Heat Islands and Race in Washington, D.C.

By Dylan Basescu

When it comes to heat, not all neighborhoods in Washington, D.C. are created equal. In denser areas of the city with less wind, less green space, and less tree cover, heat radiates and is trapped at much higher rates that vary the ambient air temperature by up to 16 degrees Fahrenheit. This phenomenon is known as the urban heat island effect. This difference means different energy bills, emissions levels, health outcomes, and quality of life for thousands of residents. The District of Columbia has already noted this issue and implemented some programs to mitigate the heat island effect. However, D.C. can do more to mitigate heat islands in the most impacted communities in the District by expanding permeable surface replacements, creating a legal standard for tolerable heat, and installing new green roofs and roads in new construction.

Racial Segregation and Heat

Across the United States, racial minority-majority neighborhoods experience disproportionately high temperatures.¹ These disparities are not a coincidence. They have arisen due to racist policies of redlining and credit restrictions that segregated Black and other minority populations away from white populations. In Washington D.C., this history of discrimination has resulted in heat distributions which follow patterns of de facto racial segregation. 

The racist effects of this disparity are substantial. People in hotter neighborhoods are more likely to suffer life-threatening long term health issues, and babies born and raised in these neighborhoods are more likely to suffer health complications no matter where they move later in life due to the impacts of extreme heat on maternal stress.² Residents of predominantly Black neighborhoods are more likely to experience higher temperatures and less able to avoid or manage the effects of extreme temperature events.

The Heat Sensitivity Index considers concentrations of socially vulnerable populations. The Heat Exposure Index considers local environmental conditions that affect ambient air temperature.

In addition to health effects, excess heat also creates racially disparate impacts on water quality, electricity access, and wildlife. In summer, this excess heat can sharply increase demands for air conditioning, resulting in localized blackouts and brownouts. In the Anacostia River, warmer water runoff has contributed to a diminished dissolved oxygen content and the death of aquatic life. Combined with higher ambient air temperatures, warm water runoff heats the Anacostia River in a way that disproportionately impacts racial minority residents, particularly minority residents who rely on Washington D.C.’s internal river networks for recreation, subsistence, and income. It is urgent as a matter of health and racial equity that the district address the urban heat island effect with strategies targeted where the problem is most severe.

By targeting heat island mitigation policies at areas experiencing more intense heat and severe health impacts, Washington, D.C. can create more equitable climate conditions. This work presents three potential avenues for increasing the equitable distribution of heat. First, the D.C. government can expand the Permeable Surface Rebate Program (PSRP) to mandate greater participation by landlords. Second, it can adopt a legal standard of tolerable heat that defines tolerable heat conditions and triggers intervention where temperatures exceed tolerable levels. Third, it can mandate the use of cool or green roofs and cooling pavements on new buildings and roads.

1. The Permeable Surface Rebate Program

In higher density residential areas where landlords are less likely to make improvements to properties, impermeable surfaces like asphalt and concrete radiate heat and exclude groundwater from cooling subsurface soils. By doing more to encourage property owners to replace these impermeable surfaces with permeable surfaces like brick, cinderblock, and stone that reflect heat and absorb rainwater into the ground, the D.C. government can mitigate the disproportionate burdens of heat islands on marginalized communities. Specifically, the D.C. government can increase equitable heat distribution patterns by expanding tenant access to the Permeable Surface Rebate Program (PSRP). The PSRP grants up to $4,000 per property for replacements of impermeable surfaces with vegetation and permeable surfaces. This program offers either $5 or $10 of rebate per sq. ft. of replaced impermeable surface depending on the type of replacement. The program is only available “for properties located within Wards 7, 8, and/or the Municipal Separate Storm Sewer System (MS4) Area.”³

A map of the areas eligible for the PSRP, with areas in blue eligible for the program.

However, because the PSRP is currently an opt-in program, tenants cannot force their landlords to renovate properties as part of the PSRP. D.C.’s residential tenants should therefore be empowered with the right to compel landlords to participate in the PSRP on the same terms and procedures as if the tenant had applied for the PSRP as the homeowner. This proposal would apply equally to multi-unit and single-unit buildings, with the requirement that at least one tenant submit a PSRP application in compliance with PSRP procedures and funding availability. 

This reform would motivate landlords to remove impermeable paving surfaces from rental properties proactively and would give tenants more control over the habitability of their homes. To balance the interests of tenants against the property interests of landlords, the city should remove the $4,000 cap on the PSRP rebate so that personal homeowners and landlords can fully benefit from the rebate when replacing paving materials in proportion to the entire benefit that these replacements provide to the environment. This would make impermeable surface renovations more economical, particularly in poorer areas where large-scale impermeable surface replacements might not otherwise be viable at an un-rebated cost of between thirty and forty dollars per square foot.

2. A Legal Standard for Tolerable Heat

The D.C. government can adopt a legal standard for tolerable heat for public planning decisions and building regulations. “In the United States, minority groups suffer an elevated rate of mortality and morbidity during extreme heat events (EHEs), with African Americans being the most vulnerable group.”⁴ Despite this reality, the law still does not adequately protect vulnerable communities from heat hazard threats. D.C. can adopt solutions implemented in some other jurisdictions with large urban populations and frequent EHEs.

Borrowing from California’s Global Warming Solutions Act of 2006, Washington, D.C. can add to its heat mitigation strategies by (1) using recently gathered data to “create an urban heat island effect index” that allows city planners and the public to quantify and measure their progress across the city and (2) implementing “cooling mechanisms into land use planning, specifically for areas with dense building and transit corridors” where heat islands are particularly intense. Among a variety of options, these cooling mechanisms could include building plan requirements for green space, irrigation, and shaded areas in downtown areas. Aside from structural reforms, Washington, D.C. can regulate heat conditions in workplaces by requiring cooling personal protective equipment for workers in outdoor environments where the city declares a heat emergency or when workers are operating in especially hot areas. This would prevent manual laborers from suffering excessively higher temperatures than office workers who benefit from air conditioning. Although a single maximum tolerable temperature cannot account for diverse health and infrastructure circumstances across the city, Washington, D.C. can set regulatory targets and specialized mitigation policies for especially hot areas.

3. Green Roofs and Roads

The D.C. government can mandate the use of green or cool roofs and cooling pavements in new buildings and road replacements. These changes would mirror prior amendments to the municipal code that have imposed green requirements on new buildings and would further apply to asphalt roads. “A green roof—also called a vegetated roof or eco-roof—is a roof with soil and plants placed on top of a conventional roof.”⁵ Doubling the urban vegetation cover in the district from approximately 10% to 20% by adding green roofs to buildings would lower temperatures in the district by approximately 0.5 °C.⁶ While this may not seem significant, this change would contribute to a 7% reduction in heat-related mortality in the district during extreme heat events that would save roughly two lives in the district every year, with a particular impact on populations especially vulnerable to heat.

The left image shows the projected impact of increasing reflective roofs and roads in the district during an extreme heat event in June of 1997, while the right shows the projected impact of increasing reflective roofs and roads and increasing green roofs during the same period.⁷

However, the marginal cost of installing a green roof instead of a standard roof is $161-$215 per sq. meter.⁸ In light of the lower costs associated with requiring cool roofs, which are not vegetated but are covered in a reflective coating, the D.C. government may wish to consider mandating or incentivizing cool roofs as an alternative.

Whichever option is preferable, both are well-complemented by a mandate to install reflective and cooling pavements in all replaced road segments where possible. This policy would substantially decrease the amount of heat radiated by city surfaces if implemented at scale, particularly on road surfaces more urgently in need of repair and replacement in poorer areas of the district.⁹ In addition to mitigating heat islands, cool pavements have the potential to reduce stormwater runoff like the kind which contributes to river pollution and habitat destruction, lower tire noise from passing vehicles, and increase road safety in rainy and snowy conditions. The D.C. government should explore all innovative road technologies to determine which are best suited to various locations in the city. As existing roads inevitably deteriorate over time, the city should take the opportunity to replace them with roads that combat the urban heat island effect.

Confronting the Past, Repairing the Future

Washington, D.C. has an opportunity to right the racist wrongs of the past. Historic federal and municipal policies have created significant socioeconomic disparities in the distribution of urban heat islands, but modern policies can eliminate these disparities and create a cooler environment for every resident in the city at a time when climate change makes this intervention even more urgent. Washington, D.C. can learn from innovations in other municipalities to protect their vulnerable and marginalized populations from the health effects of extreme heat. It can also mandate reforms in construction, housing, and city planning to make sure that the city is temperate and resilient in a period of increasing climatological instability. By focusing on racial and health equity in combating the heat island effect, Washington, D.C.’s government will create a safer city for all its residents.

Footnotes

1.  See Susanne Amelie Benz & Anne Burney, Widespread Race and Class Disparities in Surface Urban Heat Extremes Across the United States, 9 Earth’s Future 7 (2021). ↩︎
2. See id. ↩︎
3. Department of Energy and Environment, Riversmart Permeable Surface Rebates. ↩︎
4. Ashley M. Gregor, Toward a Legal Standard of Tolerable Heat, 44 Colum. J. Envtl L. 479, 492 (2019). ↩︎
5. U.S. Environmental Protection Agency, EPA 430-S-18-001, Estimating the Environmental Effects of Green Roofs: A Case Study in Kansas City, Missouri 1 (2018). ↩︎
6. See Dr. Laurence S. Kalkstein et al., Assessing the Health Impacts of Urban Heat Island Reduction Strategies in the District of Columbia, Global Cool Cities Alliance, 2013. ↩︎
7. See id. at 14. ↩︎
8. See Patrick E. Phelan et al., Urban Heat Island: Mechanisms, Implications, and Possible Remedies, 40 Annu. Rev. Environ. Resour. 285, 301 (2015). ↩︎
9. See Kalkstein et al., supra note 6. ↩︎

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