Probabilistic risk assessment of the rice cropping schedule for central Hokkaido, Japan

A framework for the probabilistic risk assessment of the rice (Oryza sativa L.) cropping schedule (PRARCS) is presented. The method accounts for interannual meteorological variation, as opposed to the traditional cultivation schedule planning method, which is based on the seasonal change in long-term average air temperature. PRARCS uses an arbitrary developmental index model to estimate the timing of the heading stage, which is required to assess the risks of cold or heat damage and productivity. All results of risk assessment and productivity are linked to transplanting date as the most important cultivation practice for irrigated rice paddies. The results of assessments using PRARCS at Iwamizawa, central Hokkaido, Japan, indicated that for the current climate the optimal transplanting period is the end of May, and this corresponds to the actual transplanting dates used and the increasing risks and decreasing productivity with earlier or later transplanting. Assessment using projected climatic data for the period 2031-50 showed that Akitakomachi and Hitomebore, present-day cultivars in the Tohoku region, could achieve satisfactory productivity in central Hokkaido. For the term 2081-2100, assessment using an extreme warming projection (4.7°C higher than at present) indicated that the probability of heat damage (whitebased rice and heat sterility) is once every 2 yr for some transplanting dates and that cold risks (transplanting damage, cold injury, and immature ripening) are reduced. It was also found that the cultivar Koshihikari, at present suited to more southern regions, could be cultivated in central Hokkaido in 2081- 2100 if transplanting is conducted in early May.