Abstract
In Hokkaido, in northern Japan, rice yields are frequently affected by cool summers in the present climate. Recently, several studies have noted the possibility that cool summer damage may not be reduced even with global warming due to earlier rice phenology. We examined the changes in the range of rice sterility associated with rising temperatures focusing on inter-annual variation in temperature. By raising daily mean and daily maximum temperatures uniformly, we calculated the sterility rate of the Kirara397 variety locally planted in Hokkaido. Generally, long-term mean rice sterility decreases with rising temperatures. However, in each year and with each transplanting date, rice sterility remains identical to the present or even worsens in some cases. We called those cases “accelerated cool summer damage” (ACSD). In the cases of rising temperature, the growth rate is accelerated, and the period of vulnerability to low temperatures become earlier. When the temperature during the earlier period of vulnerability is equal to or less than that during the original period of vulnerability in the present, ACSD occurs. Future rice sterility that induces cool summer damage may remain even if the temperatures rise associated with global warming, since the increase in temperature during the period of vulnerability is smaller than the range of inter-annual variation in temperature. We also found that there is a possibility that extremely high rice sterility is increased in a warmer climate if the range of inter-annual variation in temperature expands. This finding suggests that rice sterility may be increased by the inter-annual variation in temperature, even if the long-term mean sterility decreases as the temperature rises.