Climate change increases the risk of natural disasters by increasing the intensity of the hazards and widening their distribution. Obvious examples are tropical cyclones, bushfires, floods and droughts. The impact of tropical cyclones will be further exacerbated by rising sea levels. Historically for Australia the ranking severity of disaster impact would be bushfires, windstorms and earthquakes in the south and tropical cyclones, bushfires and earthquakes in the north.
We have a lower level of acceptable risk for events with a higher loss of life and for buildings and infrastructure which have key post disaster functions – emergency service centres, hospitals, schools, community centres. These levels of acceptable risk are not sufficiently articulated in codes of practice. A good example of acceptable risk of loss is found in the Australian National Committee on Large Dams Guidelines, where the acceptable annual probability of loss of 100 lives or more in a dam “failure” is 1 x 10-6. We build up our best practice on precedence over the past 200 years, using mathematical and physical models to stretch out the application over 500 years (for typical structural design). We have to stretch out the application to 5000 years or more – a “known unknown” exacerbated by climate change, another “known unknown”.
A globally accepted figure on the cost of disasters is that $1 spent before disaster strikes is as effective in saving lives and building community resilience as $7 spent after disaster strikes. Typically after a disaster the community rebuilds to a higher standard of resilience, based upon improved scientifically based principles. However, all those regions lucky to escape recent disasters remain vulnerable. Instead of retrofitting we rely on obsolescence and replacement for gradual renewal. Meanwhile, thanks to climate change we are renewing to a standard already becoming obsolete.