How Do We Model Hazard?

Model of tsunami scenario

Model of tsunami scenario
© Geoscience Australia

A physical based model estimates the underlying processes of the hazard event. Although each hazard manifests differently and requires different model parameters, the basic framework is the same. As a result, the problem can be divided into two parts:
  • the probability of the event or hazard scenario occurring
  • the propagation of the event through the atmosphere (e.g. windstorm), the Earth's sub-surface (e.g. earthquake), on the surface (e.g. flood), or a combination. For example, modelling storm surge is a combination of atmosphere and surface aspects, and tsunami is a combination of sub-surface and surface models.

In the case of an earthquake, the rate at which earthquakes of various magnitudes happen at any location defines the probability of occurrence while a specific event is expressed through the pattern of ground shaking resulting from seismic waves travelling though the Earth. For floods, the event is governed largely by rainfall and the geological and hydrological characteristics of the water catchment influence the water flow and the extent of the flood.

Techniques for modelling various hazards are generally well developed. However, hazard models are only as good as the data used to define them. Historical catalogues for earthquakes, floods, fires, landslides, tsunamis, volcanoes, severe storms and tropical cyclones are critically important. Because the historical record in Australia extends only about 150 to 200 years, analysis often requires extrapolating the effects of historical events to potentially catastrophic or probable maximum events. If the underlying hazard process is understood, then the model parameters can be defined that allows extrapolation in a realistic and scientifically credible manner. In addition, the information from hazards that have occurred in a specific location can be used by applying appropriate modifications to estimate the effects when applied to another scenario.

The ability to adapt models to local characteristics is highly dependent on the availability of detailed data on geology, vegetation, elevation and other geophysical information such as geodetic measurements as well as basic meteorological information such as rainfall and temperature. To determine future trends in hazardous events, models also need to incorporate potential effects of climate change and urbanisation, which may differ substantially from the past.

Topic contact: hazards@ga.gov.au Last updated: December 10, 2012