Interregional Grain Flows and Carbon Responsibility in China: Two-Stage Network DEA and Allocation Optimization for Low-Carbon Agricultural Governance

Imagine a vast, interconnected system where food is grown in one place, shipped across hundreds of miles, and eaten in another. In this system, the environmental cost of growing that food—such as the carbon emissions from tractors and fertilizers—stays with the farm, but the benefit of the food ends up in a distant city. For decades, scientists and policymakers have struggled to measure who is truly responsible for the environmental impact of our food supply. Traditional methods often look at a single region in isolation, like a closed room, counting only the pollution generated within its borders. This approach creates a blind spot: it makes cities that import food look clean and efficient, while punishing the rural regions that grow the food for the rest of the country. As climate change forces us to rethink how we manage resources, understanding the hidden flow of environmental burdens between regions has become critical. If we cannot see the full picture of where emissions come from and where they go, we cannot design fair or effective strategies to reduce them.

A team of researchers from Hefei University of Technology and an Anhui investment firm has tackled this problem by developing a new way to map the journey of grain across China. They focused on the country's massive network of grain production and consumption, where some provinces grow far more than they need and ship the surplus to others. The researchers built a computational framework that treats the movement of grain not just as a trade transaction, but as a transfer of environmental responsibility. Instead of viewing each province as a separate island, their model connects the dots between the farm stage, where inputs like water, fertilizer, and machinery are used to grow crops, and the circulation stage, where that grain is transported and processed into food for consumers. By tracking the grain as it moves from surplus regions to deficit regions, the team could calculate how much of the carbon burden is shifted from the eater to the grower.

The study analyzed data from thirty Chinese provinces over five years, from 2017 to 2021. The researchers found a clear and often unfair split in the system. Provinces that export grain, such as those in the northeast and central plains, generally operate with high production efficiency. They use large, mechanized farms to grow massive amounts of food. However, because they are growing food for the entire nation, they also bear the brunt of the carbon emissions associated with cultivation. In contrast, provinces that import grain, often located along the wealthy eastern coast, appear to have very low local emissions because they do not grow much of their own food. Their local records show a clean environmental profile, but this is an illusion created by the fact that they have outsourced the dirty work of production to other regions. The researchers demonstrated that if these importing provinces were forced to grow all their own food without any help from neighbors, their local carbon emissions would skyrocket, revealing the true cost of their consumption.

To test how much this interregional trade actually changes the environmental picture, the researchers created a "what-if" scenario where grain could not move between provinces. In this closed-system simulation, they calculated what would happen if every province had to rely solely on its own land. The results were stark. Without the ability to ship grain from surplus to deficit areas, the carbon emissions from farming in importing regions would jump dramatically. For example, the study noted that a major importing province like Beijing would see its agricultural carbon emissions rise to roughly twenty-six times their current level if it had to produce all its own grain. Conversely, the exporting regions would see their emissions drop significantly, as they would no longer be growing food for distant cities. This comparison proved that the current system of moving grain actually helps lower the total amount of carbon emitted by farming across the country, but it does so by concentrating the burden on the producing regions.

The researchers then asked a more practical question: if we must keep the total amount of grain produced for the nation exactly the same, can we rearrange who grows what to reduce emissions even further? They used their model to simulate shifting production responsibilities among the provinces that already export grain. The goal was to move more of the growing to the most efficient regions and less to the less efficient ones, without changing the total food supply. The simulation showed that this kind of strategic reallocation could reduce national cultivation-related carbon emissions by nearly 5 percent. Specifically, the total emissions from farming could drop from 55.65 million tons to 52.91 million tons. This reduction would be achieved by directing more production to provinces with large, contiguous farmland and advanced machinery, which can grow grain with less carbon per ton, while asking provinces with fragmented land or higher costs to grow slightly less.

The study also looked at what drives these differences in efficiency. They found that regions with a higher proportion of grain crops and more urbanization tended to be more efficient, likely because of better access to technology and markets. However, they also found that strict environmental protections, such as large nature reserves, sometimes made it harder to achieve high efficiency scores. This is because farmers in these areas are forced to grow food on less suitable land, requiring more fertilizer and water to get the same yield. The researchers concluded that a one-size-fits-all approach to environmental policy will not work. A province that imports food faces different challenges than one that exports it. Importing regions need to focus on logistics and reducing waste in the supply chain, while exporting regions need support to improve their farming techniques and manage the heavy environmental load they carry for the rest of the country.

Ultimately, this research offers a new way to think about fairness in climate governance. It suggests that we cannot simply look at a map of emissions and assume the numbers tell the whole story. The responsibility for the carbon footprint of our food is shared across the network of production and consumption. The study proposes that policies should reflect this reality by creating accounting systems that recognize the burden placed on exporting regions. It suggests that regions benefiting from grain imports should contribute to the environmental costs of the regions that grow their food. By understanding these hidden flows, policymakers can design better strategies that reduce emissions without compromising the food supply, ensuring that the cost of feeding the nation is shared more equitably and effectively.