Wisconsin has had a June full of flash floods and mudslides. How concerned should we be?
It was another wet night for much of southern Wisconsin, and more rain is in the forecast. Flood warnings are out along many rivers and streams, including in Kenosha and Racine County.
Flash flood warnings are also in effect around Madison and just to the south and west of Kenosha, while flash flood watches are posted for much of the southern half of the state - though not Milwaukee or Waukesha County at this point.
The rainfall numbers have been impressive to date. In Milwaukee, we've now had more than 24.5 inches of precipitation this year, and Madison reports even more.
"Rainfall is a tricky thing to understand, largely because what controls the variation of rainfall over long periods of time isn't fully understood," says Kenneth Potter, a professor of civil and environmental engineering at UW-Madison.
An expert on flooding and storm water management, Potter says our recent heavy rains rival the historic storms Wisconsin experienced back in the late 1800s, which flooded the Mississippi River and the Great Lakes.
The difference now, Potter says, is "we have more people in more vulnerable situations - for example, we've urbanized further."
"The increase in flooding that results when one converts soil to impervious surfaces such as concrete or asphalt or rooftops, causes great increases in the magnitude of floods, particularly in flash flooding," he says. "A lot of time, the drainage areas are small, so there is really nothing we can do worse than urbanize in terms of increasing floods, so the key is how we manage that increase in run-off."
Potter says Wisconsin leads the nation in green infrastructure that helps deal with storm water, such as rain gardens and roof gardens. But he says Wisconsin hasn't done a good job in dealing with storing and detaining large rain events.
"There are no state rules in Wisconsin regarding control for large events," he says. "All the rules that control large events, and in particular construction of...large detention ponds, all those rules are local...There really needs to be a state wide ordinance."
That's because Potter doesn't think the rules many municipalities and counties have go far enough. He says their storm water storage could only handle the kind of flooding event that might occur once every ten years. Instead, Potter argues they should protect against the major floods that might happen every 100 years.
"We know that the 100-year flood is what causes the serious damage, so I think that's a big gap in our regulatory structure in Wisconsin," he says. "It's something that we need to address, both in terms of urbanization, but also remember that climate is changing and we are going to see bigger events and more of them."
Potter says theoretical and data-based evidence show that changes in global climate, due to increasing green house gases, will increase the number and intensity of storms in the future. So flooding levels like what Wisconsin is seeing now will become more frequent.
But Potter says there are some positives to all the rain, given there are some droughts around the state.
"We do have water shortages, believe it or not, in parts of the state because of excessive pumping, so it's good that we're recharging ground water," he says.
That said, Potter explains that heavy rains don't recharge the water supply as well as snow melt or precipitation during the fall and winter months when there is less evaporation.