As a vital part of sustainable development, food security is challenged by prolonged and concurrent pressures. Efforts have long been devoted to balance grain production across China as a whole, and thereby the uncertainties and underlying crisis in the regional grain-producing systems are hidden. In this study, we characterize the dynamic evolution of 357 cities and explore the dominant supply and demand effects to signal early warnings of grain insecurity. Our results show that 220 cities are in unsustainable grain supply–demand conditions in comparison with 10 years ago. Additionally, the south and southwest of China have experienced enlarged disparities and more severe grain insecurity. The dual effects from both increased population and decreased grain output are substantially responsible for the unsustainable grain-producing system on the city scale. Moreover, cities identified as having grain insecurity occupy high-quality cultivated land, including 55.4% of top-grade land, 49.8% of high-grade land, and only 28.9% of low-grade land. We consequently inform the incongruity between grain productivity and regional grain conditions. It is suggested that current intensive management of cultivation and the strategy of differentiated responsibilities in grain production should be based on environmental sustainability and a degree of self-sufficiency across the region.

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