In the Kyushu region of Japan, the occurrence of chalky rice grains caused by high air temperatures is a concern for a major local cultivar, Hinohikari. To avoid heat stress, a cultivar shift to Nikomaru, which is highly tolerant to high temperatures, is expected in this region. However, it is unknown how effective the shifting cultivar is for avoiding the heat‑induced chalky grains under possible high air temperature in the future. Therefore, in the present study, we aimed to simulate the impacts of increased air temperature on chalky grains in Hinohikari and Nikomaru based on 10 future climate scenarios, derived from a combination of five general circulation models and two representative concentration pathway (RCP) scenarios. Under RCP2.6 and RCP8.5, the median percentages of chalky grains in Hinohikari averaged over the entire Kyushu region were 29.6% and 42.8% in 2041‑2060 and 31.4% and 83.6% in 2081‑2100, respectively. While the cultivar shift to Nikomaru reduced them by approximately 20‑30%, the damage could not be reduced to below approximately 10% under RCP8.5. Furthermore, we tested the effects of other adaptation options: late transplanting. Although implementing both adaptation options, a cultivar shift and late transplanting, was somewhat effective in the middle of the 21st century, it could not suppress the heat‑induced incidence of chalky rice grains in 2081‑2100 under RCP8.5. Therefore, other adaptation options and mitigation measures may be needed in the end of the 21st century under possible high air temperatures.