Cities are a basic unit of civilization. Cities like Rome, Jerusalem, and Beijing have anchored their civilizations for thousands of years by adapting and thriving despite sweeping changes in climate, politics, religion, and technology. Other cities like Detroit are younger and are now facing their first real tests. A resilient city can resist and recover from large disruptions. As we look ahead into a dynamic and uncertain 21st century, building resilience into our cities and our civilization is a compelling challenge for science and policy. But what makes a city resilient, and how can policy drive resilience by design?
Engineers like me are trained to design reliable systems and machines that avoid and recover from failures. We harden systems against threats to prevent failure, and we design in redundancy - like an emergency brake on a car. An engineer would normally need accurate data on the threat- that is, a good prediction- to create an efficient design. But the world is a complex place where we never know what’s coming at us tomorrow (COVID-19, anyone?). How can we engineer cities that are resilient to “Black Swan” shocks that we can’t see coming?
Moreover, our cities and their economies weren’t exactly engineered; they grew and evolved over time, like a natural ecosystem. In 1973, ecologist C.S. Holling developed the theory that diversity helps ecosystems achieve resilience to shocks by boosting their adaptive capacity. This idea makes sense; if an ecosystem has many different sources of energy, water, and nutrients, and many different species, it has more chances to successfully adapt to a new equilibrium after a disruption. Diversity is a broadly successful resilience strategy that works for all hazards, including shocks we don’t see coming.
If a city is an ecosystem, then supply chains are a city’s food web. Supply chains are the complicated networks of contracts, payments, warehouses, factories, farms, trucks, trains, power lines, pipelines, etc. that make the economy hum. Critical supply chains, like water, power, fuel, medical, and telecom, provide “life or death” services that a city can’t live without for even a short time. Shocks to critical supply chains are a serious threat. In the past year we’ve seen just how easily a city’s critical supply chains can be shocked. 2021 has been a banner year for supply chain shocks like the global COVID-19 supply chain crunch, the Colonial Pipeline and JBS meat processing ransomware attacks, the Suez Canal blockage, the hack of water supplies in Florida, and the ERCOT power and water outage. Historical examples of critical supply chain shock include the 1973 oil embargos by OPEC against the U.S., the 1941 Embargo Act where the U.S. cut off oil to Japan, and the 2010-2012 world food price crisis.
After assembling a history of food flow data for U.S. cities, Gomez et al. (2021) test the hypothesis that the diversity of a city’s food supply chain explains the resilience of the city’s food supply to shocks. It turns out that the ecological food web analogy holds very well. The diversity of a city’s supply chain explains over 90% of the intensity, duration, and frequency of historically observed food supply shocks. Remarkably, this model works regardless of the cause of the shock; it could be a drought affecting the city’s farm suppliers, the failure of a grocery business in the city, or an international conflict. This finding is both profound and practical. We now have a simple and effective mathematical basis for policies to boost a city’s supply chain resilience. Coming years will reveal how broadly this finding holds for other kinds of supply chains. Does it hold for households? Nations? Electricity? Telecommunications?
This math is useful for businesses that operate critical supply chains, government regulators who need to control risk in critical systems, emergency managers who need to prioritize resources, and insurers who set premiums. This finding is also a promising “win” for the intellectual synthesis of data science, network theory, and ecologically-inspired (or nature-based) resilience thinking, and argues for further investment in the basic research that led to this practical breakthrough. I believe this math and method can underpin a new class of federal regulations for critical supply chain security, and can be used to make our economy more secure and resilient. We’re excited to see where these ideas take us in coming years. Resilience, based on solid science, is excellent policy for an unpredictable 21st century.
TO LEARN MORE
Educational materials on supply chains, including the FEW-View visualizer that shows supply chain resilience for all US cities, are available at https://fewsion.us
Episode Seven of the Crucial FEWSION podcast series covers this paper, and is available at https://soundcloud.com/diane-hope/fewsion-ep-7-mix
Use this link for temporary public access to the new Nature paper: https://rdcu.be/cnVxy