Wisconsin’s Infrastructure is Increasingly at Risk Due to Extreme Rainfall

Contact the authors

Daniel Wright, assistant professor, Department of Civil and Environmental Engineering, UW–Madison, danielb.wright@wisc.edu

Robert Montgomery, Emmons & Olivier Resources, Inc., and UW–Madison, rmontgomery2@wisc.edu

“Ten-year” and “100-year” storms, as measures of extreme rainfall, are used to design much of our civil infrastructure, including bridges, culverts, storm sewers, detention ponds, and dams. The first nationwide analysis of these storms dates from a 1961 publication by the US Weather Bureau called “Technical Paper 40.” The National Weather Service released updated results for the Midwest in “Atlas 14” Volume 8 in 2013. Atlas 14 included an additional five decades of data collected since 1961, a time period which saw substantial increases in rainfall depth and frequency — see Figure 1.

These increases translated into upward revisions of the analyses. In Madison, Wisconsin, for example, the 24-hour, 100-year storm increased from about 6.0 inches of rainfall in Technical Paper 40 to about 6.6 inches in Atlas 14. Climate change is the most likely culprit.

Rainfall extremes continue to increase in frequency and amount. Our recent research shows that Atlas 14 is already out of date over much of the country, seriously understating current levels of extreme rainfall. The RainyDay software we developed at UW-Madison provides a fast, low-cost option for improving upon Atlas 14 by drawing on recent storms from around the state.

The chart shows that west Madison has gone from one to two days per year of more than 2 inches of rain.
Figure 1: The number of days per year, 1961 through 2018, that had greater than 2 inches of rain in west Madison. The frequency of such days has doubled over this time. View a larger version of this graphic
The chart shows discrepancies between Atlas 14 and RainDay software.
Figure 2: 100-year 24-hour storm rainfall depth projections from NOAA Atlas 14 (left) and RainyDay software (middle). The difference between the two is shown on the map on the right. View a larger version of this graphic

It does so using weather radar, which can observe rainfall patterns over large areas, as opposed to at individual locations like conventional measurements. These improved predictions, illustrated in Figure 2, are now being utilized by several local municipalities for stormwater and floodplain analysis.

Current projections from other UW researchers suggest that today’s 100-year storm may occur five times more often by the end of the 21st century. Because water infrastructure is built to last 50 years or more, continued rainfall intensification means that our infrastructure will become more and more vulnerable and inadequate as it ages.

We seek to use the best available techniques to project rainfall changes for the next 50 to 100 years. This will help engineers to make more resilient designs, operations, and maintenance plans. Up-to-date analyses of rapidly changing extreme rainfall events are needed in order to protect Wisconsin’s infrastructure, communities, and economy.

Learn More About Extreme Precipitation Research at UW-Madison