Interdependence

Complex, interconnected, and interdependent have become definitive terms reflecting the reality of the dependence of modern lifestyles on the infrastructure that sustain them. The global economy is increasingly dependent on interconnected networks of infrastructures that are spread across multiple temporal and spatial scales and serve as the critical lifelines to the functioning of modern society. Interdependence in the simplest definition is understood as a condition of mutual dependency. The concept of interdependence can be applied to an organization, a community, infrastructure, nation-states, or the global financial system. Interdependent organizations, infrastructures, or nation-states are those where the function of one entity is dependent on and influenced by the other entity. This interdependence provides new avenues of increasing vulnerability, where increases in the complexity and tight coupling of critical infrastructures and economic and social systems allow relatively small disturbances to rapidly escalate into compound crises. This article focuses on infrastructure interdependence given the critical importance of functioning for crisis management.

Just-in-time supply chains, reliance on electronic systems, planning and development patterns that promote the physical collocation of infrastructure/utility corridors, aging infrastructure and increasing congestion, the increasing intensity and incidence of severe weather events, and potential cyber/terrorism attacks are among many factors cited for increasing interdependencies. Disruptions in one infrastructure can cascade, affecting dependent infrastructure sectors. Failures in these sectors feed back into the initially impacted sector, transcending through the public and private companies, impacting essential services with far-reaching health and human safety, societal, economic, environmental, and national security consequences.

For example, the dependence of water and wastewater infrastructure on electricity for pumping and for operation of treatment facilities, control systems, and monitoring systems is obvious to most users of these systems. Water and wastewater systems are also dependent on repair and maintenance personnel, who are reliant on transportation, which is reliant on a continuous supply of fuel. The sector is also reliant on communications for ordering supplies and equipment and on financial systems to support billing, payments, and other business services. Similarly, the electricity industry depends on fuel supply, road and rail transportation to deliver fuel to the generators, water for cooling and to reduce emissions, and telecommunications to monitor system status and system control. Acknowledging and addressing these interdependencies is an important task for infrastructure planners and operators as part of risk and crisis management strategies at the planning, response, and recovery stages.

Understanding the nature and the types of interdependencies is the first important step toward this task. Stephen Rinaldi, James Peerenboom, and colleagues, in their seminal work, defined four types of infrastructure interdependencies: physical (e.g., the material output of one infrastructure is used by another), cyber (e.g., infrastructures utilize electronic information and control systems), geographic (located in close spatial proximity), and logical (e.g., infrastructures are linked through financial markets). Infrastructure interdependencies vary significantly in scale and complexity, ranging from local linkages (e.g., municipal water supply systems and local emergency services), to regional linkages (e.g., electric power [British Columbia Hydro]), to national linkages (e.g., interstate transportation systems), to international linkages (e.g., telecommunications and banking and finance systems).

...