Vulnerability of Australian Houses to Riverine Inundation : Analytical and empirical vulnerability curves

Vulnerability functions, that relate damage to hazard magnitude are used in risk and impact assessments, mitigation studies and associated cost benefit analyses. The development of vulnerability functions must address the variety of assets exposed to the hazard of interest and the common scarcity of empirical data to calibrate any functions developed using heuristic or analytical methods. This record reports efforts to improve the knowledge of the vulnerability of Australian domestic housing to riverine inundation. The research is focussed on housing types found in the south-east of Queensland although the results can be applied to houses of similar type elsewhere in Australia. In order to address the wide variety of housing types found in the Australian built environment, in this research representative generic housing types are identified from surveyed building exposure. Analytical vulnerability relationships are developed for each from assessments of repair works at different inundation depths. Finally, the analytical vulnerability curves are compared to empirical data derived from repair costs reported by postal surveys of dwellings affected by flooding in Brisbane-Ipswich, January 2011, and Bundaberg, January 2013. Analytical vulnerability curves are presented for twelve generic housing types and two insurance regimes. The process of developing vulnerability curves analytically is compared to empirical data. The empirical data shows that for insured houses, the analytically derived vulnerability curves provide a reasonable estimate of direct losses. However, for uninsured houses the analytical vulnerability curves are shown to overestimate direct losses. The difference may be due to uninsured residents tolerating a greater level of residual damage or undertaking repairs themselves at cheaper rates than those assumed for the analytical work. Although the results display variability, the empirical data indicate that the presented analytical methodology for constructing vulnerability curves yields reasonable curves that would be suitable for modelling impact of riverine flooding on populations of houses provided that adjustments are made to modelled losses for uninsured dwellings.