'One-in-100-years' flood talk disastrously misleading and should change, risk experts say

By Ben Deacon

• A one-in-100-year flood has a 1 per cent chance of occurring any year
• Town planners use one-in-100-year floods to decide where housing can be built
• One-in-100-year floods are probably not becoming more common in NSW

What does it mean when a natural disaster is described as a "one-in-50-years" or "one-in-100-years" event? Well, not what most people think and that has to change, according to a leading risk assessment expert.

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"It gives a false sense of security really, that if you experience a flood to that magnitude, then you're OK, because you've got another 100 years to wait until that event is likely to occur again. And that's certainly not the case," he said.

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So is the kind of rainfall that causes 100-year flood events becoming more common and is this evidence of climate change?

Probably not, according to Dr Andrew King, from the ARC Centre of Excellence for Climate Extremes at the University of Melbourne.

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Unplanned urbanization creates greater risk of floods which displace more people than many conflicts.#MCR2030 #ResilientCities https://t.co/LunG9bW7US pic.twitter.com/pugKjdeo7Y

— UNDRR (@UNDRR) March 28, 2021