The 100-year storm. The 50-year flood. We've been hearing these terms a lot over the last few years. Common understanding is that they are events that happen once every 100 years. Or once every 50 years. In reality, they are events that have a 1% (or 2%) chance of happening every year. Lately, we've been beating the odds on major rainfall events in Ontario. These events increase the impacts of seasonal flooding and make exceptional or extraordinary flooding more likely and often more damaging.