How Do We Model Exposure?

We model exposure by building and compiling a comprehensive dataset that is categorised into different sectors based on building use and occupants. This dataset is referred to as NEXIS - the National Exposure Information System. The spatial location of exposed elements is highly critical for assessing the risk and modelling impact for all hazards.

We collect and synthesise data from a range of sources to identify the location of buildings, the number of occupants and the use of the building, such as whether it’s residential, commercial, industrial or institutional. We also incorporate a number of statistical assumptions to calculate the building type (house or apartment), age, structure (wall and roof type, number of storeys), household income/business turnover, building construction and replacement costs.

Modelling features specific to separate classes of buildings are described below. Each of these building classes is significant for the assessment of socio-economic impacts on communities and emergency management.

Residential exposure

The variables required to assess the risk for the residential areas are primarily spatial, structural (age, wall and roof type, building area, construction and replacement value) and demographic (number of residents, income level and contents value).

In the absence of comprehensive residential exposure information, some generic assumptions are made to derive the information required for risk assessments.

For example, a large amount of Geocoded National Address File (GNAFs) located in a cadastral parcel identifies the building as a residential apartment block. Australian Bureau of Statistics (ABS) Census provides statistics of building wall and roof type which is applied based on the buildings location (City or Rural) and building type (house or apartment). ABS also provides demographic statistics (household income and population) which are randomly distributed within a Census district. Cost factors are then applied calculating construction and replacement values.

Commercial and industrial exposure

Risk assessment for the business sector from natural disasters is much more complex than in the residential sector. This component of exposure information captures the usage of buildings and business operations using Australian and New Zealand Standard Industrial Codes (ANZSIC) classification categories, number of storeys, building structure, building footprint, employment, customer capacity and business turnover.

Geoscience Australia undertakes surveys to collect building structure information as part of the post disaster survey programme. This information is fed back into NEXIS to improve the building level data for that area. It builds our knowledge of business construction materials and their vulnerability to damage. Using real vulnerability information in prescribed scenarios allows us to identify particular areas under threat and assess the damage for potential hazards. This allows emergency managers to develop plans and strategies to mitigate and respond to future scenarios based utilising an evidence base. 

The Cityscope database provides details on every property within the Central Business Districts (CBD) of most major cities in Australia. It provides consistent information about the businesses, tenants, owners and size but lacks information about building structure. In the process of making nationally consistent exposure information for Commercial buildings, a generic approach has been utilised where real data is not available. This generic approach fills the gaps using assumptions based on the actual data from the Geoscience Australia Survey and Cityscope databases.

Institutions exposure

Institutions include educational, health and sports facilities, government buildings and emergency services.  The population information associated with the institutions is highly difficult to derive as it is not being collected as a part of any census. It will also vary with time and events.  The population dynamics through time is planned to be captured by activity model development.

Infrastructure exposure

Infrastructure includes transport (road, rail, stations, bridges, tunnels, ports and airports), communications (antennas, exchanges and towers), energy (fuel and power assets) and water. Information of these assets available in the public domain is collected and maintained in NEXIS.

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