Estimating Rice Transplanting Dates and Projected Shifts under Climate Change in Japan with the Use of Sentinel‐1 Imagery and CMIP6 Scenarios

ABSTRACT This study examines the impact of climate change on rice transplanting timings in Japan, focusing on Hyogo and Niigata Prefectures. Using time‐series Sentinel‐1 SAR imagery, we identified transplanting dates based on the sharp decrease in backscatter coefficients during the ponding period. The estimation was validated against survey data from agricultural corporations and cooperatives, yielding a Root Mean Square Error (RMSE) of 9.8 days for Hyogo and 6.2 days for Niigata. Current trends reflect regional variations due to climate and social practices, such as intensive planting during Japan's Golden Week holidays. Projections under the CMIP6 RCP 8.5 scenario indicate significant delay in future transplanting dates, averaging 35 days in Hyogo and 74 days in Niigata by the end of the 21st century. These delays are more pronounced in higher‐elevation and colder regions. This integrated approach offers valuable insights into the potential for adjusting transplanting schedules to mitigate the impacts of climate change.