with solar radiation (SR). Nonlinear relationships between r_c and r^*, and between r_c and SR were found for different growing stages of the rice crop. The constructed r_c models were integrated to the PM and bulk transfer methods and compared with measured LET using a Bowen ratio–energy balance method. The root mean square errors (RMSEs) were 155.2 and 170.5 W m⁻² for the bulk transfer method with r_c estimated using r^* and with a function of SR, respectively, while the RMSEs were 87.4 and 85.7 W m⁻² for the PM method with r_c estimated using r^* and SR, respectively. The r_c integrated PM equation provided better performance than the bulk transfer equation. The results also revealed that neglecting the effect of r_a on r_c did not yield a significant difference in predicting LET.