Wisconsin's climate is changing. Wisconsin's cities and towns must also change how they manage their water resources if they are to adapt to the increases in rainfall and groundwater elevation we are already seeing. The Stormwater Working Group has brought together Wisconsin water resource managers to find ways to reduce risk to our communities and improve our stormwater management infrastructure.

Potential Risks

car driving on flooded street

Photo by David Liebl

Recent analysis of historical data, combined with climate model downscaling, suggest that the southern Wisconsin precipitation events of 2008 are part of a trend toward wetter conditions and more intense rainfall. Climate models also suggest that increased winter snow pack, and late winter rainfall, may result in high regional groundwater tables and lake levels, and saturated soil conditions.


Local and state government and private sector developers make significant investments in long-lived infrastructure that controls or is affected by stormwater runoff from large rainfalls. Likewise, municipal waste water treatment plant operators make substantial long-term investments in their system capacity that anticipates development, but not increased stormwater inflow and groundwater infiltration. This infrastructure is designed using standards based on rainfall data from the latter half of the 20th century. By having assumed“stationarity” of climate in the design of our infrastructure, we are now vulnerable to the following impacts from more intense rainfall events and elevated groundwater:

house with yard flooded

Photo by Madeline Gotkowitz

  • Conveyance systems filled beyond capacity cause flooded homes and urban streets;
  • Roadways and bridges are washed-out or become impassable;
  • Groundwater flooding of property and cropland increases;
  • Rural residential wellheads are contaminated by flood waters and high groundwater;
  • Impoundments and stormwater detention ponds fail more frequently;
  • Raingardens and other biofiltration BMPs fail due to saturated soil conditions;
  • Increased erosion of slopes by intense rainfall events leads to high sediment and phosphorus loading to surface waters;
  • Runoff of manure from fields, and accompanying fish kills, are more frequent;
  • Storm water inflow and groundwater infiltration to sanitary sewers, results in untreated municipal wastewater flowing into to lakes and streams.

In summary, our previous investment in public safety and environmental protection risks being overwhelmed by precipitation impacts that are beyond those anticipated by past infrastructure designers and water resource managers.

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Data Needs

While recent analysis of regional climate and rainfall data have provided insights into changes in climate over the last several decades, our ability to anticipate future conditions, and adopt appropriate adaptation strategies, will require more and better data about precipitation in Wisconsin. For example:

  • The resolution of weather data needs to be improved (finer geographic scale) to be able to support both predictive climate modeling, and rainfall/runoff impact modeling.
  • Accurate measurement of localized rainfall amounts is essential for managing and maintaining storm water best management practices (BMPs).  Calibrated radar rainfall data that can account for rainfall amounts at the sub-watershed or catchment level would allow runoff flows to individual conveyances and BMPs to be estimated.
  • The ability to measure antecedent soil moisture and groundwater conditions is necessary for predicting the severity of flooding and stormwater impacts.   However, the data gathering capacity of the state stationary groundwater monitoring system is at risk due to lack of funding.
  • Stormwater and wastewater mangers need better tools for modeling future runoff, soil moisture and groundwater conditions if they are to adapt to increases in precipitation.

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Adaptation Strategies

There is a growing consensus that scientific knowledge about the potential increase in magnitude and frequency of large rainfalls is sufficient to warrant immediate changes in the methods used to design and manage storm water-related infrastructure. For example, the following steps have been identified by the Stormwater working group:

flooded cemetary

Groundwater flooding, Spring Green, WI
Photo by Peter Gorman

  • Synthesize existing historical and model data for rainfall in the upper Midwestern U.S. to provide a more accurate account of current and future precipitation;
  • Use a risk/consequence approach to evaluating and modifying existing infrastructure to accommodate observed and predicted changes in climate.
  • Develop and evaluate alternative tools and strategies for the design of storm water-related infrastructure, using a collaborative process that includes climate scientists, water resource managers, design engineers, and regulators, and members of relevant business communities;
  • Communicate findings and recommendations to water resource managers, design engineers, relevant government entities and other decision makers.

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Please contact Ken Potter or David Liebl if you have any comments or concerns regarding Wisconsin's stormwater and our changing climate or if you would like to have someone from the Stormwater Working Group make a presentation to your group or town.