Understanding cascading risks through real-world interdependent urban infrastructure

The prevalence of cascading failures is growing as infrastructure becomes more interdependent and climate change exacerbates more extreme hazards. After such events, the general focus is on the magnitude of direct damage or loss; it is less understood how events trigger failures throughout other infrastructure. In this work, we present a methodology to model direct and indirect impacts from an event for a multi-system network, including interconnected infrastructure and end users. We perform a case study of New Zealand's second largest city, Christchurch, investigating electricity, water supply, and wastewater networks following a range of coastal flooding events and climate change scenarios. For a 10-year average recurrence interval event given no sea-level rise, there is a 216% increase from directly impacted end users to the total number of end users that have lost at least one utility. For the same scenario, this metric is 71%, 129%, and 131% for end users who have lost electricity, water, and wastewater, respectively. The results show a larger estimate of impact on residents and a more geospatially-varied loss of service. This methodology provides insight for utility operators, emergency response, and communities on node criticality, areas of impact, and resource requirements after an event occurs.