Surface energy components, CO2 flux and canopy resistance from a rice paddy in Taiwan

A field experiment was conducted to study surface energy budget and CO2 flux of rice paddies in Taiwan. During the daytime, the energy balance ratio (the ratio between the sum of turbulence heat fluxes measured by an Eddy Covariance (EC) system and the available energy) is found to be 0.9. To examine which turbulent heat flux component was underestimated, a tethersonde balloon was launched to examine the Bowen ratio measured by the EC system and by the tethersonde system. Both systems suggest the ratio was about 0.16 during the daytime. That is, the daytime latent heat flux is about 6 times larger than the sensible heat flux from a rice paddy. To close the energy budget, the imbalance heat flux is proportionally redistributed to latent heat flux and sensible heat flux according to the Bowen ratio measured by the EC system. The EC system also measured the daytime absorbed CO2 flux at 1.1 mg m-2 s-1 and nighttime respiration rate at 0.11 mg m-2 s-1. The equivalent photosynthetic energy flux was 1 % of net solar radiation. The amount of accumulated carbon storage in the rice paddy based on the flux measurement is almost the same as that measured by the mass budget method. Using the corrected latent heat flux, the diurnal pattern of the canopy resistance for evapotranspiration is found to be a U shape with the minimum value at 42 s m-1 around noon of the rice paddy. In addition, an evapotranspiration scheme is tested at the site. It is found that the evapotranspiration rate observed at the study site is much higher than the transpiration rate estimated according to a scheme used in a state-of-art climate model. It implies that evaporation from the rice paddy should not be neglected.