Estimating the Water Temperature of Paddy Fields under Abnormal Weather Conditions using an Equilibrium Water Temperature Model

Abstract

A simple model to estimate the daily mean water temperature of paddy fields from observed meteorological data was developed. The model is based on a crop growth model coupled to an equilibrium water temperature model. Using this model, the water temperature of a paddy field can be estimated from only three factors namely, air temperature, solar radiation, and water vapor pressure, observed a nearby weather station. Validity of the model was examined on actual paddy fields of different style of cultivation, under warm temperate climate. There was a good agreement between observed and calculated temperature. This suggests that the water temperature of paddy fields can be estimated well using this model without any correction to adjust for the style of cultivation. The model was applied to estimate the water temperature of paddy fields under normal and abnormal weather conditions. Under normal weather conditions, there were regional differences in water temperature of paddy fields caused by the differences in elevation and cultivation period of paddy fields. Under abnormal weather conditions, the deviation from normal of water temperature was directly proportional to the deviation from normal of air temperature. A 1.0°C decrease in air temperature during a cool summer year corresponded to a 1.0°C decrease in water temperature of paddy fields, whereas a 1.0°C increase in air temperature during a hot summer year corresponded to a 0.6°C increase in water temperature of paddy fields. © 1998, The Society of Agricultural Meteorology of Japan. All rights reserved.