Large-scale evaluation of the effects of adaptation to climate change by shifting transplanting date on rice production and quality in Japan

We evaluated the effect of projected increasing temperatures due to climate change on the yield and quality of rice, as well as the effectiveness of shifting the transplanting date as an adaptation measure, throughout Japan. As an indicator of rice quality, we adopted the heat stress index HD_m26, which is related to the decreased percentage of first grade rice due to high temperature, calculated as the cumulative temperature within 20 days after the heading date. We used a process-based rice growth model to assess the effect. We implemented the model for the period 1981-2100, and shifted the transplanting dates at 7-day intervals from -70 to +70 days from the standard transplanting date. The estimated yield was categorized into three classes with different degrees of quality degradation risk according to values of HD_ m26. Relative to the current transplanting date, nationwide total production was estimated to increase slightly in most climate change scenarios, although the proportion of production with quality degradation risk may increase with the rise in temperature. It may be possible to avoid this increased risk while maintaining total production by selecting an optimum transplanting date in consideration of both yield and quality. However, a large decrease in yield was found in some areas, suggesting that the current rice producing regions in Japan would become separated into suitable and unsuitable areas as temperatures increase.