Extreme Rainfall and Native Prairies

Contact the authors

Paul Zedler, associate director for research and education, professor emeritus, Nelson Institute for Environmental Studies, UW–Madison, phzedler@wisc.edu

Brad Herrick, ecologist, research program manager, UW–Madison Arboretum, bradley.herrick@wisc.edu

In May and early June of 2008, a large region in south central Wisconsin, which included most of the drainage area of the Crawfish River, experienced a series of extreme rainstorms. Three unusual June rainfalls recorded at Beaver Dam/Westport had a cumulative total of 30.2 centimeters (11.9 inches) and were the fourth, fifth, and ninth highest daily rainfall events out of the 10,649 events recorded from 2008 to 2019 at that site. This rain fell on a landscape that was already near saturation due to high rainfall and flooding in the autumn of 2007 followed by high snowfall in the winter. The result was a massive flood that peaked in June and slowly receded into July.

What made the 2008 flood notable was not only its historical extreme, but the fact that it occurred well into the growing season, which caused it to devastate large areas of recently planted agricultural crops. The average monthly flow for June 2008 is still the greatest recorded at the U.S. Geological Survey (USGS) Milford gauging station since records began in 1931.

Our focus is on the effect of the flood on Faville Prairie, an unplowed remnant managed as a biodiversity reserve by the University of Wisconsin-Madison Arboretum. It is a site of importance in the history of conservation. In the 1930s, Aldo Leopold and his students conducted extensive studies on the then largely undisturbed “Crawfish Prairie.”

Much of the Faville Prairie was under three feet of water as a result of the extreme storms of 2008.
An aerial view of the flooded Faville Prairie. Photo courtesy of Paul Zedler.

At the time, the losses of wild prairies and wetlands were ramping up dramatically as farm fields were created by drainage using ditches and subsurface tiling. Leopold’s essay “Exit Orchis,” lamenting the loss of this pristine wetland prairie complex, prompted a private citizen to buy and donate land for a 92-acre fragment that is now the Faville Prairie.

Did these extreme events, which produced flooding to a maximum depth of over a meter and persisted for weeks, do significant damage to this important remnant? When the waters abated, a few species emerged green and growing, but the above-ground parts of many more species were dead. However, by the end of the 2008 growing season, most species had recovered by resprouting. Tradescantia ohiensis (spiderwort) rebounded and flowered in profusion.

Populations of several other iconic prairie species, though, were drastically reduced, such as Silphium terebinthinaceum and S. laciniatum (prairie dock and compass plant). Dodecatheon meadia (shooting star) seems to be extinct on-site.

Our conclusion is that if a flood like this recurs more often than every 50 years, this highly vulnerable remnant prairie will not survive with its full complement of species. We would expect the site to gradually degrade and to become impoverished in native species, enriched in invasive exotics — a victim of the shift in flood timing and increased rainfall intensity.

Learn More About Extreme Precipitation Research at UW-Madison