Groundwork Milwaukee and The New School’s Urban Systems Lab Release Launch The Milwaukee Flood Health Vulnerability Assessment

The assessment tool identifies communities across Milwaukee where exposure to urban flooding and pre-existing health, housing and socioeconomic conditions intersect and create disproportionate vulnerabilities to the impacts caused by extreme flooding

The city of Milwaukee is situated at the confluence of three rivers, atop wetlands and buried streams, and alongside Lake Michigan. As such, Milwaukee has developed its identity as a Water Centric City. However, a city that was built upon water is also vulnerable to it, particularly from extreme precipitation and flooding. Urban flooding can lead to loss of human life, damaged property, disruptions in public transport, and the deterioration of health conditions due to waterborne diseases. Moreover, these effects can be exacerbated by socioeconomic, health and housing conditions. These intersecting vulnerabilities are the focus of a new research study to understand the overlapping risks related to both health and urban flooding in the city of Milwaukee.

One of the key products developed through the study is The Milwaukee Flood Health Vulnerability Assessment (MFHVA) developed by the Urban Systems Lab,Groundwork Milwaukee and in partnership Wisconsin Health Professionals For Climate Action, and Data You Can Use. While Milwaukee has made bold steps to improve its capacity to handle stormwater, vulnerable communities are still disproportionately exposed to flooding. To highlight this concern, members of the Lab wanted to develop a map that explicitly considered environmental justice and social vulnerability together. Pablo Herreros Cantis, co-author of the MFHVA explains:

“We wanted to come up with a way to visualize something that has long been called for by local environmental justice organizations and communities, both generating new knowledge but also providing these organizations with robust arguments to support their already loud claims: that Milwaukee needs to prioritize neighborhoods that have been historically neglected by public investments, and that today are in urgent need of adapting to extreme weather events that are increasing due to climate change. During those initial conversations, we realized that despite both the critical impacts that flooding and stormwater can have on people’s health and the susceptibility of those with preexisting conditions to being negatively affected by flooding, the links between flooding and health are rarely considered when mapping social vulnerability. We were lucky to work with local healthcare practitioners affiliated with the Wisconsin Health Professionals for Climate Action group, who allowed us to dive into and helped process healthcare variables and datasets that we had never navigated before.”

In Milwaukee, the Federal Emergency Management Agency (FEMA) is responsible for generating crucial flood hazard maps that inform flood-related regulations. In the past, however, FEMA’s hazard mapping has focused disproportionally on coastal and riverine flooding and not pluvial flooding or inland flooding, despite urban areas being greatly susceptible to the latter. Pluvial flooding is caused by the flow of surface runoff when the built environment lacks the necessary pervious surface, like parks and natural areas, to absorb the amount of rain falling within a given period of time. This is common in urban areas due to the high concentration of impervious surfaces that prevents water from infiltrating into the ground. We incorporated pluvial flooding into the assessment by simulating a 100-year, 1- hour storm in the city of Milwaukee using a surface runoff model called CityCAT. The model computes the flow of water in real time accounting for infiltration based on the distribution of previous and impervious surfaces. We then evaluated what areas across Milwaukee are most exposed to flooding. We did this by calculating the percentage of total road and total residential units impacted by flooding per census tract. Finally, to generate the exposure index, we calculated the average value between both exposure scores in each census tract.

In order to see the ways in which exposure to flooding and exposure to social vulnerabilities overlapped, we considered the following indicators, then used census data to find which census tracts showcased these vulnerabilities:

Health Indicators:

• Percentage of adults having diabetes
• Percentage of adults reported having experienced poor mental health over the last 14 days
• Percentage of people having a disability, age adjusted ER rate due to asthma
• Percentage of adults without health insurance

Housing Indicators

• Percentage of residential units built before 1950
• Percentage of households without a car
• Percentage of households composed of a single adult living alone

Socio-economic Indicators

• Percentage of residents aged below 18 and above 65 years old,
• Percentage of people with a salary below twice the federal poverty line,
• Percentage of people aged above 25 without a high school diploma,
• Percentage of the population aged 5 and over who do not speak english,
• Percentage of residents self-identified as Black, Indigenous or Person of Color according to the US Census)

We found that almost 40% percent of Milwaukee’s population is vulnerable to one or the other, or both of these impacts. Moreover, where these indicators converge and overlap, they create disproportionate vulnerabilities to extreme flooding. A final social vulnerability index was generated by averaging the three scores related to social vulnerability and flooding exposure. aps developed through the assessment show the highest vulnerability values are concentrated in the city’s central tracts. While the MFHVA integrate index is useful in representing multiple kinds of vulnerability, the three categories used by the CDC and others (housing, health, socio-economic) may also be useful to identify specific challenges faced by the different communities in Milwaukee.

How can the MFHVA be used to advance Milwaukee’s equity and sustainability goals? Our hope is this data can be used to identify key vulnerability indicators within the census tracts and to support the development of tailored interventions when used in collaboration with local communities. The aim here is to provide critical information on both flood exposure and social vulnerability to support community-based advocacy and future planning to mitigate potential flood and health risks. Acknowledging the spatial injustice of urban flooding and the health impacts of storm events to Milwaukeeans will allow the City to further refine the prioritization of Green Infrastructure projects, ensuring they are benefiting those most in need of protection against dangerous flooding and water quality issues.

Left: Comparison between FEMA’s Special Flood Hazard Areas and pluvial flooding in Milwaukee based on a 1-hr, 100-year precipitation event. Pluvial flooding was considered when the maximum flooding depth surpassed 4 inches. Right: Flooding Exposure Index in Milwaukee, with scores sorted in quintiles.

Left: Health Vulnerability Index. Center: Housing Vulnerability Index. Right: Socioeconomic Vulnerability Index.

Social vulnerability and exposure indices (top) and the identified hotspots for each index (bottom.) Census tracts were considered as hotspots if their index value fell within the top quartile (top 25%.

Overlap between Flood Exposure and Social Vulnerability hotspots across Milwaukee.

In partnership with Groundwork USA, we also co-developed a Storymap to further illustrate our approach and the results of our study. A technical report is also available which provides a list of data sources, methods and background information on the project.

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This project is a collaboration between Groundwork Milwaukee, Wisconsin Health Care Professionals for Climate Action, Data You Can Use, The New School’s Urban Systems Lab, and Groundwork USA and is supported in part by the Kresge Foundation’s CREWS program, The JPB Foundation, and The Doris Duke Charitable Foundation. The views expressed here do not necessarily reflect the views of these foundations.

For inquiries about the project, you may contact Groundwork Milwaukee at young@groundworkmke.org and the Urban Systems Lab at urbansystemslab@newschool.edu.