04 March 2022
This Guardian article 'Are eastern Australia’s catastrophic floods really a one-in-1,000 year event?' comments on the record breaking rainfall and catastrophic floods in Northern NSW in March 2022
The flooding was described by the Premier as a once-in-a-millennium (or “one-in-1,000-year event”) event. Most people would understand that to mean that scale of flooding won't be seen again this millennium, that it was not foreseeable, and that there is no need to plan for the next catastrophic storm.
The reality is it could come much, much sooner and the term “one-in-1,000-year event” has a specific meaning.
When employed in a technical report, it means there is a 0.1% chance of a flood of that severity happening in a given location in any given year. (For a one-in-100-year flood it’s a 1% chance, for a 1-in-10 year flood it’s a 10% chance, and so on.)
This article outlines that the chance of a catastrophic flood occurring somewhere in NSW, across all the areas at risk of flood in any given year, is much greater than 0.1%.