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

Abstract

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.

Transcriptomic Changes in Hot Spring Frog Tadpoles (Buergeria otai) in Response to Heat Stress

“…Thus, the mechanisms identified in this study were not evolutionarily acquired in Buergeria lineages. Many anuran species lay eggs in temporally formed shallow water pools, such as paddy fields, whereby water temperatures can reach 36 • C (Maruyama et al, 2017). Therefore, although the present study employed rapid and acute heat stress and did not take into account acclimation effects that may occur in the field, a wide range of anuran species may have a similar transcriptomic response to heat stress as that observed in B. otai tadpoles.…”

Heat-Mitigation Effects of Irrigated Rice-Paddy Fields Under Changing Atmospheric Carbon Dioxide Based on a Coupled Atmosphere and Crop Energy-Balance Model

“…The rice-crop energy-balance model is based on the model of Ikawa et al (2018), which comprises an energy-balance submodel (Watanabe 1994;Maruyama and Kuwagata 2010;Maruyama et al 2017) and a canopy-photosynthesis submodel (de Pury and Farquhar 1997). The energy fluxes are calculated based on a so-called double-source model.…”

Interpretable Framework of Physics‐Guided Neural Network With Attention Mechanism: Simulating Paddy Field Water Temperature Variations

“…It is necessary to accurately understand and predict the temperature environment in the paddy field and develop water‐management measures to maximize land productivity under limited natural and human resources. For water temperature modeling in paddy fields, some researchers proposed physical process models to simulate the daily dynamics of water temperature while considering the effects of vegetation layers (Maruyama & Kuwagata, 2010; Maruyama et al., 2017; Smesrud et al., 2014; Watanabe et al., 2004; Yoshida et al., 2013). Physical process models are based on specific physical theories or the integration thereof to elucidate causal relationships between interventions and outcomes.…”