It's not even amounts of rain that are necessarily the problem.

In my area, big rainstorms sometimes include hail, and if some of the hail/debris is big enough to block sewer grates, then the deluge of water will quickly sweep hail and other debris into the partial blockage until the grates are thoroughly clogged.

I'm not sure how you could adequately design against that while not having storm water grates that are hazardous to people/animals/etc.