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

Models for predicting hourly canopy resistance (rc) 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 rc was using an aerodynamic resistance (ra) and climatic resistance (r*), while another one was based on a relationship with solar radiation (SR). Nonlinear relationships between rc and r*, and between rc and SR were found for different growing stages of the rice crop. The constructed rc 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 rc 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 rc estimated using r* and SR, respectively. The rc integrated PM equation provided better performance than the bulk transfer equation. The results also revealed that neglecting the effect of ra on rc did not yield a significant difference in predicting LET.