Modeling water temperature of Hungarian rice fields

Low temperature during the sensitive phenophases of rice (Oryza sativa L.) can cause spikelet sterility. In Hungary this is one of the main weather and climatic risks resulting in yield loss. The thermal characteristics and heat balance of flooding water are very different from that of the air. Therefore, the modifying of water level gives an effective tool for rice growers to reduce cold stress. To help this and also to improve weather-rice models it is essential to predict water temperature from standard meteorological data. Two empirical models were established based on water temperature measurements in a representative Hungarian rice field during the reproductive and early ripening stages from mid-July till the beginning of September in 2006 (model construction) and 2005 (model verification). Both models proved an efficient and accurate tool in simulating daily minimum, maximum, and average of flooding water temperature. The error in prediction is negligible from a practical point of view, especially if compared to the large differences between the extremes of air and water temperature.