2021 年 77 巻 2 号 p. 139-149
Rice is the most important cereal crop in Japan, and therefore the impact of projected climate change on its production and quality has been assessed using rice growth models accounting for the effects of rising temperature and atmospheric CO2 concentration ([CO2]) on important growth processes. Recent experimental studies, however, have shown some negative effects of interactions between [CO2] and temperature on yield and quality of rice which were not accounted for by previous impact assessments. This study examined the importance of [CO2]×temperature interactions in the nationwide impacts of climate change on grain yield and quality of rice in Japan by 2100. We introduced new functions accounting for the effects of interactions on yield. Then we adopted the acceleration by elevated [CO2] in the estimation of the occurrence of chalky grains, an indicator of appearance quality of rice. We applied the modified model to Japan at a spatial resolution of 1 km using 10 climate scenarios (5 Global Circulation Models×2 representative concentration pathways [RCPs]) from 1981 to 2100. The effects of the newly introduced negative effects of [CO2]×temperature were evaluated by comparing simulations with and without the interaction in each scenario. Nationwide production was estimated to decrease by up to 28% and the percentage of white chalky grains to increase up to 16% relative to the previous assessment results, especially in RCP8.5, in which larger increases were projected in both temperature and [CO2]. The result suggests that the positive effect of elevated [CO2], which had been expected to offset the negative effect of increased temperature on rice productivity, may be limited in the future, and rice quality degradation may be more severe than predicted previously.