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

Hiroki Ikawa,Tsutomu Watanabe,Mayumi Yoshimoto,Tsuneo Kuwagata,Hidemitsu Sakai,Yasushi Ishigooka,Atsushi Maruyama,Minehiko Fukuoka,Charles P Chen,Shigenori Haginoya,Toshihiro Hasegawa,Sachinobu Ishida,Keisuke Ono

doi:10.1007/s10546-021-00604-6

Abstract

Known as the heat-mitigation effect, irrigated rice-paddy fields distribute a large fraction of their received energy to the latent heat during the growing season. The present hypothesis is that increased atmospheric CO2 concentration decreases the stomatal conductance of rice plants and increases the air temperature by means of an increased sensible heat flux. To test this hypothesis, a coupled regional atmospheric and crop energy-balance model is developed and applied to a 300 × 300 km2 region in Japan. Downscaling meteorological variables from grid-mean values of mixed land use (3 × 3 km2) generates realistic typical diurnal cycles of air temperature in rice paddies and adjacent residential areas. The model simulation shows that, on a typical sunny day in summer, doubling the CO2 concentration increases the daily maximum grid-mean air temperature, particularly where rice paddies are present, by up to 0.7 °C. This CO2 effect on the grid-mean air temperature is approximately half the effect of the reduction in rice-paddy area that is postulated to occur on a time scale similar to that of the atmospheric CO2 change. However, within the internal atmospheric boundary layer of the rice paddies, the CO2 effect on the air temperature (+ 0.44 °C) still exceeds the effects of the land-use change (+ 0.11 °C). These results show a potentially important interplay of plant physiological responses regarding atmospheric CO2 in the heat-mitigation effect of rice-paddy fields under a changing climate.

Highlights

The heat-mitigation effect of irrigated crop fields has been recognized for a long time (Holmes 1970)
The present study addresses the following specific research questions: (1) To what extent do the stomatal responses of rice plants to different levels of [CO2] affect the air temperature of rice-paddy areas in Japan? (2) How is the change in air temperature due to the stomatal response compared with the impact of land-use change? The objectives corresponding to these questions are (i) to couple a regional atmospheric model and a
The rice-crop energy model is coupled with the atmospheric model as follows: the atmospheric model uses the surface fluxes estimated by the rice-crop energy-balance model for the rice paddies, and the crop energy-balance model uses the meteorological variables estimated by the atmospheric model

Summary

Introduction

The heat-mitigation effect of irrigated crop fields has been recognized for a long time (Holmes 1970). In response to ongoing climate changes, an interest has emerged regarding whether and how this effect enhances or mitigates environmental changes (Dong et al 2016; Nocco et al 2019; Du et al 2019; Yang et al 2020). Rice paddies comprise the typical landscapes in many parts of eastern Asia, and their role in heat mitigation may be of interest. Recent studies have reported that changing the areal extents of rice paddies affects the regional climate (e.g., Dong et al 2016). To the best of our knowledge, no study has investigated how the heat-mitigation effect of rice paddies is altered by the physiological response of rice plants under a changing climate

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