2011 Volume 67 Issue 3 Pages 89-97
In order to quantify evaportranspiration and separate it into evaporation and transpiration, the two-layer model was applied. The aerodynamic and rice canopy resistance were estimated based on the two-layer model with measured meteorological data, water surface evaporation beneath the rice canopy and transpiration from the canopy measured by lysimeters. The aerodynamic resistances included aerodynamic resistance between the rice canopy and the air (rac), aerodynamic resistance between the water surface beneath the rice canopy and the air (rag), and the total aerodynamic resistance (ra). It was found that the aerodynamic resistances decreased with the increase in wind speed, while they increased with the increase in plant height. The relationships between these aerodynamic resistances and the wind speed above the canopy were individually parameterized by plant height. The rice canopy resistance (rc) was mainly influenced by the global solar radiation (SR) and the vapor pressure deficit of the air (VPD). The rc decreased with the increase in SR, while it increased with the increase in the VPD. The rc model was developed by a hyperbolic function with SR for the three growing stages and the model parameter was decided by the VPD. By incorporating these resistance sub-models into the two-layer model, evaporation from the water surface beneath the canopy and transpiration by the rice canopy were reproduced successfully.
