Risk, vulnerability, robustness, and resilience from a decision-theoretic perspective

Risk, vulnerability, robustness, and resilience are terms that are being used increasingly frequently in a large range of sciences. This paper shows how these terms can be consistently defined based on a decision-theoretic, verbal, and formal definition. Risk is conceived as an evaluation of an uncertain loss potential. The paper starts from a formal decision-theoretic definition of risk, which distinguishes between the risk situation (i.e. the risk analyst's model of the situation in which someone perceives or assesses risk) and the risk function (i.e. the risk analyst's model about how someone is perceiving and assessing risk). The approach allows scholars to link together different historical approaches to risk, such as the toxicological risk concept and the action-based approach to risk. The paper then elaborates how risk, vulnerability, and resilience are all linked to one another. In general, the vulnerability concept, such as the definition of vulnerability by the Intergovernmental Panel on Climate Change (IPCC), goes beyond risk, as it includes an adaptive capacity. Thus vulnerability is mostly seen as a dynamic concept that refers to a certain period of time. If the vulnerability of a system is viewed only at a certain point of time, vulnerability equals risk. In contrast, if we consider dynamic risk in the sense that we include actions that may follow adverse events, risk resembles vulnerability. In this case we speak about adaptive risk management. Similar to vulnerability, resilience incorporates the capability of a system to cope with the adverse effects that a system has been exposed to. Here we distinguish between specified and general resilience. Specified resilience equals (dynamic) vulnerability as the adverse events linked to threats/hazards to which a system is exposed to are known. Robustness can be seen as an antonym to (static) vulnerability. General resilience includes coping with the unknown. In particular, the approach presented here allows us to precisely relate different types of risk, vulnerability, robustness and resilience, and considers all concepts together as part of adaptive risk management.