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What Can Be Done About Urban Heat Islands?

NASA is interested in how urban heat — its causes, solutions, and impacts on vulnerable communities — can figure into community planning solutions and policymaking.

Low income areas in cities tend to be more densely populated and have more heat absorbing materials, such as parking lots, buildings, and sidewalks. Known as urban heat islands, these areas often don’t have room for trees that provide the necessary shade to keep temperatures cooler.

The absence of vegetation in urban areas contributes to the establishment of the urban heat island, markedly increasing thermal stress for residents and driving morbidity and mortality. Characteristics of the built environment, such as green space, urban form, city size, or spectral reflectance, not only create temperature differentials between urban and surrounding rural areas but also contribute to intracity temperature variation.

Mitigation strategies are clearly needed to reduce urban heat, particularly against a background of urbanization, anthropogenic warming, and increasing frequency and intensity of heatwaves.

Warming temperatures due to climate change are projected to increase the frequency, intensity, and length of heatwaves globally. While higher temperatures make everyone uncomfortable, vulnerability to extreme heat is disproportionately elevated among older populations, people who struggle daily with preexisting conditions, and those with limited resources to cope with days-long heatwaves. The Intergovernmental Panel on Climate Change has identified the “increasing frequency and intensity of extreme heat, including the urban heat island effect” as a relevant hazard for certain age groups — the elderly, the very young, and people with chronic health problems.

Mitigating urban heat island issues is a matter of public health and environmental injustices.

What Kind of Research is Being Done to Reduce Urban Heat?

One study evaluated the potential of green infrastructure as an urban heat mitigation strategy, focusing on greenery in parks, roofs, and walls. Typically, greenery on the ground reduces peak surface temperature by 2–9 °C, while green roofs and green walls reduce surface temperature by ~17 °C, also providing added thermal insulation for the building envelope. However, the cooling potential varies markedly, depending on the scale of interest (city or building level), greenery extent (park shape and size), plant selection, and plant placement.

Another study investigated public participation in heat impact reduction by analyzing adaptive behaviors, familiarity with urban heat island and cooling strategies, the perceived urgency of heat impact actions, and citizen’s willingness to pay. A third study added to this foundation by analyzing the overexploitation of water resources and overuse of impermeable materials. Both suppress the replenishment of groundwater and increase surface runoff, leading to urban heating, thus threatening the safety of the local population.

Results indicate that much work remains to be done, and policy and technology are often developed in isolation of each other and not in conjunction. Therefore, they have limited synergistic effects when aimed at solving global issues like urban heat.

NASA Research Will Address Vulnerability to Extreme Heat in Cities

A new NASA-funded project will support the development of an internet-based design and planning-decision support platform that will help equitably address urban heat management at the building, neighborhood, and city scales.

The lead researcher: Travis Flohr, assistant professor of landscape architecture in the Penn State College of Arts and Architecture’s Stuckeman School, is a co-principal investigator on the two-year, $250,000 project. Flohr’s role in the research focuses on devising scenario planning tools to develop tree planting programs as part of heat mitigation strategies.

What’s the big deal about urban trees? Green infrastructure acts to cool the urban environment through shade provision and evapotranspiration. Evapotranspiration –the process by which water is transferred from the land to the atmosphere by evaporation from the soil and other surfaces and by transpiration from plants — in extreme urban heat scenarios helps cool the environment.

Purpose: The project seeks to establish processes that incorporate the science of urban heat – its causes, solutions, and impacts on vulnerable communities – into community planning solutions and policymaking.

Of particular interest: Essential questions that drive the project are: What does it take to get trees to grow, survive, and thrive in urban areas? How should the street environment, also referred to as streetscape, be constructed to mitigate heat?

Data for decisions: Instead of the common result of research studies to provide analysis-ready data, this project intends to produce decision-ready data. That result is different, in that data will be ready and digestible for the actual people who make decisions about the best steps to take to mitigate heat. No longer will outside experts be needed to aid in data interpretation.

What’s the tech behind the talk? The research team is planning to develop a data-driven tool that urban developers can use to make decisions about where to invest. It will guide resources to strategically reduce and offset the effects of urban heat islands, those spaces where temperatures are much higher than outlying areas. The tool would also be used by planners writing policy, zoning codes, or building code requirements so they could apply the strategies in broader, systemic ways.

Don’t all city spaces have the same heat? Case studies of individual cities suggest that heat exposure, like other environmental stressors, may be unequally distributed across income groups. Affluent areas in cities have adequate space for trees. Those trees tend to be older, bigger, and provide more shade. Affluent communities often have a lot fewer concerns with urban heat islands.

What’s redlining? The term “redlining” refers to a Federal Housing Administration (FHA) practice. Following the Great Depression, areas with sizable populations of people of color were outlined in red ink on mortgage maps. These warnings not to approve loans to those residents meant that subsidies went to builders who were mass producing subdivisions for white, affluent people.

What does redlining have to do with urban heat? It’s been determined that the hottest places in cities are historically redlined communities. As a result, people in these communities are still exposed to higher urban temperatures and experience greater health risks from extreme heat events. In fact, in a survey of 108 US cities, neighborhoods that were redlined in the 1930’s have summer surface temperature profiles that are significantly higher than other coded residential areas.

How does scale come into play? By moving from unit scale to the building scale to the parcel scale, landowners, building owners, and renters who come into an area prone to heat island effect would have access to data. That means they’d be able to see what they could do themselves to cool things down. Maybe it would start with installing a cool roof, planting trees, or constructing a green wall. The data would also identify where the best values exist for investing in their space.

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Written By

Carolyn Fortuna (they, them), Ph.D., is a writer, researcher, and educator with a lifelong dedication to ecojustice. Carolyn has won awards from the Anti-Defamation League, The International Literacy Association, and The Leavy Foundation. Carolyn is a small-time investor in Tesla. Please follow Carolyn on Twitter and Facebook.


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