Planning for Heat Vulnerability
A Proposed Methodology for Evaluating 20th Century Local Planning Policy Influence on 21st Century Urban Heat Vulnerability
The urban form of cities across the United States is currently hindering their ability to adapt to extreme climate events. In climate change discussions, the field of urban planning is often framed as a pathway forward to city adaptability and vulnerability reduction (IPCC, 2014). However, before planners use their regulatory land use tools and strategies to plan for the climate crisis, there must be understanding and reflection on how those same tools and policies have contributed to current climate concerns in cities, namely the Urban Heat Island Effect. As we progress into a new era of climate change, cities must understand the history and rationality behind their urban growth and development and recognize opportunities to strengthen urban regions' adaptive capacities.
Introduction
The urban form of cities across the United States is currently hindering their ability to adapt to extreme climate events. In climate change discussions, the field of urban planning is often framed as a pathway forward to city adaptability and vulnerability reduction (IPCC, 2014). However, before planners use their regulatory land use tools and strategies to plan for the climate crisis, there must be understanding and reflection on how those same tools and policies have contributed to current climate concerns in cities, namely the Urban Heat Island Effect.
As we progress into a new era of climate change, cities must understand the history and rationality behind their urban growth and development and recognize opportunities to strengthen urban regions' adaptive capacities.
The following proposed research is two-fold. Researchers including Hoffman et al. (2020) and Wilson (2020) have established a method using Federal Home Owner’s Loan Corporation (HOLC) historical mortgage lending maps (“redlining” maps) to link planning policies to existing adaptive capacity and heat exposure. In the first part of this research, I will attempt to triangulate a similar method without the use of these HOLC maps through the use of ArcGIS software, available city and neighborhood plans between 1907 - 2000, as well as historical census data. Secondly, I will test this method by using it to explore the long-term impacts that 20th-century urban planning policies have had on residential and neighborhood heat vulnerability and identify if particular communities, including racial minorities, were disproportionately and negatively affected by these policies.
Photos: Aerial Imagery of Cincinnati showing the changes to urban form. Left: 1955, Right: 2013 ( Source )
Urban Heat Islands
Urban Heat Islands describe the phenomenon of the ambient air and surface temperatures within cities being several degrees higher than surrounding rural areas (Huang, Zhou, & Cadenasso, 2011). Current literature centered around UHI has found that surface temperatures are increasing during the daytime, and that there is also a lack of cooling during afternoons and evenings (Dixon & Mote, 2003). As both the urbanization of cities and their populations increase, so does the difference in temperature between cities and their rural counterparts, resulting in the Urban Heat Island Effect (Kleerekoper, van Esch, & Salcedo, 2012).
Additionally, the land surface temperatures and overall climate within the city itself are shown to differ at higher rates depending on each neighborhood's physical qualities, forming varying microclimates (Kleerekoper, van Esch, & Salcedo, 2012). Land surface temperature is determined by the urbanization of the physical landscape and the area’s vegetation density (Mitchell & Chakraborty, 2015). Microclimates in neighborhoods with few trees and high amounts of impervious surfaces see more extreme temperatures than other well-shaded areas (Sherman, 2020)
Right: Comparing Land Cover (NLDC, 2016) to Average Surface Temperature (Source: Groundwork Ohio River Valley )
Heat Vulnerability
As extreme weather-related events continue to increase in frequency and duration, there will be an irregular distribution and amplification of risk across cities (IPCC, 2014). As cities continue to grow hotter, the Urban Heat Island Effect will amplify the disparate effects on residents facing high heat vulnerability (IPCC, 2014). Heat vulnerability can be understood by reviewing the following factors and their relationship to extreme heat: Exposure, Sensitivity, and Adaptive Capacity (Voelkel, Hellman, Sakuma, & Shandas, 2017).
Right: Heat Vulnerability Index in Cincinnati by Census Block Group. (Data Source: Groundwork Ohio River Valley )
UHIs & Urban Planning
At the start of the 20th century, urban residents in the United States were first beginning to outnumber their rural counterparts (Platt, 2014). Urban planning, a profession growing within the United States at that same time, was a primary shaper of the physical environment of cities (Wilson, 2020).
The profession began in the United States, hoping to enhance housing and sanitization in modern settings as the cities grew (Platt, 2014) through regulatory land-use decisions, including zoning (Northridge & Freeman, 2011). These land-use techniques are responsible for the location of structures and spaces, such as highways, parks, and residential neighborhoods.
Right: Cincinnati's 1925 Regional Plan Map. Source: Historical Information on Greater Cincinnati
20th century city planning policies and practices contributed to the inequitable growth of suburban sprawl (Platt, 2014), a concept previously noted as responsible for amplifying the UHI effect in cities throughout the United States.
In the century following the 1926 legal establishment of zoning regulations, urban planning policies have shaped cities' built environments, favoring automobile-centric developments of single-family homes outside of urban centers following World War II (Platt, 2014). Profoundly racist undertones accompanied the 20th-century land use tools and policies that led to both “white flight” (Platt, 2014) and suburban sprawl. Recurring policies and strategies discussed in the literature include the practices of redlining, federal and state tax policies, the federal Interstate Highway System, and local zoning codes (Platt, 2014).
Right: The Downtown Motorways Plan from Cincinnati's 1948 Master Plan. ( Source )
Existing Research
A significant breakthrough in documenting the connection between urban planning policies and environmental injustice has arisen in recent research surrounding the Home Owners Loan Corporation (HOLC) and its associated redlining policy. This New Deal-era federal policy ostensibly supported federally-backed mortgage loans (Platt, 2014). This process involved local HOLC agents and appraisers categorizing neigborhoods within cities across the United States with populations over 40,000 based on mortgage risk (Nelson, 2020). Neighborhoods were judged by HOLC agents on whether or not they were safe investments for mortgage lenders with a grading scale of “A”, for neighborhoods determined to be safe investments, down to “D” for neighborhoods described as “Hazardous” (Nelson, 2020). These ratings also had a corresponding scale of colors on the official maps, with “A” rated neighborhoods shaded with green, and “D” neighborhoods shaded in red, resulting in the practice being referred to as “Redlining” (Aaronson, Hartley, & Mazumder, 2020).
Prominent research from Hoffman et al. (2020) found that out of the 108 cities included in this study, 94% were determined to have a significant relationship between HOLC planning policies and current land surface temperatures, with cooling elements such as greenspaces and high tree canopy coverage located in wealthier, white neighborhoods. Additionally, researchers found a significant difference in surface temperatures between A (“Best”) and D (“Hazardous”) security ratings (Hoffman, Shandas, & Pendleton, 2020), with D rated areas seeing consistently warmer temperatures than the neighborhoods that received higher ratings. These findings connected the current environmental hazards to the historic development strategy.
(Above) An additional analysis completed by GroundworkUSA, analyzing factors of Heat Vulnerability in comparison to the Richmond HOLC Map. (Source: Groundwork USA's Climate Safe Neighborhoods Program )
Researchers and advocates have seen success in using the HOLC Redlining maps to investigate past planning policies' damage, establishing the need for intentional investment in climate-focused resiliency projects and programs grounded in environmental justice.
By evaluating the HOLC Redlining maps of the early to mid 20th century, communities and researchers have been able to contextualize the historic policies that have contributed to inter-urban heat islands. While this research is beneficial for the environmental justice community and conversation, cities that do not have an official HOLC redlining map are disadvantaged. Additionally, by centering research and conversations solely around historic redlining maps and associated systems, these conversations leave out the other harmful urban planning policies and tools from the 20th century that have shaped modern cities.
Right: The closest thing to a "Redlining" Map of Cincinnati. (Source: Ohio State University Libraries )
About The Research
This research proposes an evaluation method of these city policies through a spatial analysis of digitized comprehensive and neighborhood plans from between 1907 and 1980 to understand the impact that they each have had on modern neighborhood heat vulnerability. Elements identified to have influenced risk of inter-Urban Heat Islands will be quantified and evaluated based on the proposed changes to urban form to determine if the changes contributed to the risk of modern intra-urban heat islands.
A secondary statistical analysis will test to see if there is a relationship between each plan’s contribution to inter-urban heat island risk (identified in the initial analysis) and historic racial demographic data from the corresponding year. The results of these two analyses will determine if the following hypothesis is correct: Neighborhoods with current higher heat vulnerability rates received more UHI-enabling developments and were historically Black neighborhood.
Research Questions
- Is it possible to establish a positive link between historical city planning policies and heat vulnerability by using 20th-century city planning documents, maps, comprehensive and neighborhood plans, and historic census data in the absence of an official HOLC “redlining” map?
- If it is possible to establish this link, can one be found in Cincinnati – did neighborhoods that currently have higher heat vulnerability rates historically receive more UHI-enabling developments, and if so, were they historically Black neighborhoods.
Methodology
Identified City Plans
Four citywide plans were influential in shaping Cincinnati’s urban form between 1900 and 1980 – a period in which the urban planning profession was in its early stages, and cities around the country began rapidly decentralizing (Platt, 2014). The chosen citywide plans are:
- The Kessler Citywide Park Plan (1907)
- The Official Plan of the City of Cincinnati (1925)
- The Metropolitan Master Plan (1948)
- The Coordinated City Plan (1980)
Right: The 1907 Kessler Park Plan for Cincinnati. ( Source)
Quantifying Changes to Urban Form
This research will identify how the 20th century plans have influenced neighborhoods' varying heat vulnerability by quantifying urban form factors relevant to the Urban Heat Islands. The quantified factors (Figure 2) will measure various urbanization elements that have decreased the amount of natural vegetation land cover (Mitchell & Chakraborty, 2015) and increased the production of anthropogenic heat within neighborhoods (Voelkel, Hellman, Sakuma, & Shandas, 2017).
Each of the chosen plans will be evaluated based on the following proposed changes to urban form:
- Roadway & Pavement Density
- Greenspace Density
- Land Use Mix
Though other factors impact urbanization of cities and heat island mitigation, this evaluation is based on the availability of consistent and comparable data throughout the 20th century.
Sociodemographic Analysis
Lastly, this research seeks to understand why certain neighborhoods have been selected for specific forms of development. As discussed by Hoffman et al. (2020), the practice of redlining was used to target disinvestment in non-white and low-income communities, resulting in decreased property values. Similar to the work of Hoffman et al. (2020) and Wilson (2020), this research will investigate the relationship between residents’ race and the planning policies that influenced their neighborhoods.
Through the qualitative data and neighborhood descriptions accompanying redlined neighborhoods, researchers have connected the policy to the evident racism. However, a further analysis will have to be completed to determine if there is a similarly evident relationship between proposed city and neighborhood plans and the neighborhood’s racial demographics.
Using historic census tracts and corresponding demographic data between the years 1900 and 2010 obtained from the Integrated Public Use Microdata Series (IPUMS) National Historic Geographic Information System (NHGIS), this research will better understand the chosen four neighborhoods' racial makeup.
Similar to Wilson’s demographic analysis, race and ethnicity will be measured as the percentage of Black residents. It is expected that the communities that have had historically higher percentages of Black residents were also selected for the location of more development strategies that lead to intra-urban heat islands. In contrast, areas that are less vulnerable to heat will probably have seen long term investment in their parks, greenspace, tree canopy and will have been historically White residents.
The proposed adaptation of existing research will provide an in-depth, alternative framework for planners looking to contextualize the impact of 20th-century planning and development policies on modern intra-urban heat islands. Though there is an increase in research and data visualizations centered around the implications that redlining has had on cities’ urban form, there is a lack of research focused on other planning policies, such as land use and zoning. This research proposes a method of measuring the impact that historic plans have had on modern heat vulnerability by rating their influence on urban form factors. Additionally, the proposed research will evaluate four neighborhoods' racial makeup to determine if city plans have, in a similar effect to redlining, negatively influenced non-white communities compared to historically white areas. This research intends to provide a method and comprehensive case study, allowing planners to understand the long-term impacts that policies have on neighborhood residents and contribute to inequitable public health and environmental factors in subsequent generations.
