Address-based natural hazard risk ratings focus on the peril – earthquake, flood, hail, bushfire, etc. – rather than the probability or severity of any resulting property damage. In interpreting these risk ratings, it should be noted that building damage is often non-linearly related to peril magnitude or intensity and also dependent upon structural considerations including building age in some cases.

All perils are ranked on 5-point scales with 5(1) referring the most (least) severe.

Bushfire and flood ratings refer to individual street addresses while hail storms, earthquakes and tropical cyclones refer to larger scales - Census Collection Districts, Postcodes or coastal zones - that include the specified address. Address location refers to the centroid of the land parcel and the actual location of the asset within the property should be noted particularly in respect of flood and bushfire. Risk ratings cover both residential and commercial addresses. Elevation refers to the height above mean sea level, and its accuracy depends on the resolution of the best available Digital Terrain Model; this will vary between sites, ranging from 5m to 90m.

This document is not a substitute for a site inspection. Rather it should be treated as a means to raising awareness of possible natural perils and enabling better value to be obtained from such an inspection.

Hazard Scales

Bushfire

Analysis by Risk Frontiers of major historical bushfires show distance from the bushland fringe to be the single-most important factor determining the probability of building destruction given an extreme fire ¹ in adjacent bushlands. A five-point scale is applied to addresses in bushfire-prone areas:

Areas with a high potential for bushfire are largely confined to the southeast and southwest of the continent and Tasmania ². Areas north of the Tropic of Capricorn do experience bush or grassfires but to date have not involved significant property losses. Accordingly we do not categorise bushfire risk in these areas.

Site elevation and aspect are provided in the Address Information section.

Note that the existence of corridors of trees between extensive areas of bushland may aggravate risk beyond the risk rating provided despite the distance between the building and the bush. On the other hand, specific site factors or owner preparedness may mitigate this risk.

Mainstream Riverine Flood

The probability of experiencing a flood of a particular magnitude is generally expressed as an average recurrence interval (ARI) in years. The ARI is the average interval between events affecting the property. It is an average taken over a very long period so a 20-year ARI flood does not occur regularly every 20 years. A flood in a particular catchment with an ARI of 100 years is often used to define a severe flood for planning purposes.

Two flood risk measures are provided: (1) the ARI (in years) of inundation of the address at ground level, and (2) the water depth during a flood with an ARI of 100 years. The first metric represents the probability of flooding at the property and it is this that dictates the Overall Risk. The second provides a surrogate indication of the potential loss from flooding as water depth is a key determinate of damage. Both measures refer to the centroid of the land parcel. The actual location of buildings with respect to the centroid may increase or decrease risk to property.

ARI is categorised into 5 levels and the Overall Risk (right hand column) is based on this table:

The Probable Maximum Flood is the most severe flood considered possible by hydrologists and has an ARI in excess of 10,000 years.

The ratings are for riverine flooding only and do not indicate the risk of flash flooding or storm water overflow. The risk ratings incorporate the effect of levees and it is assumed that the levees operate as designed.

Ratings are available for 1.3 million of the most flood prone addresses in Australia .

For information about coastal flooding refer to the Tropical Cyclone section.

Earthquake

Australia is located entirely within a tectonic plate and experiences low to moderate levels of seismic activity compared with say Japan , New Zealand and California . Nonetheless destructive earthquakes have occurred as witnessed by the 1989 Newcastle earthquake (M L = 5.6), which resulted in some $1.1 billion (Year 2003 dollars) in insured losses. Poor building stock, in particular, older unreinforced, masonry construction can exacerbate losses from even modest levels of ground shaking. Newer engineered structures or smaller wood-framed buildings are much less susceptible.

Building codes prescribe how much horizontal force building should be able to withstand during an earthquake. Peak Ground Acceleration (PGA) is an estimate of the maximum horizontal acceleration experienced by a solid mass at the soil surface in an earthquake. The 5–point peril scale adopted here is based on PGA from the Global Seismic Hazard Assessment Program (GSHAP) ³. This scale gives peak ground accelerations in bedrock having a 10% chance of exceedance in 50 years (equivalent to a 475 ARI).

The actual ground shaking intensity felt at ground level can be strongly modulated by the response of the soils and weathered material overlying basal rocks. This tendency to amplify ground motions is given by a five-point ground zonation developed by Blong ⁴. The simplified version is as follows:

The Overall Rating (right-hand column) is the based on the product of the PGA value on bedrock and Ground Zonation amplification factors that vary between 0.6 and 2.0 between Zones 1 and 5.

Hail

Hailstorms can cause substantial damage to property. The April 1999 hailstorm in Sydney caused $1.7 billion (2003 dollars) in insured losses, making it Australia "s most costly natural disaster. Most areas on the mainland south of the Tropic of Capricorn are at risk from hail. Damaging hail is rare in the tropics and in Tasmania . Hail risk is a function of the intensity and frequency of hail, where intensity is represented by hail stone size and frequency is the number of storms per unit area per year ⁵.

The 5-tier risk scale is based on the product of maximum-recorded hail stone size and the normalized annual frequency for key locations around the country.

Tropical Cyclone

Tropical cyclone wind risk in Australia is analysed on a broad scale with risk varying both along the coastline and with the distance inland for regions north of latitude 30°S. A five-tier scale is used to categorise the risk geographically, based on Risk Frontiers" frequency-magnitude analysis of past cyclones and allowing for the decay of cyclone wind intensity with distance inland. An annual probability of occurrence at a 1% level (ARI of 100 years) is applied to categorise risk levels for tropical cyclone prone coastal areas.

The ratio of damage between scales is roughly proportional to damage ratios used in the widely-used 5-point Saffir-Simpson Hurricane Scale.

Proximity to shorelines refers to the shortest distance between an address and shorelines of any coastal waters (e.g., rivers, lakes, lagoons and estuaries) that are directly connecting to open ocean. The accuracy of this calculation is about 1km.

An indication of storm surge risk can be attained by considering the elevation in the Address Information and the distance from the shoreline provided.

Coverage

The coverage of the underlying database is national although Risk Frontiers does not claim that all attributes are currently available for all addresses.

While Access Macquarie Limited, through Risk Frontiers - the Natural Hazards Research Centre, has gathered an extensive database of addresses in Australia , we cannot guarantee that a Risk Profile report can be provided for each address. This could be due to the fact that the address is not contained in our database or the address details provided by the client do not match any contained in our database due to misspellings or incorrect data entry.

Disclaimer

The purpose of this report is to provide an overview of the natural hazards affecting an individual address or geographical area in which the property is located. It is not a substitute for an on-site inspection or review of other available reports and records. It is not intended to be, and should not be taken to be, a rating or assessment of the desirability or market value of the property or its features. In the preparation of this report, Risk Frontiers has relied on data provided by third parties and while all reasonable care has been used to review the data for reasonableness it is not possible within the context and scope of this report to verify the accuracy and completeness of that data.

Access Macquarie Limited, Macquarie University and MapData Sciences their officers, employees, agents or contractors and the authors are not liable for any loss (including legal costs and expenses), injury or damage including death, economic loss and consequential loss or liability incurred or suffered by any recipient of this report or their successors in title or any other party acting or purporting to act in reliance on the contents of this report.

¹Chen, K and McAneney, K.J. 2004. Quantifying bushfire penetration into urban areas in Australia . Geophysical Research Letters. 31, L12212, doi:10.1029/2004GL020244.

²Blong, R, Sinai, D, and C. Packham. 2000. Natural Perils in Australia and New Zealand . Swiss Re Australia Ltd.

³The Global Seismic Hazard Assessment Program (GSHAP), 1999. http://www.seismo.ethz.ch/GSHAP/

⁴ Greig Fester. 1997. Earthquake PML: Household Buildings Sydney II. Greig Fester ( Australia ) Pty Ltd.

⁵Leigh, R. and Kuhnel, I. 2001. Hailstorm loss modeling and risk assessment in the Sydney region, Australia . Natural Hazards, 24:171-185.