A Systems Approach To Assess Trade Dependencies in U.S. Food–Energy–Water Nexus

We
present a network model of the United States (U.S.) interstate
food transfers to analyze the trade dependency with respect to participating
regions and embodied irrigation impacts from a food–energy–water
(FEW) nexus perspective. To this end, we utilize systems analysis
methods including the pointwise mutual information (PMI) measure to
provide an indication of interdependencies by estimating probability
of trade between states. PMI compares observed trade with a benchmark
of what is statistically expected given the structure and flow in
the network. This helps assess whether dependencies arising from empirically
observed trade occur due to chance or preferential attachment. The
implications of PMI values are demonstrated by using Texas as an example,
the largest importer in the U.S. grain transfer network. We find that
strong dependencies exist not only just with states (Kansas, Oklahoma,
Nebraska) providing high volume of transfer to Texas but also with
states that have comparatively lower trade (New Mexico). This is due
to New Mexico’s reliance on Texas as an important revenue source
compared to its other connections. For Texas, import interdependencies
arise from geographical proximity to trade. As these states primarily
rely on the commonly shared High Plains aquifer for irrigation, overreliance
poses a risk for water shortage for food supply in Texas. PMI values
also indicate the capacity to trade more (the states are less reliant
on each other than expected), and therefore provide an indication
of where the trade could be shifted to avoid groundwater scarcity.
However, some of the identified states rely on GHG emission intensive
fossil fuels such as diesel and gasoline for irrigation, highlighting
a potential tradeoff between crop water footprint and switching to
lower emissions pumping fuels.