The fragility of the United States food supply chain multilayer network

Abstract:

In a national economic system, supply chains form a spatial network of interactions among suppliers and demanders of commodities in different geographic locations. Shocks -sudden disturbances- to the supply or demand for a certain commodity can lead to shortages of that commodity or others that depend on it to be produced. Given the highly connected nature of supply chain networks, shocks that originate in a geographic region can be transferred to others following trade linkages. Here, we analyze the exposure and fragility of United States (US) cities and food sectors to domestic supply shocks. To characterize the supply chain network for different food products we use a multiregional input-output dataset of the US economy. The supply chain network is represented as multilayer network where nodes are geographic regions, layers are economic sectors and links are economic transactions between regions and sectors. Together with a network cascade model, the multilayer network is used to explore the propagation of economic shocks along domestic supply chains. Our results show that the magnitude and spread of the shock varies widely depending on the origin (geographic location and economic sector) of the shock. The response of supply chains to shocks reveals a threshold-like behavior, where, below a certain failure level, the avalanche size increases rapidly for any node in the network. We find that the most fragile regions tend to be in the central United States, which are regions that specialize in food production and manufacturing. The fragility risk, measured by the intersection of the fragility level of a node and its exposure to shocks, varies across regions and sectors. This suggests that interventions aiming to make the supply-chain network more robust to shocks are likely needed at multiple levels of network aggregation.