urban heat island

Green Roofs Keep Urban Climates Cooler

By Thomas Landreth

Image of a green roof

Green roof

From conversations I’ve had with friends in construction: roofing is tough work. Steep angles make for dangerous conditions, metal roofing is remarkably sharp, and whatever material you work with, it’s guaranteed to be heavy.

During the summer, heat adds an almost unbearable element. This can be especially bad in metropolitan areas, where ambient temperatures combine with heat coming off numerous nearby roofs, pavement, and other elements to create an “urban heat island.”

EPA researchers and partners recently published findings in the Proceedings of the National Academy of Sciences showing how three types of roofing can help: “cool” (coated in a reflective material to eliminate heat buildup), green (vegetated), and hybrid (vegetated with reflective plants).  Hybrid roofs, which are a new concept and not yet available, would be constructed with light-colored plants that have higher reflectivity similar to cool roofs and also the advantages of green roofs, like water retention.

The authors found that any of these roofing options can have benefits by cooling urban heat islands. Thus, this helps to reduce the impacts of global climate change by cooling metropolitan regions.

Lead author Matei Georgescu, a sustainability scientist at Arizona State University, explains, “What we found for cool, green, and hybrid roofs is that they don’t just offset urban expansion—they can offset additional warming.”

Georgescu partnered with EPA scientists Philip E. Morefield, Britta G. Bierwagen, and Christopher P. Weaver, his co-authors on the study.

Through EPA’s Integrated Climate and Land Use Scenarios (ICLUS) project, researchers  had access to a wealth of modeled data focused on impacts from projected urban growth. Using these data, they explored the three methods of roofing designed to absorb less heat to compare and contrast benefits and trade-offs. What they discovered is that while all three  have positive environmental implications, green roofs have less heat-mitigating power than cool roofs (hybrid roofs cool at least as well as cool roofs alone), but cool roofs may mean that additional heating is needed during the winter in some areas.

Though roofing is a single component among major factors such as urban sprawl and carbon pollution, this study shows it can have an impact on reducing heat in large urban areas.

New roofing alternatives may offer an added component to innovative urban designs, new building styles and grid layouts created to offset urban heat islands. “Green cities” may not be a reality yet, but facets to such future cities are currently being considered and implemented. Interest in cooling down urban heat islands is growing and recently caught the attention of over 40 news outlets, including Popular Mechanics, Scientific American, Christian Science Monitor, USA Today, the LA Times, and several international newspapers.    

Although roof installation may not get any easier, green and cool roofs may soon make American’s urban hotspots cooler.

About the author: Until last week, Thomas Landreth was a student services contractor working with EPA’s Office of Research and Development. He recently accepted a new position with the American Association for the Advancement of Science (AAAS).

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action.

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Climate Change and Health: Lessons Learned from Older Americans

To continue the Agency’s efforts to expand the conversation on climate change, we are highlighting EPA climate change research with Science Matters articles. This post features research exploring the health effects of climate change and older Americans. 

Climate Change and Health: Lessons Learned from Older Americans
EPA researchers are exploring the links between climate change and health effects for older Americans. 

OldercouplestrollingClimate change is affecting a growing population of at-risk older Americans. Studies by EPA researchers and others find that seniors aged 65 and older are more vulnerable to hot temperatures and extreme weather events—effects which will become more frequent as the climate changes.

In a recent paper, “Climate Change and Older Americans: State of the Science” (Environ Health Perspect 121:15–22. 2013), EPA researchers reviewed the current “state of the science” about the links between climate change and health effects impacting older Americans.

The paper explores connections between what is expected to be an increase in the population of older Americans living in places relatively more affected by climate change. “Life expectancy has increased at the same time that we see a huge bubble of baby boomers headed into retirement. These demographic changes are happening even as the effects of climate change are becoming more widely recognized,” explains EPA economist and lead author Janet Gamble.

To assess the vulnerability of older Americans to climate change, the research team performed an extensive literature search.  From more than 400 citations identified, they selected nearly 100 papers to review that most closely addressed key terms describing characteristics of the older life stage; their vulnerability to climate-related impacts, and their overall health and well-being.

Older adults comprise 13% of the U.S. population today, but are expected to account for approximately 20% by 2040. They are also a diverse group, with differences in age, race/ethnicity, socioeconomic status, degree of community or family support, general health or pre-existing medical conditions, and disability. These differences ultimately determine the extent of older adults’ vulnerability to the impacts of climate change.

In addition, location matters.  “Older adults are retiring in areas, such as Florida, that experience a higher rate of extreme weather events,” notes Gamble, adding that more that 50% of older adults reside in only nine states, with Florida, California, New York, Texas, and Pennsylvania accounting for the top five.

Regions with higher levels of older adults, such as the five states mentioned above, are likely to be particularly at risk to changing precipitation patterns, tropical storms, flooding, and the urban heat island effect, a term describing the warming of urban areas relative to their rural surroundings due to the prevalence of buildings, roads, and other dark, heat-absorbing surfaces.

The report finds that older adults living in poverty or on fixed incomes are likely to experience greater exposure to some climate-related impacts, especially the effects of heat waves or hurricanes. Poverty is a primary contributor to social vulnerability, as financial status affects their ability to respond quickly and effectively. Older adults living in poverty can be more vulnerable to property damage and loss due to lack of insurance, limited personal finances, and poor credit worthiness.  In addition, older adults living in poverty may not have transportation to evacuate an area during an extreme weather event and may live in substandard housing, also increasing their risks.

The authors highlight a number of measures, called adaptations, that may address such vulnerability.

Such adaptations promote effective community responses to risks thought to be climate-related and may include: community support networks, subsidization of air conditioners, and community-based registries to help identify and reach those who require evacuation assistance. Similarly, planting trees or installing green roofs can reduce the urban heat island effect.

Identifying effective adaptation measures and outlining the best ways to implement them continue to be a challenge.Oldercoupletakecellphonepicture

When asked about next steps, Gamble states, “I think there is more work to be done in assessing the vulnerability of at-risk populations. As a first step, we need to communicate the climate risks experienced by older adults to decision makers, public health and safety officials, and caregivers and advocates of aging populations.  Also, in the near term, it may be possible to build on and adapt some of the response strategies developed for heat waves and hurricanes and apply them to the broader set of climate change impacts affecting older adults.”

By investigating the relationship between climate change stressors and vulnerability to at-risk life stages such as older Americans, EPA researchers are helping to inform communities and others so they can be better prepared to protect human health.

Learn More

Climate Change and Older Americans: State of the Science (Online abstract)

EPA Research: Climate Change and Health

Preparing for Extreme Heat

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action.

Please share this post. However, please don't change the title or the content. If you do make changes, don't attribute the edited title or content to EPA or the author.