A Water Temperature Simulation Model for Rice Paddies With Variable Water Depths

• Published in: Water resources research 2017-12, Vol.53 (12), p.10065-10084
• Main Authors: Maruyama, Atsushi, Nemoto, Manabu, Hamasaki, Takahiro, Ishida, Sachinobu, Kuwagata, Tsuneo
• Format: Article
• Language: English
• Subjects: Aerodynamic properties; Air temperature; Computer simulation; Convection; Convection modes; Energy balance; Field tests; Free convection; Greenhouse effect; Greenhouse gases; Growing season; Heat exchange; Irrigation; Irrigation water; Leaf area; Leaf area index; Low temperature; Mathematical models; Oryza; Plant growth; Rice; Rice fields; Simulation; Surface roughness; Temperature differences; Temperature effects; Water depth; Water management; Water temperature
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1002/2017WR021019

A water temperature simulation model was developed to estimate the effects of water management on the thermal environment in rice paddies. The model was based on two energy balance equations: for the ground and for the vegetation, and considered the water layer and changes in the aerodynamic properties of its surface with water depth. The model was examined with field experiments for water depths of 0 mm (drained conditions) and 100 mm (flooded condition) at two locations. Daily mean water temperatures in the flooded condition were mostly higher than in the drained condition in both locations, and the maximum difference reached 2.6°C. This difference was mainly caused by the difference in surface roughness of the ground. Heat exchange by free convection played an important role in determining water temperature. From the model simulation, the temperature difference between drained and flooded conditions was more apparent under low air temperature and small leaf area index conditions; the maximum difference reached 3°C. Most of this difference occurred when the range of water depth was lower than 50 mm. The season‐long variation in modeled water temperature showed good agreement with an observation data set from rice paddies with various rice‐growing seasons, for a diverse range of water depths (root mean square error of 0.8–1.0°C). The proposed model can estimate water temperature for a given water depth, irrigation, and drainage conditions, which will improve our understanding of the effect of water management on plant growth and greenhouse gas emissions through the thermal environment of rice paddies. A model was developed to estimate the effects of water management on paddy water temperature The surface roughness of the ground in the rice paddies strongly affects water temperature The model simulates water temperature accurately considering the change in surface roughness with variable water depth