Effect of convection in ponded water on the thermal regime of a paddy field

Flooded conditions in a lowland paddy field provide a unique condition critical to the growth and development of rice plants, particularly their early growth. In order to illustrate the phenomena of a surface water layer on the thermal regime, a vertical temperature profile was measured in the paddy field, and the results were confirmed with model simulations under infrared and solar radiation, which were regarded as non-convective and convective systems, respectively. The results show that solar radiation is absorbed at the soil surface and heat energy is transferred to the overlying water layer by convection and to the underlying soil by conduction. Convection continues even at night as a result of the temperature differences between the boundaries of the water layer. Convection in the water layer plays an important role in defining the thermal regime of a paddy field. (author)