Resilience of Hierarchical Network-of-Lifeline-Networks Under Compound Weather Extremes

Weather extremes are not just intensifying under climate change but also growing more widespread and correlated across space and time. Compound weather extremes—defined as the simultaneous occurrence of such events, or where successive extremes occur before the impacted systems get a chance to recover—are becoming real threats. Meanwhile, built systems such as communication-transportation-water-energy networks, natural systems such as ecological networks and food webs, and human systems such as financial services and social networks, are not just growing more interconnected/interdependent within urban or national boundaries but also beginning to defy geographical or jurisdictional boundaries. The interconnectedness is from factors, such as increasing human mobility and transport, globalization of economies, policy ramifications, and interdependence of infrastructures. The consequences have been stunning: a relatively small failure at urban scales may cause catastrophic collapses and cascading failures of the entire system at national or international levels. We can see this through local power outages impacting international airspace networks or shocks in regional economic markets impacting the entire globe. The growing interdependence of natural-built-human systems at urban, regional, or national scales have led to network-of-networks representations and studies on the resilience of such systems. However, what also needs to be considered is the dependence of these networks-of-networks across scales ranging from urban communities to entire cities and onto megalopolises, nations, continents, and the entire globe. Thus, a hurricane-induced cascading failure of critical lifelines including transportation, communication, and power in New York City may disrupt city airports which would then cascade to national and global scale failure of airspace networks, while urban power grid failures resulting from excessive demand for air conditioners during heatwaves may percolate to emerging urban corridors and then to more significant regions, with power and transportation failures further impacting each other. Here we motivate a framework that can examine such interconnected and interdependent hierarchical network-of-networks subjected to compound weather extremes. The extent to which our current scientific understanding, state-of-the-art technologies, financial instruments, and policy or governance principles, can address these challenges is described, and new developments are motivated to address fundamental gaps.