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.

灌溉稻田被称为散热效应，在生长季节将其接收到的能量的很大一部分分配给潜热。目前的假设是，大气中CO ₂浓度的增加会降低水稻植物的气孔导度，并通过增加显热通量来提高气温。为了验证这一假设，开发了区域大气和作物能量平衡的耦合模型，并将其应用于日本的300×300 km ²区域。从混合土地利用的网格均值（3×3 km ²）在稻田和邻近居民区中产生逼真的，典型的气温昼夜循环。模型仿真表明，在夏季的典型晴天，将CO ₂浓度增加一倍可使每日最大电网平均气温（尤其是存在稻田的地方）的最高气温升高0.7°C。CO ₂对电网平均空气温度的影响大约是稻米面积减少的影响的一半，而稻米面积减少的假设是在类似于大气CO ₂变化的时间尺度上发生的。然而，在稻田的内部大气边界层中，CO ₂对空气温度的影响（+ 0.44°C）仍然超过了土地利用变化的影响（+ 0.11°C）。这些结果表明，在气候变化的稻田减热效应中，有关大气CO ₂的植物生理反应之间可能存在重要的相互作用。