87th AMS Annual Meeting

Monday, 15 January 2007
Dynamic vegetation model for the descriptions of evapotranspiration and photosynthetic carbon sink observed at a rice paddy
Exhibit Hall C (Henry B. Gonzalez Convention Center)
Jeng-Lin Tsai, National Chung Hsing University, Taichung, Taiwan; and B. J. Tsuang
Rice is the major staple in the monsoon Asia. It is grown under irrigation. More than 80 % of freshwater resources development projects in Asia are used for irrigation and about half of the total irrigation water is used for rice production. The water-fed rice paddy field may modify the surface energy budget, water cycle, runoff and ground water storage of the region. The observations by an eddy covariance (EC) system suggest that Bowen ratio was about 0.16 during the daylight hours from a rice paddy. That is, the daytime surface latent heat flux was about 6 times larger than the surface sensible heat flux. The EC system also measured absorbed CO2 flux. The equivalent photosynthetic energy flux was about 2 % of net solar radiation. The diurnal pattern of the canopy resistance for evapotranspiration of the rice paddy is found to be a U shape with the minimum value at 42 s m-1 around noon. Two state-of-the-art evapotranspiration schemes are used to simulate the evapotranspiration rate observed at the rice paddy in Taiwan. Both schemes fail to reproduce evapotranspiration rates under the conditions of incoming solar radiation greater than 800 W m-2. It is found that although evapotranspiration and photosynthetic carbon sink increased with incoming solar radiation while the radiation was < 800 W m-2, the stomata partly closed itself for preventing excess evapotranspiration while the radiation was > 800 W m-2. A better description of the relationship of the interaction between vegetation and the atmosphere is needed under strong solar radiation.

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