A Conversation on Flooding

Aaron Fisher | December 19, 2023

It’s always exciting to learn something unexpected. That happened to me recently when I was chatting with Gabrielle Villarini about stormwater. His lab had taken the time to study the root cause of flooding events across the Upper Midwest.

This Advances in Water Resources study (On the statistical attribution of the frequency of flood events across the U.S. Midwest) basically said the single greatest predictor of flooding events is the volume of rainfall. Antecedent wetness (snowpack, prior rain) is of secondary import. Temperature, land use, and urban intensity are less important.

The surprising part was when looking at flooding events, impermeable cover did not make a big difference on flooding unless the area was highly urbanized. Impermeable cover has been one of the key points of focus of stormwater regulations. This report makes a strong argument that we may need to adjust our thinking to tackle the challenge head-on.

To be fair, this is not a radical rethink. In stormwater, we’ve historically focused on water quantity, with only recent detours into water quality concerns. We know how to do it, we’ve done it before, we just need our regulations to reflect the outcomes we desire.

Furthermore, if rainfall is the single biggest predictor of flooding, this is only going to become a bigger issue. Climate change is increasing the frequency of extreme rainfall events—increasing the chance of a flood.

But before you leave disheartened, the stormwater toolbox is numerous. There are a range of solutions that address rainfall quickly and in large volumes. At Ernest Maier we are partial to PaveDrain but know there is no single silver bullet to do it all.