The Importance of Prehistoric Data and Variability of Hazard Regimes in Natural Hazard Risk Assessment – Examples from Australia

Natural hazards are normally viewed as events that occur randomly overtime. This precept usually forms the basis for the development of the hazardmagnitude-recurrence interval relationship used in risk assessments. However,hazard variability does not always conform to this relationship especially overlonger time intervals. Non-stationarity can be common with some hazards andthose periods where the variability and/or mean (magnitude/frequency) remainconstant are referred to here as hazard regimes. Shifts from one regime to anotheroccur at a variety of time scales from centuries to millennia. Regime shifts areoften only discernible by examining longer-term records which usually includeprehistoric data. Risk assessments frequently ignore these regime shifts andestimates of the risks associated with tropical cyclones, tsunami, terrestrialfloods and landslides in Australia have been both under-estimated and exaggeratedwhen such assessments have been based solely upon short historical records.Examples of these regime shifts and their significance for natural hazard riskassessment are presented here. Copyright Kluwer Academic Publishers 2003