How Do We Estimate Risk and Impact?

There are many techniques for estimating or modelling risk with the simplest based on the statistics of past events and their impacts. For example, risk from flooding is usually determined by an assumption that future floods will follow a pattern similar to events experienced in the past. This means that given enough data from past events, the risk can be determined. However, many natural hazards have little or no historical precedents upon which to properly assess the risk, particularly for rare or extreme events which may have a large impact on society.

To estimate the probability and impact of future events it is necessary to integrate information about past events with physics of earth processes social models of communities, and the economic models of regional and domestic scale. In circumstances in which events are infrequent, thousands of scenarios are developed through simulations to model the probability of an event. Sophisticated computing techniques are also used to capture the interaction of hazard phenomena with the elements at risk and the associated vulnerabilities of the relative elements.

Natural hazard risk models provide the essential building blocks, or tools for coordinating risk assessments as part on an overall risk management framework. At the foundation of this framework is the Australia New Zealand Risk Management Standard (AS/NZ 4360) External site link.

We can estimate, for example, the number of people and buildings affected by the tsunami through combining the results of the hazard modelling (which tells us which areas of the community get wet, how deep the water is and how fast it moves) together with the vulnerability models (which tell us how buildings and people will respond to the water) with the exposure database (which tells us where buildings are as well as their characteristics).

We can then produce maps showing the maximum inundation depth (i.e. the maximum water level reached on the land) and the maximum flow speeds across the community of interest, throughout the duration of a given tsunami. Inundation maps can be used as a planning tool by emergency managers to understand, for example, what infrastructure and services would be potentially damaged during a given tsunami; what roads can be used for evacuation etc. Maps of maximum flow speed can also be used to assist the marine community in preparing for tsunami events.

The development of nationally consistent approaches to risk analysis will allow the identification of areas which are in need of further risk assessments along with those which previously may have been unrecognised as hazardous. This type of information can greatly assist in developing informed and effective policy, funding and mitigation decisions.

Topic contact: hazards@ga.gov.au Last updated: July 15, 2013