Infrastructure Interdependencies - - Types of Interdependencies

We typically come across interdependencies in one of four principal classes (Keep in mind interdependencies are not mutually exclusive):

1. Physical Interdependency - - The first type of interdependency arises from a physical linkage between input and outputs.  The rail networking and the coal-fired power plant are physically interdependent - - given that each supplies commodities that the other requires to function properly.  The state of one directly influences the state of the other.  Perturbations in one can ripple over to the other.
2. Cyber Interdependency - - This is relatively new - - yet growing exponentially.  To a large degree, the reliable operation of modern infrastructures depends on computerized control systems - - from SCADA systems that control electric power grids to computerized systems that manage the flow of rail cars and goods.in the rail industry.  This has produced the modern axiom - - "The states  of infrastructures depend on outputs of the information infrastructure."
3. Geographic Interdependency - - Infrastructure are geographically interdependent if a local environment event can create state changes in all of them.  An electrical line and a fiber-optic communications cable slung under a bridge connect (geographically) elements of the electric power, telecommunications, and transportation infrastructures.  The interdependency in this case is simply due to proximity - - the state of one infrastructure does not influence the state of another.  Traffic across the bridge does not influence the state of another.  Traffic across the bridge does not influence the transmission of messages through the optical fiber or the flow of electricity.
4. Logical Interdependency - - Two infrastructures are logically interdependent if the state of each depends on the state of the other via a mechanism that is not a physical, cyber, geographic connection.  Logic interdependencies may be more closely likened to a control schema that links in one infrastructure without any direct physical , cyber, or geographic connection.  The linkage between a municipal water treatment and distribution system and the financial infrastructure is a good example.

Munich Re is the world's biggest re-insurer.  In the December 6, 2010 issue of Bloomberg Businessweek, their chief risk officer, Joachim Oechslin sums all the concerns regarding interdependencies with the following:

"The most significant changes in risk management have taken place in the past 7 to 10 years.  Today it's not only about data gathering  - - but trying to figure out the relationship of things."