There are currently 273,400 properties in Wisconsin that have a substantial risk of flooding, according to a new report from the First Street Foundation, a nonprofit that studies flood risks.
The First Street Foundation estimate is 1.9 times higher than what FEMA says is the number of vulnerable properties in the state. FEMA’s Flood Insurance Rate Maps identify 144,000 properties that are at substantial risk of flooding.
The First Street report says that this problem is only going to get worse as climate change continues. By 2050, the report estimates, the number of properties at substantial risk will increase by nearly 3% — to 281,100.
Substantial risk means that every year, the property has at least a 0.2% risk of water from a 100-year flood reaching the building or lot.
Nationally, the First Street data finds that 14.7 million properties are at substantial risk, compared to 8.7 million properties in the government maps.
The difference takes into account rises in sea-level and increased precipitation caused by climate change. It also includes some bodies of water, such as small creeks, that are not mapped by the government. Accounting for a changing climate is important because in many places, increased flooding will likely be the most devastating impact.
“In environmental engineering, there is a concept called stationarity, which assumes that today is going to be like yesterday, and tomorrow is going to be like yesterday,” Dr. Ed Kearns, First Street Foundation’s chief data officer, said in a statement. “This concept used to work, but with a changing environment it’s a poor assumption and no longer does. FEMA’s method assumes stationarity, First Street’s does not.”
Wisconsin’s overall risk is not expected to rise as much as the country at large, the report states. The U.S. flood risk is expected to increase from 10.3% of properties to 11.4%, according to the report. Wisconsin’s risk is expected to increase from 8.1% to 8.3%.
But less risk doesn’t matter much once someone’s home is underwater and the properties with substantial risk in Wisconsin are spread across the state.
The municipalities with the greatest number of properties at risk are Milwaukee and Madison. Milwaukee has 12,203 at-risk properties while Madison has 5,755.
But proportionally, the municipality most at risk — by far — is the City of Oconto. A total of 1,351 of the city’s properties are at risk, which is 58% of the city, according to the report. Oconto’s percentage is 21 points higher than the second most at risk city, Lake Wisconsin.
The municipality most susceptible to climate change-caused flooding is Milton. By 2050, the number of at-risk properties in the city will increase by more than 20%.
While Wisconsinites have faced flooding in the past, the First Street report suggests more people will be susceptible in the future. However, the report does say there are actions individuals and governments can take.
Individuals can work to flood-proof their homes and take out flood insurance. Governments, the report says, should invest in infrastructure that limits the potential damage. Every dollar spent on flood risk reduction saves seven dollars on future disaster losses, according to the report.