## 2 Critical Infrastructures (CIs)
### Interdependence Types
In this case, the relationship between the infrastructures is established through a logical connection, rather than a direct physical, cyber, or geographic link. * **Cyber Interdependence:** Cyber interdependence manifests between infrastructures when they are directly linked via an information exchange within an informational infrastructure. This form of interdependency connects critical infrastructures through informational pathways, where one infrastructure's output data serves as another's input. Such an exchange between infrastructure systems must inherently involve data transfer. Consider, for example, the typical operation of communication systems, which depends on the electrical power generated by power plants and distributed via transmission systems. To guide this electricity to the required systems, a Supervisory Control and Data Acquisition (SCADA) system is utilized to administer the electric power networks. The SCADA system leverages communication systems to send and collect information from diverse power sectors, thus establishing a cyber interdependency nexus between the power and communication systems. * **Geographic Interdependence:** Geographic interdependence occurs when multiple infrastructure systems are situated within the same local area, which can result in functional changes to all systems involved in the event of a disruption [24]. For example, during the 9/11 attack on the World Trade Center, the collapse of the buildings caused functional disruptions to water systems, rail tunnels, a passenger station, and one of the world's largest telecommunication nodes [22]. * **Social Interdependence:** Social interdependence arises when the connection between two smart interdependent infrastructures is partially rooted in human behavior outcomes. Healthcare and other critical infrastructures are not standalone operations; rather, they are embedded in a vast network of interdependent structures. Their operation and effectiveness are heavily reliant on the proper functioning of other critical infrastructures, demonstrating their intricate interdependence. For instance, healthcare systems depend on the reliable supply of electricity for life-supporting equipment, telecommunication networks for data transmission and coordination, transportation systems for the mobility of patients and staff, and water systems for sanitation and hygiene. When a disruption occurs in any of these supporting infrastructures, it can have a profound impact on the healthcare system. For example, a power outage can incapacitate essential medical equipment, compromising patient care and even leading to loss of life in extreme cases. Similarly, a failure in the transportation system might prevent patients from reaching hospitals or delay the delivery of critical medical supplies. This is where the social interdependence between these systems becomes apparent. The community relies on these interdependent infrastructures for their health and well-being. Disruptions can not only affect physical health but also cause stress and anxiety, impacting the community's overall social and mental well-being. Thus, the resilience of one infrastructure directly influences the resilience of others and in turn, the resilience of the society they serve. It underscores the need for a holistic, system-of-systems approach to resilience planning, ensuring that each infrastructure can withstand, adapt to, and recover from disruptions, thereby safeguarding the community's health and wellbeing.