Heavy rainfall leading to disasters is projected to intensify and become more frequent as the average global temperature continues to rise. We have estimated the ratio of the intensity of heavy rainfall in the future to that in the past (hereinafter referred to as “rainfall change rate”), using large-ensemble climate model predictions. The results show that the average rainfall change rate across Japan is 1.1, with an increase in temperature of 2 °C. The rate is higher in the northern Japan.