Surface energy partitioning and evapotranspiration over a double-cropping paddy field in Bangladesh

The eddy covariance technique was used to measure surface energy balance and evapotranspiration in a double‐cropping paddy field in Mymensingh, northern Bangladesh (24·73°N, 90·42°E, 18 m above sea level). Because irrigation in dry season and frequent rainfall in the summer monsoon season kept the field flooded most of the year, most of the radiant energy was converted to latent heat flux except for the drained fallow period in winter. The ratio of the latent heat flux to the available energy, or evaporative fraction (EF), was 71–74% on average for two growing seasons and the flooded summer fallow period in rainy season. The evapotranspiration rate (ET) ranged from 0·2 to 6·6 mm d−1. The seasonal accumulated ET from transplanting to harvest in dry‐season rice (Boro rice) and wet‐season rice (Aman rice) was 370 and 307 mm with seasonal average of 3·3 and 2·9 mm d−1, respectively. In addition, 283 mm was lost as ET during the flooded summer fallow period, which characterized the seasonal variation of ET in this study site. The canopy conductance (Gc) showed a wide range from 1·0 to 20·2 mm s−1, but larger Gc values were found at higher leaf area index (LAI) periods for both Boro and Aman rice. Gc was closely related to the ratio of ET to equilibrium evaporation (Eeq), suggesting seasonal variability of ET is control by Eeq and Gc. Partitioning of ET by applying an empirical equation indicated that about 70 and 64% of seasonal ET came from transpiration in the Boro rice and the Aman rice, respectively. Copyright © 2011 John Wiley & Sons, Ltd.