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The Effects of Historical Housing Policies on Resident Exposure to Intra-Urban Heat: A Study of 108 US Urban Areas

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The increasing intensity, duration, and frequency of heat waves due to human-caused climate change puts historically underserved populations in a heightened state of precarity, as studies observe that vulnerable communities—especially those within urban areas in the United States—are disproportionately exposed to extreme heat. Lacking, however, are insights into fundamental questions about the role of historical housing policies in cauterizing current exposure to climate inequities like intra-urban heat. Here, we explore the relationship between “redlining”, or the historical practice of refusing home loans or insurance to whole neighborhoods based on a racially motivated perception of safety for investment, with present-day summertime intra-urban land surface temperature anomalies. Through a spatial analysis of 108 urban areas in the United States, we ask two questions: (1) how do historically redlined neighborhoods relate to current patterns of intra-urban heat? and (2) do these patterns vary by US Census Bureau region? Our results reveal that 94% of studied areas display consistent city-scale patterns of elevated land surface temperatures in formerly redlined areas relative to their non-redlined neighbors by as much as 7 °C. Regionally, Southeast and Western cities display the greatest differences while Midwest cities display the least. Nationally, land surface temperatures in redlined areas are approximately 2.6 °C warmer than in non-redlined areas. While these trends are partly attributable to the relative preponderance of impervious land cover to tree canopy in these areas, which we also examine, other factors may also be driving these differences. This study reveals that historical housing policies may, in fact, be directly responsible for disproportionate exposure to current heat events.
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climate
Article
The Eects of Historical Housing Policies on Resident
Exposure to Intra-Urban Heat: A Study of 108 US
Urban Areas
Jeremy S. Homan 1, 2, * , Vivek Shandas 3and Nicholas Pendleton 1,2
1Science Museum of Virginia, Richmond, VA 23220, USA; pendletonnv@mymail.vcu.edu
2Center for Environmental Studies, Virginia Commonwealth University, Richmond, VA 23220, USA
3
Nohad A. Toulan School of Urban Studies and Planning, Portland State University, Portland, OR 97201, USA;
vshandas@pdx.edu
*Correspondence: jhoman@smv.org
Received: 5 November 2019; Accepted: 3 January 2020; Published: 13 January 2020


Abstract:
The increasing intensity, duration, and frequency of heat waves due to human-caused
climate change puts historically underserved populations in a heightened state of precarity, as studies
observe that vulnerable communities—especially those within urban areas in the United States—are
disproportionately exposed to extreme heat. Lacking, however, are insights into fundamental
questions about the role of historical housing policies in cauterizing current exposure to climate
inequities like intra-urban heat. Here, we explore the relationship between “redlining”, or the
historical practice of refusing home loans or insurance to whole neighborhoods based on a racially
motivated perception of safety for investment, with present-day summertime intra-urban land surface
temperature anomalies. Through a spatial analysis of 108 urban areas in the United States, we ask two
questions: (1) how do historically redlined neighborhoods relate to current patterns of intra-urban
heat? and (2) do these patterns vary by US Census Bureau region? Our results reveal that 94% of
studied areas display consistent city-scale patterns of elevated land surface temperatures in formerly
redlined areas relative to their non-redlined neighbors by as much as 7
C. Regionally, Southeast
and Western cities display the greatest dierences while Midwest cities display the least. Nationally,
land surface temperatures in redlined areas are approximately 2.6
C warmer than in non-redlined
areas. While these trends are partly attributable to the relative preponderance of impervious land
cover to tree canopy in these areas, which we also examine, other factors may also be driving these
dierences. This study reveals that historical housing policies may, in fact, be directly responsible for
disproportionate exposure to current heat events.
Keywords: urban heat islands; environmental justice; climate change; redlining
1. Introduction
No other category of hazardous weather event in the United States has caused more fatalities
over the last few decades than extreme heat [
1
]. In fact, extreme heat is the leading cause of
summertime morbidity and has specific impacts on those communities with pre-existing health
conditions (e.g., chronic obstructive pulmonary disease, asthma, cardiovascular disease, etc.), limited
access to resources, and the elderly [
2
4
]. Excess heat limits the human body’s ability to regulate
its internal temperature, which can result in increased cases of heat cramps, heat exhaustion, and
heatstroke and may exacerbate other nervous system, respiratory, cardiovascular, genitourinary, and
diabetes-related conditions [
5
]. As heat extremes in urban areas become more common, longer in
duration, and more intense across the US and globe [
6
,
7
] due to unmitigated human emissions of
Climate 2020,8, 12; doi:10.3390/cli8010012 www.mdpi.com/journal/climate
Climate 2020,8, 12 2 of 15
heat-trapping gases from fossil fuels [
8
] as well as urban expansion [
9
], the number of deaths and
attendant illnesses are expected to increase around the US [10].
Urban landscapes amplify extreme heat due to the imbalance of low-slung built surfaces to natural,
non-human manufactured landscapes [
11
,
12
]. This urban heat island eect can cause temperatures
to vary as much as 10
C within a single urban area [
13
], even without comparison to a “traditional”
rural baseline for assessing UHI. Others, including Li et al. (2017), found that the density of total
impervious surface area (ISA) is a major predictor for land surface temperatures, or the “surface urban
heat island” studied here [
14
]; yet others describe the apparent cooling eects of urban green spaces.
In general, greenspace, trees, or water bodies within a city have been correlated with cooler land
surface temperatures (LST), and more greenspace or water is related to lower urban LST at the location
of that greenspace [
15
18
]. Hamstead et al. (2016) studied the role of landscape composition on surface
temperatures by dividing New York City into 22 classes at 3-m resolution and identifying the specific
ranges of land surface temperature represented within each class [
19
]. The authors conclude that urban
areas contain discernable “classes” of form—the integration of land use and land cover—and that
those sets have “distinct temperature signatures”.
Emerging research suggests that many of the hottest urban areas also tend to be inhabited
by resource-limited residents and communities of color [
20
,
21
], underscoring the emerging lens of
environmental justice as it relates to urban climate change and adaptation. In one study, Voelkel and
others (2018) found that residents living in neighborhoods with higher racial diversity, extreme poverty,
and lower levels of formal education were statistically more likely to be exposed to greater heat—the
neighborhood heat eect [
21
]. Still other studies have found that those with the least access to resources,
more advanced in age, and people with pre-existing face some of the greatest burden [
22
]. While the
evidence about the distributional implications of heat waves mounts, we still do not have a clear uniting
principle to explain consistent patterns between an emerging challenge like intra-urban heat and
observable records of excess mortality and morbidity among underserved populations. If heat varies
across urban environments, then why are communities of color and resource-limited communities
living in the hottest areas? Could a plausible explanation be the presence of past urban planning
programs and housing policies that have heightened disproportionate exposure to intra-urban heat in
US cities?
The present study further examines the relationship between present-day spatial patterns of
inequitable exposure to intra-urban heat and historical housing policies, which were applied to many
US cities in the early 20th century. We specifically examine maps generated by the Home Owners’ Loan
Corporation’s (HOLC) practice of “redlining” [
23
,
24
] in the 1930s. As part of a national program to lift
the US out of a recession, HOLC refinanced mortgages at low interest rates to prevent foreclosures, and
in the process created color-coded residential maps of 239 individual US cities with populations over
40,000. HOLC maps distinguished neighborhoods that were considered “best” and “hazardous” for
real estate investments (largely based on racial makeup), the latter of which was outlined in red, leading
to the term “redlining.” These “Residential Security” maps reflect one of four categories ranging from
“Best” (A, outlined in green), “Still Desirable” (B, outlined in blue), “Definitely Declining” (C, outlined
in yellow), to “Hazardous” (D, outlined in red), relating directly to subsequent access to mortgage
lending and at least partially to the racial makeup of that neighborhood.
Though redlining was banned in the US as part of the Fair Housing Act of 1968, a majority of
those areas deemed “hazardous” (and subsequently “redlined”) remain dominantly low-to-moderate
income and communities of color, while those deemed “desirable” remain predominantly white with
above-average incomes [
24
]. Those living in redlined areas experienced reduced credit access and
subsequent disinvestment, leading to increased segregation and lower home ownership, value, and
personal credit scores, even when compared to those similar-sized US cities that did not receive a HOLC
map [
23
]. Increasingly evident is the legacy of these historic policies in racial disparities in health
care, access to healthy food, incarceration, resources allotted for schools, and public infrastructure
Climate 2020,8, 12 3 of 15
investment such as the privileging of the suburban highway system at the expense of the city’s public
transportation [25].
Similarly, as areas that received severely limited real estate investment over time, we might
expect those areas to have fewer environmental amenities that help to clean and cool the air, including
urban tree canopy [
26
]. Recent studies describe the increased likelihood that those who are poor and
communities of color are more likely living in areas with fewer trees and poorer air quality [
27
,
28
].
At the same time, the extent to which these policies may have resulted in environmental disparity as a
consequence of systematic disinvestment nationally largely remains an open question. We seek here
to assess if evidence of disproportionate environmental stressors (specifically anomalous urban land
surface temperatures) exists through the lens of these long-term housing policies, and if a national-scale
signal varies by region in the US.
By assessing HOLC maps from aggregated urban areas in the United States (Figure 1) in relation
to the relative anomaly of land surface temperature within and outside redlined areas, we ask two
questions: (1) do historical policies of redlining help to explain current patterns of exposure to
intra-urban heat in US cities? and (2) how do these patterns vary by geographic location of cities?
Our intent is not to explain why precisely these patterns exist; instead, we seek to describe their
relation through spatial analysis of historical redlining maps and present-day warm season intra-urban
land surface temperature anomalies. By examining these patterns, we aim to assess how current
patterns of intra-urban heat inequities may result from a combination of historical policies that may be
further exacerbated by present-day planning practices that fail to center communities that have been
historically underserved in adaptation and mitigation of these patterns.
Climate 2020, 8, x FOR PEER REVIEW 3 of 15
including urban tree canopy [26]. Recent studies describe the increased likelihood that those who are
poor and communities of color are more likely living in areas with fewer trees and poorer air quality
[27,28]. At the same time, the extent to which these policies may have resulted in environmental
disparity as a consequence of systematic disinvestment nationally largely remains an open question.
We seek here to assess if evidence of disproportionate environmental stressors (specifically
anomalous urban land surface temperatures) exists through the lens of these long-term housing
policies, and if a national-scale signal varies by region in the US.
By assessing HOLC maps from aggregated urban areas in the United States (Figure 1) in relation
to the relative anomaly of land surface temperature within and outside redlined areas, we ask two
questions: (1) do historical policies of redlining help to explain current patterns of exposure to intra-
urban heat in US cities? and (2) how do these patterns vary by geographic location of cities? Our
intent is not to explain why precisely these patterns exist; instead, we seek to describe their relation
through spatial analysis of historical redlining maps and present-day warm season intra-urban land
surface temperature anomalies. By examining these patterns, we aim to assess how current patterns
of intra-urban heat inequities may result from a combination of historical policies that may be further
exacerbated by present-day planning practices that fail to center communities that have been
historically underserved in adaptation and mitigation of these patterns.
Figure 1. Map of 108 US cities with HOLC Residential Security maps included in this study. These
areas may include several smaller-area HOLC maps that have been aggregated into a larger urban
area (Supplementary Materials I).
2. Materials and Methods
We use the University of Richmond’s Digital Scholarship Lab’s “Mapping Inequality” database
(Figure 2a, Richmond, VA, USA, [29]) to download each available city’s HOLC map shapefile
individually (n = 239). To make analysis of Landsat-derived LST maps less computationally complex,
we then condense the 239 unique HOLC maps into a database of 108 US cities or urban areas that
overlap within Landsat 8 imagery tiles, and excluding any cities that were not mapped with at least
one of all four HOLC security rating categories (n = 4). In some cases, HOLC map shapefile
boundaries needed to remove overlapping security rating boundaries, boundary crossings over
bodies of water, and to merge overlapping maps drawn in the same generalizable urban area and/or
because they were drawn during different years (Supplementary Materials I).
We assess patterns of intra-urban land surface temperatures in the 108 HOLC areas using
readily-accessible Landsat 8 satellite-derived northern hemisphere summertime (June–August) land
surface temperatures (LSTs) following accepted United States Geological Survey calculation protocol
(30 × 30 m resolution, TIRS Band 10, Normal Difference Vegetation Index [NDVI] emissivity corrected
LST, Figure 2b [20,30,31]. This LST method relies on transforming raw Landsat 8 TIRS Band 10 data
into top-of-atmosphere spectral radiance and then into at-sensor brightness temperatures. LST is then
Figure 1.
Map of 108 US cities with HOLC Residential Security maps included in this study. These
areas may include several smaller-area HOLC maps that have been aggregated into a larger urban area
(Supplementary Materials I).
2. Materials and Methods
We use the University of Richmond’s Digital Scholarship Lab’s “Mapping Inequality” database
(Figure 2a, Richmond, VA, USA, [
29
]) to download each available city’s HOLC map shapefile
individually (n=239). To make analysis of Landsat-derived LST maps less computationally complex,
we then condense the 239 unique HOLC maps into a database of 108 US cities or urban areas that
overlap within Landsat 8 imagery tiles, and excluding any cities that were not mapped with at least
one of all four HOLC security rating categories (n=4). In some cases, HOLC map shapefile boundaries
needed to remove overlapping security rating boundaries, boundary crossings over bodies of water,
and to merge overlapping maps drawn in the same generalizable urban area and/or because they were
drawn during dierent years (Supplementary Materials I).
Climate 2020,8, 12 4 of 15
We assess patterns of intra-urban land surface temperatures in the 108 HOLC areas using
readily-accessible Landsat 8 satellite-derived northern hemisphere summertime (June–August) land
surface temperatures (LSTs) following accepted United States Geological Survey calculation protocol
(30
×
30 m resolution, TIRS Band 10, Normal Dierence Vegetation Index [NDVI] emissivity corrected
LST, Figure 2b [
20
,
30
,
31
]. This LST method relies on transforming raw Landsat 8 TIRS Band 10 data
into top-of-atmosphere spectral radiance and then into at-sensor brightness temperatures. LST is
then calculated by correcting the at-sensor brightness temperatures by surface emissivity calculated
from the NDVI (derived from Bands 4 and 5 [
30
]). LST maps were only generated from imagery that
satisfied a threshold for less than 10 percent scene cloud coverage and had to have been collected in the
northern hemisphere summertime between 2014 and 2017. While these LST descriptions of intra-urban
heat are coarse in spatial resolution and not the most representative of human-level, experiential
air temperatures which are better resolved by dense networks of air temperature and humidity
monitors [
13
,
32
], LST maps such as these have been widely applied to questions of large-scale patterns
related to urban land use and heat-related public health outcomes for individual US cities [20,33].
We then use Zonal Statistics in ESRI’s ArcGIS Spatial Analyst toolbox to estimate the mean of the
derived Landsat 8 LSTs within each individual HOLC security rating polygon within a given urban
area (e.g., Figure 2b,c). We then estimate each individual HOLC security rating polygon’s land surface
temperature anomaly from the area-wide mean LST from all HOLC security rating polygons (referred
to as δLST, Equation (1)).
δLSTarea,polygon =LSTarea,polygon LSTarea,all polygons (1)
This
δ
LST estimate gives us the ability to show relatively how much warmer or cooler a particular
HOLC security rating polygon is from the entire set of HOLC security rating polygons for a given
urban area, and then compare these anomalies between cities in a quantitative manner.
We also estimate average percent developed impervious surface land cover [
34
] and tree canopy
cover [
35
] within each HOLC polygon (Figure 2e,g) in each urban area as derived from the National
Land Cover Database (NLCD) 2011 [36]. NLCD tree canopy percent is a 30 m raster dataset covering
the coterminous United States, providing continuous percent tree canopy estimates derived from
multi-spectral Landsat imagery for each 30 m pixel. NLCD imperviousness reports the percentage
of urban developed surfaces that is impervious over every 30 m pixel in the coterminous United
States and beyond. These estimates of underlying land use and overlying tree canopy may not sum to
100 percent, as tree canopy can exist over all land use types within a HOLC polygon and not all land
use is necessarily impervious.
To compare
δ
LST variations within and among HOLC security ratings between cities, we then
average the estimated
δ
LST by HOLC security rating category within each city. This binning by HOLC
category yields how
δ
LST varies between HOLC security ratings within each city. We then binned
the
δ
LSTs for each city at the national scale (n=108) and by US Census Bureau regions: Northeast
(n=26),
South (n=29), Midwest (n=41), and Western (n=12). To estimate the significance of mean
temperature dierences between the HOLC security ratings by region and nationally, we apply a
post-hoc ANOVA multiple comparisons test known as Tukey’s Honest Significant Dierences (HSD)
Test. Tukey’s HSD test estimates dierences among group sample means for statistical significance.
This pairwise post-hoc ANOVA test determines the statistical significance of dierences between the
mean of all pairs of group means using a studentized range distribution.
Climate 2020,8, 12 5 of 15
Climate 2020, 8, x FOR PEER REVIEW 5 of 15
Figure 2. Demonstration of HOLC Security Grade δLST and land cover analysis for Richmond, VA
(grey outline). (a) HOLC Polygons for Richmond, VA [29] (see Introduction text for explanations of
HOLC security grade color designations), (b) LST map for Richmond, VA derived from Landsat 8
TIRS Band 10 imagery collected on 2 July 2016, and (c) Resulting δLSTs in HOLC polygons calculated
as the anomaly of an individual HOLC polygon to the city-wide HOLC polygon average LST (see
Equation (1)), (d) box–whisker plot of the δLSTs presented in (c) binned by HOLC security rating (see
Introduction text for explanations of designations), (e) percent tree canopy from NLCD 2011 [36]
averaged into HOLC polygons, (f) box–whisker plot of the δLSTs presented in (e) binned by HOLC
security rating, (g) percent developed impervious surface from NLCD 2011 [36] averaged into HOLC
polygons, (h) box–whisker plot of the average imperviousness presented in (g) binned by HOLC
security rating.
3. Results
Our LST maps were generated from Landsat 8 acquisitions that satisfied a < 10 percent scene
cloud coverage threshold collected from 3 June 2014 to 25 August 2017 (Supplementary Materials
Table S1). These mostly sunny days provide the best conditions for Landsat 8 to reliably capture a
strong LST pattern in urban areas [32]. Approximately 40 percent of the Landsat 8 imagery was
collected during the 2016 northern hemisphere summer, while ~10 percent of the imagery was
collected during the 2014 northern hemisphere summer. Regression tests reveal an insignificant
Figure 2.
Demonstration of HOLC Security Grade
δ
LST and land cover analysis for Richmond, VA
(grey outline). (
a
) HOLC Polygons for Richmond, VA [
29
] (see Introduction text for explanations of
HOLC security grade color designations), (
b
) LST map for Richmond, VA derived from Landsat 8
TIRS Band 10 imagery collected on 2 July 2016, and (
c
) Resulting
δ
LSTs in HOLC polygons calculated
as the anomaly of an individual HOLC polygon to the city-wide HOLC polygon average LST (see
Equation (1)), (
d
) box–whisker plot of the
δ
LSTs presented in (
c
) binned by HOLC security rating
(see Introduction text for explanations of designations), (
e
) percent tree canopy from NLCD 2011 [
36
]
averaged into HOLC polygons, (
f
) box–whisker plot of the
δ
LSTs presented in (
e
) binned by HOLC
security rating, (g) percent developed impervious surface from NLCD 2011 [36] averaged into HOLC
polygons, (
h
) box–whisker plot of the average imperviousness presented in (
g
) binned by HOLC
security rating.
3. Results
Our LST maps were generated from Landsat 8 acquisitions that satisfied a <10 percent scene
cloud coverage threshold collected from 3 June 2014 to 25 August 2017 (Supplementary Materials Table
S1). These mostly sunny days provide the best conditions for Landsat 8 to reliably capture a strong LST
pattern in urban areas [
32
]. Approximately 40 percent of the Landsat 8 imagery was collected during
the 2016 northern hemisphere summer, while ~10 percent of the imagery was collected during the 2014
Climate 2020,8, 12 6 of 15
northern hemisphere summer. Regression tests reveal an insignificant relationship between the day
that the imagery was collected and the resulting δLST patterns (Supplementary Materials Table S1).
Our analysis reveals three major trends that help to address our research questions. First, LST
dierences across the cities follow a non-uniform distribution of dierences, suggesting that historical
redlining policies are reflected in present-day intra-urban heat dierentially (Supplementary Materials
Table S1). Notable, intra-city
δ
LST dierences between areas given “D” and “A” HOLC security ratings
range between +7.1
C (Portland, OR) to
1.5
C (Joliet, IL, USA), with ~94% of urban areas included
in this study showing warmer present-day LSTs in their “D”-rated areas relative to their “A”-rated
areas (Supplementary Materials Table S1). While Portland (OR) and Denver (CO) had the greatest “D”
to “A” security rating dierences within a city, the warmest
δ
LST temperatures in formerly redlined
areas relative to the city-wide average LST were identified in Chattanooga (TN, 3.3
C) and Baltimore
(MD, 3.2
C). These cities were in contrast to formerly redlined areas that displayed, on average, cooler
surface temperatures than their non-redlined counterparts (e.g., Joliet, IL, USA and Lima, OH, USA), a
consistent pattern in several cities across the Midwest (Supplementary Materials Table S1). Patterns
of relatively pronounced or muted
δ
LST are underscored by attendant patterns of land use type and
cover within the same HOLC security rating polygons, whereby the urban areas with the highest D-A
dierence and largest
δ
LST in D-rated polygons show considerable HOLC rating-specific trends in
average tree canopy and developed impervious surface percentages as compared to the Midwestern
cities that exhibit cooler-than-average
δ
LST patterns in their D-rated areas (Supplementary Materials
Figure S1). The coolest
δ
LST temperatures in areas assigned “A” HOLC security ratings relative to the
city-wide average LST were identified in Birmingham (AL, 4.7 C) and Roanoke (VA, 4.5 C).
Regional aggregation of the city-specific trends reveals that average
δ
LST dierences between
HOLC security rating categories exhibit a pattern of incremental warming relative to worsening HOLC
security rating (Figure 3b–e). However, the magnitude of the
δ
LST dierences varies considerably by
region, with the Midwest (n=41) showing more muted
δ
LST dierences than the Southeast (n=29)
and West (n=12), respectively (Figure 3b–e). Honest Significant Dierence tests on urban areas at
the regional scale reveal that the greatest
δ
LST dierences exist between “A” and “D” HOLC security
rating areas across US regions, with “D”-rated areas progressively warmer than each subsequent rating
in the present day. These amplified dierences in the West and Southeast, as well as the relatively
muted response in the Midwest (Figure 3b–e), are attended by similar dierences in underlying percent
land use cover (Figure 4b–e), and especially apparent in the available tree canopy (Figure 5b–e) for the
areas assigned “A” HOLC security ratings.
A third trend that is consistent in a national-scale aggregation of
δ
LSTs in these cities is the finding
that “D”-rated areas are now on average 2.6
C warmer than “A”-rated areas (Figure 3a). Each HOLC
security rating category warms systematically relative to the more favorable neighbor security rating
category (Figure 3a). Honest Significant Dierence tests reveal that areas given “D” HOLC security
ratings are significantly warmer than all of the other HOLC security rating categories at the national
scale, in progressively larger magnitudes. These LST dierences are underscored by similar, but
opposing, national-scale patterns in underlying land use and tree canopy within the same redlined
cities (Figures 4a and 5a), showing that areas assigned a “hazardous” HOLC security rating in US cities
exhibit quantitatively less coverage by tree canopy and more coverage by impervious surfaces in the
present decade [35,36].
Climate 2020,8, 12 7 of 15
Figure 3.
(
a
) National-scale Land Surface Temperature Anomalies by HOLC security rating (Green,
“Best,” A; Blue, “Still Desirable,” B; Yellow, “Definitely Declining,” C; Red, “Hazardous,” D) (
b
) same
as (
a
)
,
but for the Midwest region; (
c
) same as (
b
), but for Northeast region; (
d
) same as (
b
), but for
West region; (e) same as (b), but for South region.
Climate 2020,8, 12 8 of 15
Climate 2020, 8, x FOR PEER REVIEW 8 of 15
Figure 4. (a) National-scale averages of underlying percent developed impervious surface [36] by
HOLC security rating (Green, “Best,” A; Blue, “Still Desirable,” B; Yellow, “Definitely Declining,” C;
Red, “Hazardous,” D), (b) same as (a), but for the Midwest region; (c) same as (b), but for Northeast
region; (d) same as (b), but for West region; (e) same as (b), but for South region.
Figure 4.
(
a
) National-scale averages of underlying percent developed impervious surface [
36
] by
HOLC security rating (Green, “Best,” A; Blue, “Still Desirable,” B; Yellow, “Definitely Declining,” C;
Red, “Hazardous,” D), (
b
) same as (
a
), but for the Midwest region; (
c
) same as (
b
), but for Northeast
region; (d) same as (b), but for West region; (e) same as (b), but for South region.
Climate 2020,8, 12 9 of 15
Climate 2020, 8, x FOR PEER REVIEW 9 of 15
Figure 5. (a) National-scale averages of percent tree canopy [35,36] by HOLC security rating (Green,
“Best,” A; Blue, “Still Desirable,” B; Yellow, “Definitely Declining,” C; Red, “Hazardous,” D), (b) same
as (a), but for the Midwest region; (c) same as (b), but for Northeast region; (d) same as (b), but for
West region; (e) same as (b), but for South region.
4. Discussion and Conclusions
We sought to understand the extent to which historic policies of redlining help to explain current
patterns of intra-urban heat and the extent to which these patterns were consistent across US cities.
Questions about the increasing economic inequality in US society motivated our inquiry and suggest
several patterns related to historical federal housing policies and which communities experience the
hottest areas of a city in the present day. Most notably, the consistency of greater temperature in
formerly redlined areas across the vast majority (94%) of the cities included in this study indicates
that current maps of intra-urban heat echo the legacy of past planning policies. While earlier studies
document the lack of present-day services for and lower income of communities living in formerly
redlined areas, this analysis presents an argument for understanding how global climate change will
further exacerbate existing, historically-codified inequities in the US. We highlight three important
dimensions of our findings—built environment, policies, and current inequities—as they relate to
implications of these results.
First, our findings corroborate earlier studies that describe consistent patterns between the lack
of tree canopy and historically underserved urban areas, at the national and regional scales (Figures
4 and 5). The prevalence of impervious surfaces as opposed to tree canopy points to the fact that
green spaces have been consistently more abundant in wealthier and majority White-identifying
Figure 5.
(
a
) National-scale averages of percent tree canopy [
35
,
36
] by HOLC security rating (Green,
“Best,” A; Blue, “Still Desirable,” B; Yellow, “Definitely Declining,” C; Red, “Hazardous,” D), (
b
) same
as (
a
), but for the Midwest region; (
c
) same as (
b
), but for Northeast region; (
d
) same as (
b
), but for
West region; (e) same as (b), but for South region.
4. Discussion and Conclusions
We sought to understand the extent to which historic policies of redlining help to explain current
patterns of intra-urban heat and the extent to which these patterns were consistent across US cities.
Questions about the increasing economic inequality in US society motivated our inquiry and suggest
several patterns related to historical federal housing policies and which communities experience the
hottest areas of a city in the present day. Most notably, the consistency of greater temperature in
formerly redlined areas across the vast majority (94%) of the cities included in this study indicates
that current maps of intra-urban heat echo the legacy of past planning policies. While earlier studies
document the lack of present-day services for and lower income of communities living in formerly
redlined areas, this analysis presents an argument for understanding how global climate change will
further exacerbate existing, historically-codified inequities in the US. We highlight three important
Climate 2020,8, 12 10 of 15
dimensions of our findings—built environment, policies, and current inequities—as they relate to
implications of these results.
First, our findings corroborate earlier studies that describe consistent patterns between the lack of
tree canopy and historically underserved urban areas, at the national and regional scales (Figures 4
and 5). The prevalence of impervious surfaces as opposed to tree canopy points to the fact that
green spaces have been consistently more abundant in wealthier and majority White-identifying
neighborhoods [
26
]. At the same time, intra-urban heat is not only aected by tree cover, since the use
of dierent materials within varying urban typologies also amplifies temperatures [
19
,
37
]. Two features
of the urban landscape—roadways and large building complexes—are well known to transform solar
radiation into heat. These landscape features absorb the energy-filled short-wave radiation coming
from the sun, and re-emit long-wave radiation during the diurnal heating-cooling process. As a
result, large roadways and building complexes gain heat during the day and, as the evening cools
ambient temperatures, the retained heat is released back into the neighborhoods, which is captured by
overhead satellite sensors. These evening temperatures are precisely the factors that can exacerbate
excess mortality and morbidity [38].
An earlier body of evidence from the regional studies and economics literature makes the
connection between federal programs that provided incentives for major roadway and building
construction projects and the fact that many of these occurred in the lowest income neighborhoods
of cities [
39
41
]. In fact, the 1950s were an important decade for the creation of major roadways
across the US, and many redlined neighborhoods were transformed and divided by road and highway
infrastructure projects [
42
]. These changes came at a time when intra-urban heat was not recognized
as a major public health hazard, and yet, given the well-known heat-absorbing capacity of asphalt and
concrete [43], the selection of these materials may underlie the dierences revealed in these results.
Similarly, throughout the mid-1900s large building complexes, including housing complexes,
industries, and university campuses, often subsidized by the federal government, were also placed in
redlined areas, largely due to the inexpensive land, and current population of largely lower income and
communities of color [
44
]. From the 1940s through the 1970s, large buildings were made of high-density
materials, such as cinder block and brick, which retain heat, and maintain high temperatures through
the night [
45
,
46
]. Many of these buildings still stand, and the LST maps investigated here partially
describe the thermal signature of these buildings. Areas that were in non-redlined areas, often built
of other materials but also dispersed across a more natural, maintained landscape, which allows for
greater circulation of air [47,48] are hence the cooler neighborhoods registered by satellites.
Second, dierences in implementing policies and landscapes may help to explain the variation
of temperatures across dierent regions of the US. The cities of Portland (OR), Denver (CO), and
Minneapolis (MN), for example, notably reflect the largest dierences between the formerly redlined
areas and their non-redlined counterparts (Supplementary Materials Table S1). We can speculate that
the redlined areas of all three cities are currently located in areas with extensive physical infrastructure,
including housing complexes, railway terminals, industrial or manufacturing sites, and/or adjacent
to major business centers. The presence of these current day land uses may suggest a relationship
between formerly inexpensive land and large-scale development. These results, when combined
with more pernicious modern-day policies that support development of high-asphalt and low tree
canopy areas such as massive shopping complexes that contain large surface parking lots, are further
strengthened. In Portland (OR), for example, decades of development code allowed for multifamily
complexes to cover 100% of the lot area with no provisions for greening. Only recently, and due to
extensive support from local researchers and community organizations did the city evaluate earlier
asphalt-driving policy to require 85% lot coverage and green spaces [
49
,
50
]. Such reversals of policy
are the forms of planning that can help to reverse decades of amplifying temperatures in areas that
have historically been underserved. Denver and Minneapolis are also making strides, though without
further understanding about the historic and present-day drivers that generate these asphalt-rich and
tree canopy-poor land uses on intra-urban heat, and local communities, progress will be slow.
Climate 2020,8, 12 11 of 15
In addition, the coupling of landscape and historic designs of urban development in these cities
may also play a role in helping to explain dierences across the country. Portland, like Minneapolis,
are in landscapes where tree canopy is relatively easy to sustain. Unlike arid and drought-prone areas,
where planting trees can require extensive maintenance, the warm, sunny summers and wet/snowy
winters of Portland, Minneapolis and other cities of the Northwest and Midwest, provide ideal
conditions for expanding an urban forest, which can, in turn, reduce surface temperatures of a
neighborhood. Tree planting eorts often took place as part of urban development projects in the early
and mid-1900s, and were used as a way to mark special designations [
42
]. Similarly, metropolitan
areas that conform to the concentric zone model (for example, places like Chicago, Los Angeles, and
Philadelphia) tend to be larger and more densely populated metros, often with a higher degree of both
auence and inequality, a larger African American population, and a greater share of population in
the suburbs. In the remaining metropolitan areas, there is greater integration between the auent and
the poor [
44
]. In these places, such as Seattle (WA), Charleston (WV), and Birmingham (AL), the rich
are concentrated in the urban core, where redlining and tree planting eorts coincide.
Finally, indicators of and/or higher intra-urban LSTs have been shown to correlate with higher
summertime energy use [
51
,
52
], and excess mortality and morbidity [
20
,
53
,
54
]. The fact that residents
living in formerly redlined areas may face higher financial burdens due to higher energy and more
frequent health bills further exacerbates the long-term and historical inequities of present and future
climate change. As the results from earlier studies have documented income inequality between
formerly redlined areas another other parts of US cities, we recognize that hotter areas will amplify
these current inequities. Such historic income inequality leads to income segregation because higher
incomes, which are further supported by past and current housing policy, allow certain households
to sort themselves according to their preferences—and control local political processes that continue
exclusion [
55
]. Other explanatory factors of these patterns, though too many for the current study and
setting the stage for future studies, include disinvestment in urban areas, suburban investment and
land use patterns, and the practices generally of government and the underwriting industry [39,56].
To our knowledge, this is the first study to link a historical federal housing policy to the creation
(or at least the exacerbation) of a climate stressor and potential variability in resident exposure to it.
While redlining most likely did not create the microenvironments that mediate LSTs relative to the rest
of the urban environment, our findings suggest a strong and significant likelihood of the cauterization
of current day exposure to the hottest parts of a city. While patterns of who experiences the most
exposure to intra-urban heat may change as a result of (green) gentrification, which many formerly
redlined neighborhoods are undergoing (e.g., wealthier communities can aord to green and change
the physical landscape, and, over time, cool the hottest areas of a city), we observe consistent patterns
that can be inferred as in part due to the creation of HOLC maps [
23
]. Future studies will need to
describe the mechanisms by with planning practices—past and present—are likely to amplify the
eects of climate change on historically underserved communities and communities of color.
While a growing body of evidence describes the intra-urban variation of temperatures
due to characteristics of the built environment, few have asked why we observe a pattern of
historically-marginalized communities living in the hottest areas. Here we have presented results from
an analysis of 108 US cities that aimed to examine the role of historic “redlining” policies in mediating
exposure to intra-urban heat. We found that in nearly all cases, those neighborhoods located in formerly
redlined areas—that remain predominantly lower income and communities of color—are at present
hotter than their non-redlined counterparts. Although the extent of dierences in temperatures varies
by region, the preponderance of evidence establishes that those experiencing the greatest exposure
to present and potentially future extreme heat are living in neighborhoods with the least social and
ecosystem services historically.
As more and more communities race to develop plans to react to and adapt to worsening
extreme heat and its attendant eects on human health [
57
], a research agenda focused on developing
place-specific, heat-mitigating urban designs and interventions [
58
61
] will be critical toward not
Climate 2020,8, 12 12 of 15
only alleviating heat disparity but ensuring that the urban forms and policies that gave rise to these
inequities in our past (like redlining) are recognized and altogether avoided. Furthermore, crafting
climate equity-centered policies that recognize decades of disproportionate exposure to environmental
stressors can help any new discoveries in urban design get implemented with focus and rapidity.
Supplementary Materials:
The following are available online at http://www.mdpi.com/2225-1154/8/1/12/s1,
Figure S1: Comparison of urban areas of relatively large or small dierences in LSTs between HOLC grades,
Table S1: Urban area-specific results from our LST analysis.
Author Contributions:
J.S.H. conceived the project and coordinated the analysis, advised interpretation, and
contributed to the manuscript, created figures, and coordinated the responses to reviewers. V.S. provided major
contributions to the manuscript including context, interpretation, editorialization, and literature review and
references. N.P. performed HOLC map and satellite imagery download and spatial analyses. All authors have
read and agreed to the published version of the manuscript.
Funding: This research involved no external funding.
Acknowledgments:
J.S.H. thanks the NOAA Oce of Education Environmental Literacy Program, the Virginia
Academy of Science, Groundwork RVA, Virginia Commonwealth University SustainLab, University of Richmond
Spatial Analysis and Digital Scholarship Labs, and the City of Richmond Sustainability Oce. J.S.H. and V.S.
acknowledge support from the NOAA Climate Program Oce, and U.S. Forest Service’s National Urban and
Community Forestry Challenge Grants Program (No. 17-DG-11132544-014). N.P. acknowledges the work study
program at the Virginia Commonwealth University. The authors thank four anonymous reviewers for their
thoughtful and thorough consideration.
Conflicts of Interest: The authors declare no conflict of interest.
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... Black Americans are 52% more likely than average to live in areas where a high risk for heat-related health problems exists, while Latino/a communities are 21% more likely to live under such conditions (Jesdale et al., 2013). Residents of neighborhoods that were formerly subject to "redlining"-a Federal practice that determined home lending risk based on racial composition-experience surface temperatures that are on average 2.6 • C (4.7 • F) and up to 7 • C (12.6 • F) hotter compared to their non-redlined counterparts in the same city, even more than 50 years after the end of this redlining policy; these higher temperatures are correlated with lower UTC (Hoffman et al., 2020). During extended heat waves in LA, mortality increases about five-fold from the first to the fifth consecutive day; after the fifth day, mortality risk increases 46% in Latino/a communities and 48% in elderly Black communities (Kalkstein et al., 2014). ...
... More than half a century after the end of redlining, the legacy patterns of disinvestment are still evident today, and they are evident in our findings (Table 1, Figures 8,9). A spatial assessment of 108 urban areas in the US, including Los Angeles, found that in addition to being hotter, in 94% of cases formerly redlined neighborhoods presently have two to three times less tree cover than their wealthier, non-redlined counterparts (Hoffman et al., 2020). Our study indicates that raising awareness of these enduring legacies of injustice can be a motivating factor for engaging in their undoing, and that tree stewardship can serve as a tangible act of addressing the causes of injustice. ...
Article
Full-text available
Extreme heat in the United States is a leading cause of weather-related deaths, disproportionately affecting low-income communities of color who tend to live in substandard housing with limited indoor cooling and fewer trees. Trees in cities have been documented to improve public health in many ways and provide climate regulating ecosystem services via shading, absorbing, and transpiring heat, measurably reducing heat-related illnesses and deaths. Advancing “urban forest equity” by planting trees in marginalized neighborhoods is acknowledged as a climate health equity strategy. But information is lacking about the efficacy of tree planting programs in advancing urban forest equity and public wellbeing. There is a need for frameworks to address the mismatch between policy goals, governance, resources, and community desires on how to green marginalized neighborhoods for public health improvement—especially in water-scarce environments. Prior studies have used environmental management-based approaches to evaluate planting programs, but few have focused on equity and health outcomes. We adapted a theory-based, multi-dimensional socio-ecological systems (SES) framework regularly used in the public health field to evaluate the Tree Ambassador, or Promotor Forestal , program in Los Angeles, US. The program is modeled after the community health worker model—where frontline health workers are trusted community members. It aims to address urban forest equity and wellbeing by training, supporting, and compensating residents to organize their communities. We use focus groups, surveys, and ethnographic methods to develop our SES model of community-based tree stewardship. The model elucidates how interacting dimensions—from individual to society level—drive urban forest equity and related public health outcomes. We then present an alternative framework, adding temporal and spatial factors to these dimensions. Evaluation results and our SES model highlight drivers aiding or hindering program trainees in organizing communities, including access to properties, perceptions about irrigation responsibilities, and lack of trust in local government. We also find that as trainee experience increases, measures including self- and collective efficacy and trust in their neighbors increase. Findings can inform urban forestry policy, planning, and management actions at the government and non-profit levels that aim to increase tree cover and reduce heat exposure in marginalized communities.
... For example, Hoffman et al. found that 94% of 108 cities studied showed patterns of elevated land surface temperatures in D-graded areas compared to A-graded areas, but in some cities in the Midwest, the pattern was reversed. Further, the intra-city difference in land surface temperature anomaly from the citywide mean, between D-as compared to A-graded areas, ranged from + 7.1 to − 1.5 °C [48]. In another study examining multiple health outcomes across nine cities, in St. Louis, there was little evidence of an association with redlining, while in five cities, the majority of outcomes exhibited a statistically significant association, including for outcomes for which a significant relationship was not observed in the overall sample [33]. ...
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Following the Great Depression and related home foreclosures, the federal government established new agencies to facilitate access to affordable home mortgages, including the Home Owners' Loan Corporation (HOLC) and Federal Housing Administration (FHA). HOLC and FHA directed widespread neighborhood appraisals to determine investment risk, referred to as "redlining," which took into account residents' race. Redlining thereby contributed to segregation, disinvestment, and racial inequities in opportunities for homeownership and wealth accumulation. Recent research examines associations between historical redlining and subsequent environmental determinants of health and health-related outcomes. In this scoping review, we assess the extent of the current body of evidence, the range of outcomes studied, and key study characteristics, examining the direction and strength of the relationship between redlining, neighborhood environments, and health as well as different methodological approaches. Overall, studies nearly universally report evidence of an association between redlining and health-relevant outcomes, although heterogeneity in study design precludes direct comparison of results. We critically consider evidence regarding HOLC's causality and offer a conceptual framework for the relationship between redlining and present-day health. Finally, we point to key directions for future research to improve and broaden understanding of redlining's enduring impact and translate findings into public health and planning practice.
... 22 This study adds yet another example of pervasive racial and ethnic disparities in the United States-such as that of redlining leading to outcomes of reduced access to greenspace 32 or increased exposure to extreme heat. 33 Since the time of the study, 5 CFPPs have closed and 3 more plan to close in coming years. The most recent projected closure of the Columbia Power Plant by 2025 was announced in February 2021. ...
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Background: Burning fossil fuels, including coal, is the primary source of greenhouse gas emissions driving anthropogenic climate change and its associated health harms. Coal-fired power plants supply 23% of electricity nationally and 42% for Wisconsin, contributing to air pollution and associated respiratory diseases, cancers, and cardiovascular and neurologic disorders, especially for vulnerable populations. Authors seek to quantify residential distance from coal-fired power plants, pulmonary function of Wisconsin residents, and demographics. Methods: Data from 2,327 adults aged 21-74 years was obtained from the Survey of the Health of Wisconsin database from 2008 through 2013. Pulmonary function was measured by expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) as a ratio of FEV1/FVC. An average of at least 3 FEV1/FVC readings less than 80% was considered abnormal. Results: Adults living near 1 of 11 coal-fired power plants may have worse pulmonary function. The odds ratio of FEV1/FVC values below 80% for those living within 35 km of a coal-fired power plant was 1.24 (95% CI, 0.90-1.70) when compared to those living greater than 35 km from a plant. While Black individuals made up 4.8% of the total sample population, they accounted for 13.3% of individuals living within 35 km of coal-fired power plants. Similarly, Hispanic populations accounted for 4.8% of those living within 35 km of a plant, while making up 2.8% of the sample population. Interpretation: Significant disparities were found in residential proximity to Wisconsin coal-fired power plants for Black and Hispanic populations, with trends that support worse pulmonary function when living within 35 km of these plants. When linked with socioeconomic and racial/ethnic factors, closing down coal-fired power plants becomes a necessity to reduce disparities and address environmental injustices.
... The practice of grading neighborhoods was imbued with racism and xenophobia and led to financial disinvestment and resource deficiencies in communities where Black, indigenous, people of color (BIPOC) resided and currently reside (Nardone et al. 2020;Nelson et al. 2020). The legacies of historic redlining include hotter temperatures (Hoffman et al. 2020;Wilson 2020), reduced tree canopy (Locke et al. 2021) and green space (Nardone et al. 2021), more gun violence (Benns et al. 2020) and more alcohol sales outlets (Lee et al. 2020). Areas of Pittsburgh that were graded unfavorably (red or yellow) by the HOLC were shown in recent decades to have a larger proportion of African American residents, a higher concentration of poverty, higher rates of population loss, and a lower rate of homeownership (Rutan and Glass 2018). ...
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In the 1930s, the Home Owners’ Loan Corporation (HOLC) graded the mortgage security of urban US neighborhoods. In doing so, the HOLC engaged in the practice, imbued with racism and xenophobia, of “redlining” neighborhoods deemed “hazardous” for lenders. Redlining has caused persistent social, political and economic problems for communities of color. Linkages between redlining and contemporary food access remain unexamined, even though food access is essential to well-being. To investigate this, we used a census tract-level measure of low-income and low grocery store food access from the US Department of Agriculture Food Access Research Atlas, redlining data from Mapping Inequality Project, and demographic data from the American Community Survey. We employed generalized estimating equations with robust covariance estimates to analyze data pertaining to 10,459 census tracts in 202 US cities. Tracts that the HOLC graded as “C” (“decline in desirability”) and “D” (“hazardous”) had reduced contemporary food access compared to those graded “A” (“best”). Increases in contemporary census tract proportions of Black, Hispanic, or other racial/ethnic minority residents, as well as disabled residents, were associated with reduced food access. Increases in contemporary proportions of residents age 75 years and older or those without a car were associated with better food access. Tracts that underwent housing redevelopment since being graded had better food access, while those undergoing gentrification had reduced food access. Results suggest that issues of redlining, housing discrimination, racism, ableism, displacement, and food inaccessibility are deeply intertwined.
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Redlining was a practice of financial discrimination in the mid-20th century in which banks refused loans or increased interest rates based on the grade of an applicant’s neighborhood as designated by the federally sponsored Home Owner’s Lending Commission (HOLC). The HOLC primarily graded neighborhoods from “A” (best) to “D” (hazardous) based on characteristics including the racial demographics and economic status of the residents, with neighborhoods with higher percentages of non-white and/or recent immigrant residents given lower grades; this and similar discriminatory practices can be traced to modern-day economic and environmental inequalities between neighborhoods. The legacy of redlining and related housing discrimination on modern-day urban air quality, which presents a significant threat to public health, remains an important issue in addressing environmental injustice in U.S. cities. In our study, we used remotely sensed estimates of the air pollutant nitrogen dioxide (NO2) collected with the TROPOMI satellite sensor, and shapefiles of redlined neighborhoods, to determine whether air quality varies among historic HOLC grades in 11 U.S. Midwestern metropolitan areas. This approach allowed us to test these tools for within-city analysis of NO2 for which high spatial and temporal resolution measurements are not often available, despite their importance for monitoring impacts on human health. We found that NO2 levels were as much as 16% higher in neighborhoods that were graded “D” compared to those graded “A” (as in Chicago), with the mean difference across all cities an increase of 7.3% ± 5.9%. These results present evidence of persistent modern-day inequality in urban air quality associated with historic discriminatory policies and should be used as an argument for government action improving air quality in neighborhoods that were poorly graded by the HOLC.
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This study uses a boundary design and propensity score methods to study the effects of the 1930s-era Home Owners Loan Corporation (HOLC) “redlining” maps on the long-run trajectories of urban neighborhoods. The maps led to reduced home ownership rates, house values, and rents and increased racial segregation in later decades. A comparison on either side of a city-level population cutoff that determined whether maps were drawn finds broadly similar conclusions. These results suggest the HOLC maps had meaningful and lasting effects on the development of urban neighborhoods through reduced credit access and subsequent disinvestment. (JEL G21, J15, N32, N42, N92, R23, R31)
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