Vulnerability has been defined as the degree to which a system, or part of it, may react adversely during the occurrence of a hazardous event. This concept of vulnerability implies a measure of risk associated with the physical, social and economic aspects and implications resulting from the system’s ability to cope with the resulting event. Concepts of resilience take two broad forms, namely:
- Hard resilience: the direct strength of structures or institutions when placed under pressure. In the disaster context, resilience is often treated as the simple inverse of fragility. Engineers, for example, often refer to increasing the resilience of a structure through specific strengthening measures to reduce their probability of collapse with respect, for example, to earthquake intensities, wind loading or other physical stresses. As resilience increases, the degree of damage for a given intensity hazard decreases.
- Soft resilience : the ability of systems to absorb and recover from the impact of disruptive events without fundamental changes in function or structure.