Lifeline Interdependency Analysis

Physical, cyber, geographic, and logical. Physical interdependency exists when one infrastructure's output is another's input, such as electricity powering water pumps. Cyber interdependency runs through information and control systems, such as a utility's reliance on telecommunications for SCADA control. Geographic interdependency arises when components share a location, so a single local event — a flood in a shared utility corridor — affects several systems at once. Logical interdependency covers couplings through markets, regulation, or human decisions that are not physical, cyber, or geographic. The taxonomy, from Rinaldi and colleagues, organizes how disruptions propagate between systems.

Because they make a disaster's reach far larger than the directly damaged components. A single failure can cascade: losing power can stop water treatment, telecommunications, fuel distribution, and traffic control, and feedback loops can deepen and prolong the disruption. Analyzing each system alone would miss these chains and badly underestimate the consequences. Interdependency analysis captures the cascade, explaining why outages spread across sectors and why some seemingly minor components are in fact linchpins of the whole system.

Restoration is itself governed by interdependencies: you often cannot restore one system until another it depends on is back. Interdependency analysis identifies these restoration dependencies and the components whose recovery re-enables the most downstream services, allowing planners to sequence repairs efficiently. The resulting time profile of restored functionality feeds directly into recovery-curve and resilience analysis, linking the structure of infrastructure couplings to how quickly community functionality returns after a disaster.