Modeling water temperature in a rice paddy for agro-environmental research

Water temperature in rice paddies (Oryza sativa L.) is one of the most important factors affecting the growth and yield of rice, and also influences CH4 emission from paddy fields. We developed a simple model of the daily mean water temperature in a rice paddy. The model has two steps for evaluating the paddy water temperature. In the first step, the daily mean water temperature of a non-vegetated water surface (View the MathML source) is evaluated from meteorological data (air temperature, specific humidity, wind speed, solar radiation, and downward longwave radiation) by daily 24-h mean or daytime (nighttime) 12-h mean heat balance equations. The bulk heat transfer coefficient at the water surface is a key parameter for evaluating View the MathML source. Next, the daily mean water temperature in a rice paddy View the MathML source is evaluated by adding a correction term to View the MathML source. Here, the correction term is described as a function of the leaf area index (LAI), solar radiation, and wind speed, and the formula was determined empirically. The model simulated fairly well the daily mean water temperature of rice paddies with root mean square errors of 0.81–0.85 °C.