Why are there so many 100-year storms?

It seems every time it rains heavily, people use this phrase.

The #climatechange predictions of increasing storm frequency and intensity seem accurate. That’s true.

But using the 100-year storm headline can be misleading.

You see, every location has a unique 100-year storm. Several, in fact.

The flow arriving at your house depends on lots of things:

  • The shape of the land

  • The size of the rainfall catchment

  • What the surface of the land is covered in

  • Your position in the catchment

  • How the rainfall changes during the storm

  • The storm duration

All these factors combine to produce a (not ‘the') unique 100-year storm for every house.

They’re all 100-year storms.

So during any very heavy rainfall, there is a pretty good chance that someone’s house experiences a 100-year event. So you can truthfully say we see 100-year storms all the time. Way more than once in a century. 

But at your coworkers house this weekend? It’s pretty unlikely.

Ian Warren