large scale natural disaster) is also potential area for future modeling. Next, a deeper analysis of the tradeoffs between efficiency, connectedness, islanding and other grid structures, particularly in the broader context of resilient electricity provision during and after a natural hazard event, may provide useful insights into the planning process.

- 3) A finding across the literature reviewed on the impacts of natural hazards on the power system  is that transmission networks are the most vulnerable component of the system (Schweikert et al. 2018).  Several research areas specific to natural hazards and resiliency can be framed in this context.  The deeper analysis of smaller systems, such as Puerto Rico or other geographically isolated regions, may provide valuable insights into the operation and topological considerations that increase or reduce resiliency.  This could include different measures of intermittent generation technologies, redundant transmission networks, and others.  A final consideration in this context is a multiplecriterion assessment of transmission reliability that includes a techno-economic analysis of performance during a hazard situation, the cost of redundant transmission lines and the consideration of above or below-ground transmission lines.

# **CONCLUSIONS**

A functioning and reliable power system is important for the operation of many societal functions, including lifeline infrastructure systems. In hazard situations, damage to the electrical grid, or supply chains, can result in cascading failures throughout a society and impact response and recovery work. This was seen in the impacts of recent hurricanes in both Puerto Rico and the Northeastern United States (see: Schweikert et al. 2018 and Comes and Van de Walle 2014).

This paper provides a primer on the vulnerabilities of networked energy infrastructure. Notably, much of the work reviewed shows that these types of systems, including the electricity grid, can exhibit non-linear and unpredictable behavior. Metrics including density of networked components, the redundancy and interconnectedness of sub-systems within the electricity grid – as well as linkages to other lifeline networks – are identified as providing insight into system behavior. However, these metrics are not particularly well understood or quantified, especially in smaller systems or those existing in developing economic regions.

Future work in this area, aimed at enhancing decision making and investment for more resilient infrastructure, can focus on the following areas:

- a) Develop data on the connectivity of lifeline infrastructure systems to determine key interdependencies and how these vary geographically or with other parameters such as per capita GDP or HDI;

- b) Use data on ports of entry and transportation infrastructure to identify regions where supply chain bottlenecks could impact lifeline infrastructure;

- c) Use high spatial and temporal resolution global historical data on wind velocities to determine where electricity grids would be particularly susceptible to damage;

- d) Develop a methodology to identify lifeline infrastructure systems that lack important redundancies.

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