National Residential Wind Risk Assessment: A preliminary investigation of Australia's built domain wind risk

A national residential wind risk assessment, the NRWRA, has been undertaken by Geoscience Australia (GA) at the request of the Australian Climate Service (ACS). The NRWRA is one component that will contribute to the overall National Climate Risk Assessment (NCRA), which gives a snapshot of our current understanding of climate related risk in Australia. The NRWRA is a national scale assessment which can be used for high level comparisons of risk across the country and for prioritisation of locations where more regional or local scale assessments should be undertaken to better understand the risk. National scale assessments necessitate simplifications and generalisations in the input data and the modelling process. Consequently, the results outlined in this report may not be appropriate to inform local scale disaster risk reduction policies or activities.

The NRWRA was developed by using hazard, exposure, and vulnerability data and models to calculate impacts. This is known as the HEVI framework. Impacts and risk are a function of all three input datasets and models. The calculation of risk requires that the hazard be known probabilistically, the intensity of the hazard and the likelihood of that intensity occurring, for each location. However, there is currently no probabilistic severe wind hazard model at the national scale for Australia. Due to time constraints, a quasi-probabilistic hazard model was developed using the wind speeds and annual exceedance probabilities defined within the current structural design actions standard for wind (AS/NZS 1170.2:2021). This is a simplification of the severe wind hazard in Australia; however, it is adequate to identify areas of higher and lower risk at the national scale. 

Exposed residential separate and semi-detached houses were used as the exposed elements, since these buildings constitute the majority of the building stock in Australia. GA also has previously developed vulnerability functions for these building types. The exposure data, accessed from the National Exposure Information System (NEXIS) at GA, is generalised to common building types found in Australia. Finally, the vulnerability functions developed by GA, which describe the performance of a building in terms of structural losses for the range of wind speeds it may be subjected to, were used in the assessment.

The results are presented as an average annual loss ratio (AALR) and a decile ranking of Statistical Area Level 1 (SA1) regions across Australia. The AALR allows for a relative risk comparison at the national scale due to severe wind in these regions. The decile ranking provides an easy method of determining where there are concentrations of SA1 regions with above average risk due to severe wind. The results show that, in general, urban areas have lower risk than rural areas, which is likely due to the wind shielding effects of the built environment. The risk varies across the country and there is overall higher risk in coastal areas than in the nation’s interior. Both higher wind hazard in coastal regions and more dense populations in these regions subsequently means more buildings are exposed to the wind hazard.

This assessment provides a good starting point for understanding and quantifying the risk posed to residential buildings in Australia by severe wind. There are several recommendations to improve the assessment and therefore improve the disaster risk reduction policies and actions that can be taken to reduce risk to severe wind in Australia. The key recommendations are:

1.  Undertake a fully probabilistic wind hazard assessment to replace the simplified approach that has been used in the NRWRA.  
2.  Future assessments should incorporate more building types, regionalised vulnerability functions and future climate scenarios to obtain a more comprehensive understanding of the risk posed by severe wind hazard in Australia.

Tags: ACS, Adverse weather events, Australian Climate Service, NCRA, NRWRA, National Climate Risk Assessment, National Residential Wind Risk Assessment, Strategic, Wind, impact, metropolitan and regional planning, risk, severe wind
Organization: Geoscience Australia Data