Victorian 2009 Bushfires Research Response Final Report October 2009

A collaborative trap integrity study between CSIRO and Geoscience Australia evaluated the potential of fault reactivation as a critical exploration risk for hydrocarbon preservation in the Abrolhos Sub-basin. The study is part of a reassessment of the petroleum prospectivity of the offshore northern Perth Basin initiated under the Australian Government's Offshore Energy Security Program. Information on this assessment and a related hydrocarbon seepage survey can be found in AusGeoNews Sep11, issue 103 and AusGeoNews In Brief Dec 11. This study focused on several drilled prospects which are covered by 3D seismic data and contain both breached and preserved oil columns all sourced and sealed by the Triassic Kockatea Shale (Figure 1). Three-dimensional (3D) coupled deformation and fluid-flow numerical modelling has been used to simulate the response of trap-bounding faults to Jurassic-Early Cretaceous NW-SE extensional reactivation in these prospects and, therefore, to investigate hydrocarbon preservation risk in the Abrolhos Sub-basin during this time. The regional trap integrity analysis results are documented in a CSIRO report (link).

The Rapid Inventroy Collection System (RICS) is a vehicular data collection system (image and GPS) used for building/infrastructure damage and inventory assesment. The system consists of Ethernet Cameras attached to a tripod mounted on the roof of a motor vehicle, a GPS device, and software written in C++ and developed using the Agile software development methodology. RICS has been extensively field tested and is ready for deployment at short notice.

We describe a weighted-average approach for incorporating various types of data (observed peak ground motions and intensities, and estimates from ground motion prediction equations) into the ShakeMap ground motion and intensity mapping framework. This approach represents a fundamental revision of ShakeMap technique, particularly as it pertains to processing ground motion and intensity data. Combining ground motion and intensity data onto composite ShakeMaps proves invaluable for loss calibration of historical events as well as for loss estimation in near-real time applications. In addition, the increased availability of near-real-time macroseismic intensity data, the development of new relationships between intensity and peak ground motions, and new relationships to directly predict intensity from earthquake source information, have facilitated the inclusion of intensity measurements directly into the ShakeMap computations. Our approach allows for the possible combination of all of the following data sources and estimates: 1) nearby observations (ground motion measurements and reported intensities), 2) converted observations from intensity to ground motion (or vice-versa), and 3) estimated peak ground motions from prediction equations (or numerical estimates).

We have applied new modelling and analysis techniques to develop a revised understanding of the regional wind hazard across the Tasmanian region. This modelling builds on downscaled global climate simulations from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) over the Tasmanian region, undertaken by the Climate Futures for Tasmania project. These downscaled simulations enabled the development of wind hazard maps for the Tasmanian region both for current climate and also for two climate change scenarios. The wind hazard assessments (current and future climates) were used in a wind risk model to investigate the impact of severe wind risk on residential buildings. Australian Bureau of Statistics population projections were used to scale-up the number of residential structures based on the current ratio of residents per structure. The assessment of wind risk driven by the small increase in the hazard during the 21st century resulted in little or no change to the wind risk associated with the current residential building stock. When population projections were utilised to infer increased number of buildings (all built to the present building code), the proportion of legacy buildings within the building population declined resulting in a decline in wind risk. Wind risk levels remain well below those experienced in the northern part of the Australian continent were high wind hazard, chiefly associated with tropical cyclones, results in risk much greater than that experienced in Tasmania.

Abstract: Understanding how regional climate, and the extremes associated with it, will change over the coming decades is a vital step towards effective local adaptation. The understanding of the vulnerability and risk from severe winds is derived from a number of factors, including the frequency and intensity of the hazard, community exposure and the relationship between gust wind speed and impact/loss associated with residential structures. The Australian Government, through the Australian Building Codes Board (ABCB), has responsibility for maintenance of the Building Code of Australia (BCA), which establishes performance requirements that buildings must satisfy when subjected to the actions of, among other hazards, severe winds. The Australian /New Zealand Wind Loadings Standard (AS/NZS 1170.2, 2002) specifies the gust wind speeds used in calculating loads on structures in different regions of the country. Design wind speeds are similar to wind hazard (both described in terms of return period gust wind speeds), and the levels are set in an effort to equalise the risk between the low and high hazard regions across the country. Areas around the northern coastline are subject to the impact of tropical cyclones, and as such are deemed to experience the highest wind hazard. This results in Australia being divided into four regions, within which the wind speed is broadly similar. Regions C and D are those where the hazard is dominated by tropical cyclones.

Climate change is expected to increase severe wind hazard in many regions of the Australian continent with consequences for exposed infrastructure and human populations. The objective of this study is to provide a nationally consistent assessment of wind risk under current climate and to provide preliminary indications of the effects (impact) of future hazard under several climate change scenarios. This is being undertaken by considering wind hazard, infrastructure exposure and wind vulnerability of infrastructure (residential buildings). The National Wind Risk Assessment (NWRA) will identify communities subject to high wind risk under present climate, and which will be most susceptible to any climate change related exacerbation of local wind hazard. While there is significant uncertainty on what the likelihood of extreme winds will be in the future, the understanding of current local wind hazard for the Australian region is also in need of improvement. Australian wind hazard is based on the statistical analysis of extreme wind observations and engineering judgement. Observations include peak 3-second gusts captured at about 30 meteorological measurement stations, mainly located at significant city and regional airports. These provide poor spatial texture with regard to wind hazard. This study is taking advantage of modelled wind hazard assessments (current climate) being developed at Geoscience Australia utilising separate techniques for the three main wind hazards: tropical cyclones; thunderstorms; and synoptic winds. A stochastic model based on observed and modelled cyclone tracks is used to obtain an understanding of cyclonic wind hazard, whilst two statistical approaches involving observed and modelled vertical instability and mean wind speed fields (via high-resolution regional climate model) are the basis for the thunderstorm and synoptic wind hazard.

Climate change is expected to increase severe wind hazard in many regions of the Australian continent with consequences for exposed infrastructure and human populations. The objective of this study is to provide a nationally consistent assessment of wind risk under current climate and to provide preliminary indications of the effects (impact) of future hazard under several climate change scenarios. This is being undertaken by considering wind hazard, infrastructure exposure and wind vulnerability of infrastructure (residential buildings). The National Wind Risk Assessment (NWRA) will identify communities subject to high wind risk under present climate, and which will be most susceptible to any climate change related exacerbation of local wind hazard. While there is significant uncertainty on what the likelihood of extreme winds will be in the future, the understanding of current local wind hazard for the Australian region is also in need of improvement. Australian wind hazard is based on the statistical analysis of extreme wind observations and engineering judgement. Observations include peak 3-second gusts captured at about 30 meteorological measurement stations, mainly located at significant city and regional airports. These provide poor spatial representation with regard to wind hazard. This study is taking advantage of modelled wind hazard assessments (current climate) being developed at Geoscience Australia utilising separate techniques for the three main wind hazards: tropical cyclones; thunderstorms; and synoptic winds. A stochastic model based on observed and modelled cyclone tracks is used to obtain an understanding of cyclonic wind hazard. Two statistical approaches involving observed and modelled vertical instability and mean wind speed fields (via high-resolution regional climate model) are the basis for the thunderstorm and synoptic wind hazard.

Severe wind damage accounts for about 40 percent of the total building damage observed in Australia during the 20th century. Climate change has the potential to significantly affect severe wind hazard and the resulting level of loss. W report on a nationally consistent assessment of severe wind hazard across the Australian continent, and also severe wind risk to residential houses (quantified in terms of annualised loss). A computational framework has been developed to quantify both the wind hazard and risk due to severe winds, based on innovative modeling techniques and application of the National Exposure Information System (NEXIS). A combination of tropical cyclone, synoptic and thunderstorm wind hazard estimates is used to provide a revised estimate of the severe wind hazard across Australia. The hazard modeling utilises both 'current climate' information and also simulations forced by IPCC SRES climate change scenarios (employed to estimate how the wind hazard may be influenced by climate change). Our analysis has identified regions where the design wind speed depicted in the Australian/New Zealand Wind Loading Standard (AS/NZS 1170.2, 2010) is lower than 'new' hazard analysis. In considering future climate scenarios, four case study regions are used to illustrate when the wind loading standard may be inadequate, and where retrofitting is indicated as a viable adaptation option at either the present or at a specified future time. The comparison of current and projected future risk, currently only considers direct costs (structural damage to houses) associated with severe wind hazard. A broader assessment methodology is discussed.

The National Wind Risk Assessment (NWRA) has developed a computational framework to evaluate both the wind hazard and risk due to severe wind gusts. A combination of tropical cyclone, synoptic and thunderstorm wind hazard estimates is used to provide a revised estimate of severe wind hazard across Australia. A national assessment of localised wind speed modifiers including topography, terrain and the built environment (shielding), has also been undertaken to inform the local wind speed hazard that causes damage to structures. Wind speed modifiers are incorporated through a statistical modification of the regional wind speed. The regional hazard modelling utilises both current-climate information and also simulations forced by IPCC SRES climate change scenarios, which are employed to determine how wind hazard will be influenced by climate change. We report on a national assessment of severe wind impact and risk to residential housing (quantified in terms of annualised loss). Results from the current climate regional wind hazard assessment are compared with the hazard based on the existing understanding as specified in the Australian/New Zealand Wind Loading Standard (AS/NZS 1170.2, 2011). Regions where the design wind speed depicted in AS/NZS 1170.2 is significantly lower than the hazard analysis provided by this study were mapped. These regions are discussed in the context of the minimum design standards in the building code regulations, where the development of adaptation options is likely.