Climate-induced risk assessment of future rice production value in the Tohoku and Kyushu regions, Japan

Abstract

　Climate change is increasingly being recognized as a potential threat to food security. This study assessed the risk of climate change on rice production value in the Tohoku and Kyushu regions. In a scenario without climate change mitigation, characterized by a 4 K global average temperature increase compared to pre-industrial levels, a significant decrease in rice production value was projected for Tohoku (93.9%) and Kyushu (75.9%). Based on the current value, each 1 K increase in temperature is estimated to result in an annual economic loss of approximately 7 and 12 billion yen in Tohoku and Kyushu, respectively. The frequency of losses in production value, which is typically expected to occur once every 25 years under current climate conditions, may occur more frequently (Tohoku: every 4.0 years; Kyushu every 1.1 years). This increased risk is attributed to a reduction in the proportion of first-grade rice, which is compounded by decreased yields in Kyushu. The negative trends become less pronounced when considering the mitigation efforts that limit the global temperature rise to 2 K. In this scenario, the decline in production value that occurs once every 25 years does not occur in Tohoku because of increased yields. In Kyushu, however, this decline still occurs once every 5.6 years, mainly because of a reduced proportion of first-grade rice in the total production. In both regions, increasing yield through earlier transplanting proved more effective in mitigating production decline than improving the proportion of first-grade rice through later transplanting, regardless of the extent of the temperature rise. With the current rice varieties and transplanting schedules, production decline is difficult to prevent under severe climate change conditions. Therefore, high-temperature-tolerant rice varieties must be promoted, and their transplantation must be adjusted to adapt to future environmental conditions.