Rice quality, which is intricately connected to market value and human nutrition, is sensitive to weather conditions. However, the relative importance of the different climatic factors is poorly understood, and the impact of climate change on rice quality has been little studied on a large scale. Here, using more than 35 years of rice quality data, we present the first effort to determine the key climate variables driving rice quality in China and Japan. Results show a significant decline in high quality rice rate (HRR, an indicator of rice quality), mainly driven by warm nighttime temperatures when they exceed a critical threshold estimated at 18°C and 12°C in China and Japan, respectively. Climate projections suggest a continuing decreasing trend in HRR under moderate and high emission scenarios by 2100. These findings emphasize the importance of breeding new heat tolerant cultivars to maintain stable rice quality in the future.

Plain Language Summary Food security is not only related to yield, but also to quality, which is closely related to human nutrition and market value. Although crop quality is generally controlled by breed genes, climate change also has an important impact. Unfortunately, existing studies on the impact of climate change on rice quality mostly performed at sites scale, the knowledge on a large scale such as the global or national scale is still limited. This is partly related to the incompleteness of relevant data, and also it is related to the current focus primarily on yield and neglect of quality. Our findings highlight that food security should consider both yield and quality aspects.