Clermont County has seen its fair share of large storm events recently, and the term “100-year rain” may be something you’ve heard frequently assigned to these events. But what does a “100-year” rainfall event actually mean, and how is it happening multiple times within a 100 year span?

It’s a common misconception that a 100-year event will happen once every 100 years. A 100-year rain is defined as the amount of rainfall for a specified location and duration that, on average, is exceeded once every 100 years. This means there is a 1% chance of a 100-year event every year. The NOAA’s National Weather Service estimates in the table below what constitutes a 100-year event for Clermont County.

In recent years, multiple “100-year” rainfall events have occurred within the same year. These trends suggest that the rainfall patterns we have traditionally used to describe extreme events are changing.

According to the Ohio Climate Office website, eight of the ten wettest years on record in Ohio have been after 1990. Precipitation is also arriving in fewer, but more intense, rainfall events which makes the chances of 100-year or larger events more common. Impacts that come with these larger rainfall events include challenges to agriculture, stormwater infrastructure, and public safety due to flooding.

So if it seems that there are more severe storms and flooding events than you remember growing up, you’d be correct. If you would like advice on water-related issues on your property, reach out to our office!