Prediction of the Influence of Global Warming on Rice Growth in the 2030s in Hokkaido, the Coldest Region in Japan and the Measures to Be Taken for Sustained Production

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Prediction of the Influence of Global Warming on Rice Growth in the 2030s in Hokkaido, the Coldest Region in Japan and the Measures to Be Taken for Sustained Production

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Abstract:

The mean air temperature from May to September, during which the rice plant is cultured in the paddy field in Hokkaido, has increased during the four decades from 1980 to 2019. The growth of rice in the 2030s in comparison to the most recent decade (2010—2019) was predicted using two predicted weathers for the 2030s and the previously reported relational expression. In the 2030s, the critical planting date (early limit of planting day) will be 8~9 days earlier than that in the 2010s. The early limit of heading date will also be 1~5 days earlier, and the late limit of heading date will be 1~5 days later. Therefore, the safe heading period will be 2~10 days longer and the heading date will be 1~3 days earlier. As the period between heading date and late limit of heading will be 2~9 days longer, cool summer damage due to delayed growth will decrease slightly. Concerning the weather at different growth stages, the average air temperature will be the same or lower for the earlier growth during the 30 days after 24 days before heading. During the 40 days after 10 days before heading and during the 40 days after heading, the average air temperature will be slightly higher, and the amount of solar radiation will be slightly lower. Then the grain yield will be slightly lower (96％~98％), and the agroclimatic index for expressing the potential of grain yield will be the same. As the average air temperature during the critical stage of chilling injury at the booting stage, which is related with occurrence of male sterility, will be slightly lower or the same, the risk of occurrence of cool weather damage will remain. On the other hand, the appearance frequency of low temperature, which causes sterility, will vary depending on the area. The protein content of milled rice will be the same and the amylose content will be slightly lower. Therefore, the palatability will be slightly better. On the appearance quality of rice grain, there will be no consistent tendency between the 2030s and the 2010s in the percentages of damaged grain and of colored grain, and the percentage of immature grain will be slightly higher. Although the whiteness of milled rice will be the same, the whiteness of brown rice will be slightly higher. The measures to be taken in response to the above predictions are discussed.

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