I drew this cartoon in response to a news report describing a recent flood as a one in one hundred year event. It reminded me of just how poor our understanding of probability is and how unhelpful describing a flood (or anything for that matter) as a one in (whatever the number of year’s) event. In a sense this cartoon is in itself inaccurate as a one in one hundred year flood does not mean there will be only one such flood every one hundred years, back in 1893 Brisbane had two floods that could be described as one in one hundred year floods within weeks of each other. A better way of describing a one in one hundred year flood is saying that such a flood has a 1% chance of occurring in a given year. But if floods of a certain height in a given location are happening on average every twenty years than such floods have a 5% chance of occurring in a given year. We would have a better understanding of probability if the percentage chance of a flood occurring was quoted instead of describing it as a one in (whatever the number of year’s) flood.
CARTOON REFERENCE NUMBER: 2026-08