1. Introduction
Pluvial flooding and sewer overflows comprise a multifactorial public health problem that raises risks for mortality and morbidity of a host of serious health conditions. Health impacts from flooding can be physical or psychological. Physical outcomes include gastrointestinal illnesses, respiratory illnesses, skin rashes and infections and poisoning from exposure to chemical irritants [
1,
2,
3,
4,
5,
6,
7]. Psychological distress and trauma are common among people who have experienced sudden flooding as a result of extreme weather events [
8,
9,
10].
Flooding impacts can be felt during or after the flooding event [
11]. Women, the elderly and small children are more likely to experience physical and psychological outcomes during floods whereas men are at high risk for mortality during and after flooding events [
12,
13,
14,
15,
16]. Intensity of flooding has a graded impact on physical and psychological health; long term psychological effects such as anxiety, depression and PTSD can occur for several years following a flooding event [
8,
17,
18,
19]. Flooding can cause serious disruptions to the provisions of mental health treatment exacerbating existing mental health problems in people who have them [
20]. Long term effects include trauma and stress-related problems as a result of displacement, economic insecurity and future housing uncertainty [
21]. Mortality has been found to increase in the months following major flood events [
22] and flooding impacts can be felt even by persons outside flooded areas through groundwater contamination [
23].
Home flooding is a serious public health problem that has long lasting health impacts for people who experience it [
24,
25,
26,
27,
28,
29,
30]. Microbial toxins such as molds and fungus are known to worsen respiratory problems and are associated with the development of asthma and allergic rhinitis [
31,
32]. Evidence from New Orleans, LA following Hurricane Katrina suggests that homes with experienced flooding were more likely to develop molds and fungus [
33]. Home dampness has been found to increase the severity of symptoms for a number of respiratory conditions, including asthma and chronic bronchitis and to increase exposure to numerous types of microbial agents [
34,
35,
36]
Climate and rainfall patterns in the Midwest region of the United States have been altered over the past five decades due to climate change [
37,
38]. Globally, urban land exposed to climate and flooding hazard risks is expected to increase by more than 25 percent compared with current levels [
39]. Natural hazards and extreme weather events have become more common and increasingly costly in the US over the past two decades, the costliest of which have impacted urban areas such as Detroit, MI [
40,
41,
42]. Changes in frequency and intensity of rainfall patterns can overwhelm aging infrastructure in challenged cities like Detroit, and create multiple stormwater issues [
43]. Natural hazards have been shown to worsen problems of economic inequality [
44]. Serious impacts from flooding are the result of a confluence of factors including extreme weather events, robustness of infrastructure and other factors to mitigate flood risk, housing conditions and individual level vulnerability [
45,
46]. Though significant effort has been directed to major flooding events (e.g., dam breaks, flood wave propagation), little work has been done on recurrent, localized pluvial and non-pluvial flooding in urban contexts.
The City of Detroit, MI, like many post-industrial cities, faces a wide range of converging challenges including population loss, demographic change and decades of financial and political neglect [
47]. As of 2020, Detroit’s population is approx. 670,000 people, down from a peak population of 1.6 million people in 1960 [
48]. Nearly 80 percent of Detroit residents are African-American. It is among the poorest of large cities in the US with a median household income of
$31,000, less than half of the state median income of
$72,000 [
48]. The City struggles to provide public services to its residents as a result of declining tax revenues, low levels of investment and decline of population density which forces Detroit to provide services using antiquated systems appropriate for a much larger population [
49].
A cross-sectional study of 164 homes in northwest Detroit indicated that 64% of homes experienced at least one flooding event in the past year, with many experiencing three or four events [
50]. Researchers of a small qualitative study reported on interviews with residents across the city, confirming that flooding was widespread with many potential risk factors, resources for prevention and recovery were uneven, and social, economic, and mental and physical health implications were extensive [
51]. The Detroit Office of Sustainability found that residents report that they experience flooding very often (13%), somewhat often (23%), and occasionally (32%) [
52]. Though extreme weather events such as that which caused major flooding in Detroit in 2014 have wide ranging acute impacts, recurrent household flooding may be an under-reported phenomenon in a city like Detroit and may be a problem that worsens with climate change [
53].
Detroit’s topography is mostly flat, with an overall change of only 33 m between its highest and lowest points. The City’s natural drainage is split between the Detroit and Rouge Rivers, though the natural tributaries were replaced with underground pipes prior to the 1960s. Water runoff and sewage flow through a combined system, discharging more than 58 million liters of treated and untreated sewage [
54] which eventually flows into Lake Erie. A result of Detroit’s combined system of rain runoff and sewage discharge is that large rain events can overwhelm the City’s treatment system, causing sewage backflow into homes during storm weather events [
55]. Communities along the Detroit River, most notably the Jefferson-Chalmers area, have historically experienced flooding events of various degrees. Aged housing stock, high prevalence of impervious surfaces and high prevalence of basements put Detroit residents at high risk for home flooding [
56].
Research Goals
Recurrent home flooding is an overlooked public health problem that presents a wide range of health risks to populations in economically challenged post-industrial cities like Detroit, Michigan. To inform prevention and recovery efforts, we first describe the extent and frequency of pluvial flooding in Detroit households using data from a house to house survey. As part of this effort, we identify particular locations or areas at high or low risk for household flooding events. Next, we use location information to link households to other data sets to test for associations of household and neighborhood/tract level determinants of household flooding events. Using the results of the first two aims, we create a multivariate model that could be used to predict flooding risk for individual households or households located within specific tracts or areas. Finally, we explore how flooding and factors associated with flooding might determine household asthma prevalence in surveyed households.
We hypothesize that flooding events are concentrated in specific areas and that households that experience flooding events are in proximity to other homes that experience flooding events. We hypothesize that both neighborhood and household level factors will determine pluvial flooding risk. We expect that no one factor in isolation determines household level flooding risk and create a multivariate regression model to predict flood risk using all available variables. Finally, we test the hypothesis that home flooding and factors associated with home flooding also determine household level public health outcomes such as asthma, which may result from exposure to chemicals, bacteria, or mold.
4. Discussion
Using a house-to-house survey of homes and residents throughout the city, we have shown that pluvial home flooding is a serious problem that impacts many Detroit residents. We found that while people all over Detroit experience home flooding, certain areas are at particular risk for flooding events. Renters and those living in areas where most homes are not owner occupied live at high risk for flooding. We found that poor housing conditions directly impact risk. When controlling for housing and neighborhood factors, we found that flooding disproportionately impacts communities of color. Finally, we found that flooding is associated with asthma risk in both adults and children.
Our results suggest that home flooding is a far more serious issue than previously thought, disproportionately impacting people who may lack financial means to effectively recover from flooding events and pluvial disasters, and who, due their status as renters, may lack the ability to implement measures to prevent or to mitigate the impacts of floods, such as basement weatherization or roof repairs. This would suggest that a focus on home flooding risk and efforts to improve housing quality should be a priority not only for advocates of urban housing, but also for public health organizations, focusing on programs that educate, work with, and provide resources to renters and incentives to landlords to improve housing quality/maintenance. Research in Germany has also suggested that directly communicating risks of flooding to home owners might encourage them to make improvements to prevent or mitigate flooding risk [
66]. Direct communication to landlords, for example, might encourage some to make necessary repairs and improvements to their properties.
We could find no similar studies that use expansive survey efforts to assess regular home flooding in urban areas. We did, however, find that the proportion of homes that experienced flooding in Detroit was in excess of the number of homes estimated to be at risk by other modelling efforts and higher than comparable cities in other Midwestern States [
67]. We recommend that surveys of home flooding be done to draw a distinction between flooding as a result of sudden, catastrophic weather events and the regular flooding that residents experience.
Our results indicated that household level factors were far stronger determinants of home flooding than neighborhood factors. Nearly all the household level variables such as basements in need of repair, mold on the walls and moldy smells, cracks in the walls and roof condition were significantly associated with flooding, both in univariate and multivariate analyses. Conversely, neighborhood level measures such as census tract level racial composition, poverty and environmental factors were not found to be associated with flooding. It is possible the low level of racial and socio-economic variation across Detroit prevents the detection of such associations. A study which included the surrounding, more affluent suburbs might have yielded a different set of results. However, our results indicate that within the City of Detroit, policy and intervention efforts which focus on home improvement, particularly for rental properties, might yield positive results.
We found that homes built after 1958 were less likely to have been flooded than home built before 1910, they were more likely to be flooded than homes built between 1910 and 1957. The history of building in Detroit has followed distinct waves of construction, following the city’s economic and social history. Nearly 40% of homes in Detroit were built in two decades prior to the Great Depression and many older homes in Detroit were originally of higher quality than homes which have since been demolished or unoccupied [
63]. This may explain the counterintuitive result that newer homes are more likely to be flooded than slightly older homes. Better built homes are usually spaced apart, set back from the street and have more pervious surfaces (yards) to absorb rainfall. Of course, there are exceptions. Homes in the Jefferson-Chalmers neighborhood, which were also built before the Great Depression, comprised a flooding “hot-spot” in our analyses due to its proximity to the river. Newer constructions must meet modern construction standards but comprise denser housing developments in formerly razed areas of the City. More work might be done to determine how housing quality and housing location intersect in the context of flooding risk.
A major limitation of this study was the measure of the flooding outcome. Reporting of flooding occurred only during the in-home visit by the survey team. Thus, flooding events long before the visit that were not in the recollection of the home occupant, and/or flood events after the survey visit were not recorded. Many homes that did not report flooding were visited prior to the city-wide flood of 2014 with the result that impacts from that event were not recorded for those households. Thus, the outcome measurement should be considered an underestimate. Compliance with survey projects is always a challenge. In the case of this study, certain biases should be assumed. For example, given that the present study was described as pertaining to housing conditions and flooding, we might assume that occupants of homes might be more likely to respond who experienced flooding or whose homes were in poor condition.
The flooding data collected also was not specific enough to make recommendations for specific interventions regarding household level flood mitigation. There are multiple causes of in-home flooding, including: sewer back-up, rising water levels of nearby waterways, ponded water around the home, rising groundwater levels around the home and subsequent leakage through foundation and basement, direct inflow through roof leaks, leaks of interior piping, and others. In many cases the flooding may stem from a variety of causes and problems. Future research efforts might ask residents to report incidence of recurrent home flooding to researchers or community leaders and teams could be dispatched to collect detailed information on sources and outcomes.
Detroit experiences the highest health impacts of asthma in Michigan, with the adult asthma rate 29% higher and the rate of asthma-related hospitalizations three times greater than the state average [
68]. In-home triggers account for 40% of all asthma episodes [
69]. Detroit has been called the “Epicenter of the Asthma Burden,” with at least 11.3% of Detroit children and 15.5% of Detroit adults having diagnosed asthma [
70]. We could not find data on household level prevalence of adult asthma but more than three quarters of the homes included in this study had at least one adult with asthma. We found that homes with asthmatic residents were more likely to be flooded. Based on this survey, we cannot conclude that there is a causal link between flooding and asthma. We can, however, conclude that persons with respiratory conditions such as asthma are more likely to live in homes that have been flooded.
Asthma has been associated with flooding in other studies, principally though the development of and exposure to molds and fungus within the home [
30,
31,
32]. Most research on the associations of flooding and health focus on extreme weather events such as Hurricane Katrina in New Orleans, LA [
71] and Hurricane Sandy in New Jersey [
72]. Regular flooding such as that which occurs in Detroit, however, might be causally associated asthma due to persistent mold problems in the home and constant exposures to molds, fungus and other endotoxins. We note that the high baseline prevalence of asthma in Detroit and the lack of past data on asthma incidence and prevalence complicate efforts to assess causal links between flooding and asthma.
Future studies of this kind could focus on the public health impacts of recurrent flooding in households and how home improvement measures can be implemented as a means of reducing risk for serious health problems. Using a crude measurement of asthma prevalence, our research suggested that housing quality and flooding risk were associated with asthma in both adults and children. Future research should work to better characterize the public health impacts of regular flooding by implementing programs that improve housing conditions, such as basic measures to prevent basement leakage, while looking at basic health indicators. Evidence might suggest that asthma incidence or in asthma related health events decrease after implementing basic improvements such as sealing basements or preventing sewer backflows, which could lead to creative policy that treats home improvements as protecting the public health.
Future survey work should attempt to validate the results of this research. It should also be designed to better understand the causes and outcomes of regular flooding in Detroit. These efforts should be conducted on a regular basis, but should also mobilize during or after times of intense precipitation or known flooding events. Any survey work should also collect quantitative data such as high water mark and source location, and also collect detailed information on individual, home and neighborhood conditions that might contribute to flooding. Future studies might assess these factors over time and test for association with climate and rainfall patterns for forecasting and prediction. Qualitative information on residents’ experiences and ideas could help inform community and government efforts to mitigate flood and support flood victims. The often overlooked public health implications of regular flooding should, however, be a major focus of future research work to ensure equitable prevention and response.
