What is Risk?
The concept of risk combines an understanding of the likelihood of a hazardous event occurring with an assessment of its impact, for example:
Risk = Hazard x Elements at Risk x Vulnerability
Hazardous events can be either naturally occurring, such as earthquakes, tropical cyclones or coastal erosion, or they can be human-made, such as water pollution or terrorist attack. In addition, events can be sudden as in the case of an earthquake, or they can occur over time as in the case for most environmental hazards.
The impact of a hazardous event depends on the elements at risk, such as; population or buildings and their associated vulnerability to damage or change as a result of the event. Estimating risk is an uncertain science because it involves forecasting events for which the time and the location may be largely unknown. This uncertainty is captured mathematically in terms of probability.
The total risk may be decreased by reducing the size of any one or more of the three contributing variables, the hazard, the elements exposed and/or their vulnerability. This can be illustrated by assuming the dimension of each of the three variables represents the side of a triangle, with risk represented by the area of the triangle.
In the risk triangle below, the larger, yellow area portrays each of the variables as being equal while in the smaller, green space the total risk has been mitigated by halving both exposure and vulnerability. The reduction of any one of the three factors to zero consequently would eliminate the risk.