Improving estimates of subnational commodity flows in LCA for policy support: A US case study

Life cycle assessment models incorporating interregional commodity flows at subnational levels can be used to estimate regional implications of environmental and energy policies, and to evaluate corporate's regional supply-chain sustainability impacts. Here, I study the importance of subnational commodity flows in life cycle inventory results of US products. Two models are used for analysis, an aggregate input-output model covering all productive sectors and a detailed process model focusing on corn. On average, ~50% of agricultural, mining, and manufacturing goods traveled across state boundaries (10-50% for corn specifically). Neglecting the inter-state commodity flows can lead to large errors in state-level life cycle inventory results (up to 200-400%). It can also affect national average inventory results: depending on where corn is sourced from, an average unit of corn used as feed and feedstock in the US could have substantially different amounts of embodied water. Results further suggest that the more spatially variable of an environmental stressor, water use the more important it is to account for commodity flows. A better understanding of interregional commodity flows at subnational levels improves the predictive capability of life cycle models for better policy support.