An impact evaluation of global warming on market arrival based on the identification of production situations for major open-field vegetables in Japan

We assessed the impact of global warming on the production of major open-field vegetables, based on the daily mean temperature on average over 20-year periods, using the results of Ohara et al. (2020), which identified the production situation of major open-field vegetables (in season), by former municipality (based on the Agriculture and Forestry Census), over a roughly 10-day period. Compared to the period from 1981 to 2000, the yearly mean temperature in Japan will be 0.5 to 1.5°C higher from 2026 to 2045, and 0.8 to 2.7°C higher from 2046 to 2065, based on the Model for Interdisciplinary Research on Climate Version Five (MIROC5) RCP 8.5. As temperatures rise, cultivation and harvest periods are typically shortened. Therefore, if the beginning of planting season remains unchanged, times and quantities of market arrival of the vegetables will be significantly altered. Winter harvesting periods will begin earlier, and become more concentrated. Total harvest area will increase between November and December, decrease between February and March, and experience decreases during the transitions between hot and cool season production periods. Planting frequency during cultivation periods can dramatically impact the total harvested area, with planting frequency being inversely correlated with impact. Thus far, cooperation has enabled production areas to successfully adapt to seasonal climate changes; however, these efforts are unlikely to remain successful in the face of future temperature increases due to global warming. In the near future, it is improbable that the daily mean temperature on average over 20-year periods in Japan will significantly exceed the preferred range for cultivation. However, annual temperature fluctuation is already significant (in Japan, the annual fluctuation of monthly mean temperatures from 1981 and 2000 was 1.0 to 1.4°C [RMS value]), and its impact may exceed that of global warming; therefore, careful attention must be paid to such fluctuation.