Beware those black swans

We recently experienced an event involving an extended period of heavy rain over a short period of time which caused widespread flooding across much of New Zealand's lower North Island. Personally we were unaffected although many here in the Rangitikei were not so lucky, with water through their homes. While in Wanganui much infrastructure and property was damaged as the river overflowed banks. As the debate continues about whether this is a '100 year event' or 'a new norm' as part of global warming, I am reminded of our human need to be able to explain such events. We often assume that such events can be explained in a linear way - statistically speaking a 'normal' distribution. We all rely on being able to assess the risk of certain events occurring assuming such events are normally distributed. Are we sure that the world works this way?

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