Risk Assessment of Climate Adaptation Measures for Australian Housing Subject to Extreme Wind Events

Abstract eng:
Climate change researchers suggest that significant alteration in severe wind intensity and frequency are possible within the lifetime of existing infrastructure in Australia. The current Australian Standard "Wind Loads for Houses" AS4055- 2006 is the reference standard used to determine the appropriate wind classification for design of residential (domestic) housing. These wind classifications are then used to determine appropriate deemed-to-comply sizing and detailing requirements for residential construction. However, the wind classifications may be inadequate if wind speeds increase due to a changing climate. The vulnerability of new residential construction may be reduced by increasing design wind speeds to resist 50% higher wind pressures. The economic viability of such an adaptation option at a regional scale is affected by both spatiality in construction distribution and temporal uncertainty in extreme wind development. The present paper will assess the damage risks, adaptation costs and cost-effectiveness of these adaptation measures for residential construction in Queensland cities to 2100. The stochastic analysis includes the effect of climate change on time-dependent wind field characteristics, costs of adaptation, timing of adaptation, discount rates, future growth in new housing, and fragility of houses to wind speed. The criterion for cost-effectiveness is net present value NPV (or net benefit equal to benefits minus the cost). However, the stochastic analysis also calculates the probability that an adaptation measure will have NPV>0, indicating the confidence level of adaptation effectiveness. An appropriate adaptation strategy may be one that increases design wind speeds for new houses leading to reduced vulnerability of new construction. The simulation analysis found that increasing the wind classification for design of new housing (at a cost of $3,700 per house) for all cities can produce a mean NPV that exceeds $8.3 billion by 2100 assuming a 4% discount rate (see Figure). The benefits are highest for Brisbane due to its high exposure (large population) and relatively high vulnerability of existing residential construction. Retrofitting older houses is a more costly adaptation strategy which mostly resulted in a net loss. We also showed that the benefits of adaptation strategies are maximised if they are implemented promptly, but deferral to 2020 or even 2030 will still result in a net benefit to society, albeit at a reduced level when compared to immediate implementation. The sensitivity of results to discount rate, including intergenerational effects, was studied. This will provide practical advice to policy makers to help ‘future proof’ built infrastructure to a changing climate.

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