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Heat Islands

Heat Island Newsroom

Two men and one woman in a park with trees read from a clipboardWelcome to EPA's Heat Island Newsroom, which includes recent issues of the Heat Island Newsletter and other notable news items. Older newsletters can be found in the Newsroom Archive. To receive the newsletter and notices of heat island-related conferences by email, sign up for EPA's Heat Island Newsletter.

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September 6, 2018 Newsletter

General Heat Islands

  • Reduced Heat Island Intensity under Warmer Conditions – Researchers from John Hopkins University recently published findings that the intensity of the heat island effect decreases as temperature increases. They studied 54 locations in the United States from 2000 to 2015, looking at the daily minimum and maximum temperature differences between paired urban and rural weather stations. The difference in rural and urban temperatures decreased with temperature increases in 70% of the locations. The researchers find that the results are driven by changes in rural temperatures rather than urban temperatures.
  • Baltimore, Maryland cityscapeVolunteers Map Heat Islands in Washington, DC, and Baltimore, MD – A project led by the National Oceanic and Atmospheric Administration is using volunteers in vehicles equipped with special thermometers to determine which areas of Washington, DC, and Baltimore, MD, are the hottest. This information could identify which communities need assistance during heat events, or where investments are needed for cooling strategies, such as cool roofs or green roofs.
  • From Los Angeles, CA, to Louisville, KY, U.S. Cities Seek Heat Island Solutions – As warming trends become more pronounced, large cities must find solutions to resurface the urban environment, slow the rate of warming, and protect public health. Researchers encourage cities to think beyond a single solution, and pursue a palette of strategies including the use of shade trees, walkable corridors, and altering land and energy use decisions.
  • The High Cost of Hot – Cooling degree days (CDDs) are used to estimate the amount of artificial cooling needed to maintain a comfortable indoor temperature. A new report by Climate Central, an independent organization that focuses on climate research, profiles how an increase in daily minimum temperatures, and CDDs in particular, are associated with higher energy bills from the use of air conditioning. The report explores changes in 211 cities in the United States; 93% have seen an increase in CDDs since 1970, including cities with more moderate climates. Much of this increase is attributed to increased low temperatures at night.
  • New Video Succinctly Describes the Heat Island Effect – The online video produced by National Public Radio gives a quick overview of the heat island effect that is suitable for a majority of audiences.

Heat Waves

  • Keeping Cities Cooler during Heat Waves – A recent news article in The New York Times profiles several strategies for cities to prepare for and cope with heat waves. It points to some lesser-known strategies including the creation of ventilation corridors that restrict the construction of buildings in certain locations, permitting unrestricted air to flow and bringing down nighttime temperatures. Preparing for blackouts can also help cities cope with heat waves and protect public health.
  • Buildings Feel the Heat, Too – Researchers from Arizona State University looked into how buildings constructed to comply with building energy codes fared in a hypothetical three-day power outage. They found that in most climates, indoor conditions became too hot to be considered safe for occupants. However, they observed a link between building energy efficiency and resiliency to heat – more energy efficient buildings fared better in warmer climates.

Green Roofs

  • Portland Integrates Green Roofs as Part of City Plan – Portland, OR, recently adopted the Portland Central City 2035 Plan with a mandate for vegetated roofing on buildings larger than 20,000 square feet. A cohort of partners evaluated this component of the new plan; they include the Green Roof info Think-tank (GRiT), Green Roofs for Healthy Cities, Greenroofs.com, the Audubon Society, and Portland State University.
  • Sprinkler spraying purple and red flowersIrrigation Improves the Cooling Benefit of Green Roofs – In a research article featured in Building and Environment journal, researchers modeled the effectiveness of green roofs under different irrigation scenarios. Green roofs with moderate irrigation reduced excess heat by 15-51% compared to conventional roofs, and green roofs with unrestricted irrigation reduced excess heat by 48-75% compared to conventional roofs.

Green Infrastructure

  • New Green Infrastructure and Health Guide – A new guide produced by the Willamette Partnership, the Oregon Public Health Institute, and the Green Infrastructure Leadership Exchange explores the linkages between green infrastructure and public health. The guide provides best practices about how to use green infrastructure to promote health equity including identifying community health needs, making the business case for health and green infrastructure, engaging the public, siting and designing projects, and evaluating health benefits.
  • Literature Review of the Cooling Effects of Green Infrastructure – A literature review published in Solar Energy takes a compressive look at how cooling effects of green infrastructure are documented in published literature. The authors evaluated 165 studies from 2010-2017 on a range of criteria including geographic focus, benefits analyzed, and type of green infrastructure. They found a number of gaps in the literature including oversight of the cumulative effects of green infrastructure. They also noted the green infrastructure field could benefit from standard protocols or classification systems.

Cool Roofs

  • Effect of Cool Roofs at a Neighborhood Scale – Researchers from Lawrence Berkeley National Laboratory published the results of a theoretical analysis, modeling the potential impact of a neighborhood-scale cool roof demonstration project on air temperature. Their results show a potential reduction in air temperature ranging from 0.5°C to 1.3°C, depending on the heat transfer analysis method used. They caution more modeling is needed before beginning a neighborhood-scale demonstration project.

Trees and Vegetation

  • U.S. Urban Tree Cover Declining – Researchers from the U.S. Forest Service report that the United States might have lost as many as 36 million trees per year from 2009 to 2014. The researchers used aerial photography to compare land cover changes in urban areas across the entire United States. They found that tree cover is declining at a rate of 175,000 acres per year. Jurisdictions with the greatest decline in tree cover, in descending order, were Oklahoma, the District of Columbia, Rhode Island, Oregon, and Georgia, coinciding with a gain in impervious surface cover. They note the range of benefits that urban forests provide, and consequently recommend integrated programs that focus on sustaining tree canopy.

Public Health

  • Washington Square Park in NYC with archway and large fountainCool Neighborhoods in New York City – In New York City, officials in the Office of Recovery and Resiliency, Health Department, and partner organizations are working together to protect public health during extreme heat events. The $106 million Cool Neighborhoods program includes painting surfaces white, planting trees, constructing green roofs, and building green infrastructure to cool specific neighborhoods. The program targets heat-vulnerable communities, such as those that lack vegetation, or have at-risk populations, such as older adults.

May 30, 2018 Newsletter

General Heat Islands

  • Bird's eye view of a gridlike city with tree-lined streetsHeat Islands and the Patterns of Cities – A study from the Massachusetts Institute of Technology found that grid-like cities had a greater buildup of heat than cities with less-orderly patterns, and that the arrangement of buildings and streets was the most important determinant of the heat island effect. According to the authors, the layout influences the way buildings absorb and re-radiate heat to surrounding structures, which may account for the temperature differences observed.
  • Mitigating the Heat Island in Gowanus, Brooklyn – Gowanus is an area of South Brooklyn, NY, with a high proportion of low-income residents and a lack of parks and greenery, factors that increase its population’s vulnerability to the heat island effect. The Urban Land Institute’s recent report proposes comprehensive heat mitigation strategies that could cool the neighborhood locally and improve health outcomes (e.g., a new park, increased tree canopy cover, and efficient building design).
  • A Zonal Model for Street Canyon Air Temperature – The buildout of cities with tall structures lining narrow streets creates street canyons, or urban canyons, that can exacerbate the heat island effect. Researchers from the University of Hong Kong and contributors recently published a new model for measuring canyon air temperatures. By incorporating three-dimensional landscapes, wind movement, and heat transfers between surfaces, the model reliably predicted street canyon air temperatures in zones with different street layouts or building height-to-width ratios. The zonal model could be used to assess the impact of these canyons on heat islands in high-density cities.

Heat Waves

  • How Do Heat Islands Interact with Heat Waves? – The heat island effect increases cities’ baseline temperature, which can exacerbate the effects of heat waves. A team of researchers led by Princeton University modeled this interaction for 50 U.S. cities. They found that the synergistic effects between heat islands and heat waves are currently most significant in eastern and southeastern cities, but projected that in the future, the effects will be more pronounced for cities in arid climates in the Southwest.
  • State and Local Resilience to Extreme Heat – The Center for Climate and Energy Solutions developed a fact sheet to help state and local officials consider emergency responses to heat waves as part of a holistic approach to managing climate risks. The fact sheet includes costs, benefits, and co-benefits of different resilience strategies like using cool pavements and increasing tree canopy cover. It also provides real-world examples from cities that have implemented these approaches.
  • Cityscape glowing in orange under the sunStudy Researches Main Cause of Future Heat Waves in United States – According to scientists from the University of Miami and the National Oceanic and Atmospheric Administration, rising temperatures will surpass natural variability as the main cause of future heat waves in some parts of the United States. The authors of the study determined this will occur in the western United States by the late 2020s and in the Great Lakes region by the mid-2030s.

Cool Roofs

  • Cool Roof Rating Council’s (CRRC’s) New Online Rating Portal for Roofing Products – CRRC evaluates the solar reflectance and thermal emittance of roofing products, which helps roofing manufacturers and purchasers meet heat island reduction and building energy-efficiency goals. In April 2018, the CRRC Product Rating Program launched its new online rating portal. This new portal streamlines the rating application process and improves CRRC’s product directory. It helps manufacturers better manage their applications for obtaining product ratings, including ENERGY STAR® certification.
  • Landscape with an urban center surrounded by rural areas and farmlandReflective Surfaces Help Urban Heat Islands – and Rural Ones Too – Yale Environment 360 reported on some of the latest cool roof, green roof, and reflective surface research and technologies, which have the ability to reduce the heat island effect in urban and rural areas.

Green Infrastructure

  • Delivering Urban Resilience: Costs and Benefits of Adopting Smart Surfaces – A report written by Capital E and recently released by the U.S. Green Building Council analyzed the costs and benefits of “smart” surfaces, or surfaces that deliver a range of environmental, economic, health, and social benefits relative to conventional surfaces, across three U.S. cities: El Paso, TX; Philadelphia, PA; and Washington, DC. The authors demonstrated that smart surfaces, including green roofs, cool roofs, solar panels, and permeable and reflective pavements, offset extreme heat and extreme weather driven by warming; while also mitigating climate change, stormwater runoff, and netting billions of dollars in financial benefits.

Trees and Vegetation

  • Urban Trees and Water Availability – Researchers from Harvard and North Carolina State University previously found that the heat island effect was associated with increased pests and reduced growth of the willow oak, a common large shade tree in the southeastern United States. In a recent study, the team linked reduced tree growth to water stress, and recommended that urban forest management strategies focus on tree hydration to mitigate the effects of warming and drought.
  • Why Dallas is Warming Up and Plans to Cool Down – The 2017 Dallas Urban Heat Island Management Study from the Texas Trees Foundation, in collaboration with the Georgia Institute of Technology, found that more than one-third of Dallas is covered by impervious surfaces like concrete and commercial buildings, which absorb heat and contribute to the heat island effect. The foundation’s report provides a framework for maintaining existing trees and planting thousands of new ones to increase the city’s urban forest canopy, thereby cooling the city and cleaning the air.

February 13, 2018 Newsletter

Heat Islands

  • Urban Heat Island Effect Projected to Strengthen – In the recently released Fourth National Climate Assessment, Volume 1: Climate Change Special Report, the U.S. Global Change Research Program (USGCRP) reports for the first time a key finding that the heat island effect is responsible for higher daytime and nighttime temperatures in urban areas compared to surrounding rural areas. USGCRP projects with high confidence that the heat island effect will strengthen in the future as urban areas change and grow, and population densities increase. The report is an assessment of a large body of scientific, peer-reviewed research and is regarded as an authoritative resource on the science of climate change in the United States.
  • Vulnerable Populations and Phoenix’s Widening Heat Island – Across the U.S., urban heat puts vulnerable populations, like low-income, homeless, and elderly individuals, at higher risk of heat-related illnesses and even death. Accordingly, in Phoenix, Arizona, differences in exposure, sensitivity, and adaptation to high temperatures lead to disparate effects on the city’s residents. A range of tactics are being employed by the City of Phoenix to fight the heat and improve the health of residents: painting roofs with reflective paint, planning more trees, and implementing the “We’re Cool” program, which provides free centers for cooling off and hydrating.

Green Infrastructure

  • How to Fund Your Green Infrastructure Project – The National Recreation and Park Association published a new guide to financing green infrastructure projects. The guide includes strategies like partnering with nontraditional supporters, and folding green infrastructure projects into financing for stormwater projects. Heat island mitigation strategies to install green roofs and plant trees and vegetation are types of green infrastructure; the funding strategies in the guide could be used to advance heat island reduction projects.

Green Roofs

  • Denver Passes Green Roof Ballot Initiative – In November 2017, Denver, Colorado voters approved a modification to the city building code requiring rooftops of new buildings over 25,000 square feet to include green roofing or solar panels, with the goal of mitigating urban heat. The green roof/solar requirement increases 10 percent for every 50,000 square feet, up to a cap of 60 percent.

Cool Roofs

  • Heat Mitigation Conserves Water, Too – A study from Lawrence Berkeley National Laboratory (LBNL) found that widespread implementation of cool roofs – made of materials or coatings that reflect heat and sunlight – in California would result in cooler temperatures and also reduce outdoor water consumption. The study showed that by contributing to lower air temperatures, cool roofs reduced evaporative transpiration and evaporative water demand, therefore reducing irrigation water use.

Cool Pavements

  • Los Angeles is Coating its Streets to Fight Urban Heat – Los Angeles, California, is piloting ways to combat rising temperatures and reduce the heat island effect, including coating city streets with CoolSeal, a substance designed to reflect solar radiation. City officials linked cooler streets to cooler air temperatures, reduced air conditioning use, and decreased heat-related deaths.
  • Cost-Effectiveness of Cool Surfaces – Many cities are coating or building walls and pavements with reflective materials, but how cost-effective are these methods for heat mitigation? A study from LBNL’s Heat Island Group describes methods for quantifying some of the benefits of cooler surfaces, such as reduction in electrical energy usage and avoided carbon dioxide emissions.

Trees and Vegetation

  • Urban Forests in Canada Reduce Air Pollution and Improve Public Health – In addition to cooling air temperatures and sequestering carbon, urban trees can clean the air when particulate pollutants adhere to their surfaces and gaseous pollutants are taken up through leaves. A study from the U.S. Forest Service and Environment Climate Change Canada found that trees in 86 Canadian cities removed thousands of tons of air pollution, leading to positive human health outcomes including reduced mortality and prevention of acute respiratory symptoms.
  • Investing in Urban Trees Benefits Public Health – Trees provide a variety of ecosystem services such as heat mitigation, air purification, and recreation and tourism benefits. These advantages also result in public health and economic benefits that may not be fully understood by city planners and policy makers. A 2017 report by The Nature Conservancy provides information on the links between the health benefits of urban trees, and the finance and policy solutions cities can use to realize these benefits. For example, the authors used the EPA's CO-Benefits Risk Assessment Health Impacts Screening and Mapping Tool (COBRA) to estimate that 27 cities could each avoid $13.2 million per year in health care costs from urban tree planting.

Public Health

  • New Risk Mapping and Planning Tool – The New Orleans Office of Resilience and Sustainability and the Trust for Public Land launched a new mapping tool designed to identify priority areas for investments in green infrastructure in New Orleans, Louisiana, based on a suite of considerations such as heat mitigation and social equity. Through a partnership with the Louisiana Public Health Institute, the tool incorporates neighborhood level data for 15 health outcomes, including cardiovascular disease, respiratory disease, diabetes, and stroke. This tool was presented at the 2017 American Public Health Association meeting.