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NASA explores potential for green roofs to mitigate heat-island effect in cities

5 min read

Sustainable Planet
Source: Unsplash/CHUTTERSNAP

Using satellite imagery, NASA has found that rooftop gardens can offer substantial temperature reductions in cities.

NASA looks into green roofs as a means to lower temperatures in cities

Last month, Archinect reported on research undertaken by NASA which found that rooftop gardens can offer substantial temperature reductions in cities during summer months. In a study published in the journal Sustainable Cities and Society, the group used satellite imagery to measure temperatures at three rooftop gardens in Chicago compared to before the roof gardens were installed.

The research sought to understand ways of mitigating the “urban heat island” in cities, where the heat absorption and retention of materials such as concrete and asphalt can cause temperatures to be ten degrees higher in cites than in surrounding areas. — Archinect.

As an adaptive response to rising temperatures, many cities have begun to install vegetated ”green” roofs, which now vary widely in structure and size, and have generally been shown to have cooling capacity.
In the coming decades, millions of urban residents will be exposed to increasingly deadly heat extremes. As an adaptive response to rising temperatures, many cities have begun to install vegetated ”green” roofs, which now vary widely in structure and size, and have generally been shown to have cooling capacity. Source: Unsplash/CHUTTERSNAP

Researchers used publicly available satellite imagery and open-source software

“As cities grow and develop, they need to make good decisions about their infrastructure, because these decisions often last for 30 or 50 years or longer,” said Christian Braneon, a climate scientist and civil engineer at Columbia University and co-author of the study. “In the context of more frequent heatwaves and more extreme heat, it’s important to understand how these urban design interventions can be effective.”

In place of dark-coloured materials traditionally used on urban roofs, such as tar, the team explored the impact of bright rooftop gardens and green roofs, whose plants and greenery reflect the sun’s rays. To do so, the team selected three green roofs installed in Chicago in the early 2000s. Using publicly available satellite imagery and open-source software, the team compared aerials of the green roofs to images of the sites taken before installation. Continued below…

Source: Archinect.com

A team at NASA have devised a method to evaluate the cooling effects associated with green infrastructure that draws on publicly available satellite imagery and open-source software for analysis. Based on a quasi-experimental research design that integrates social and physical science approaches, this technique is able to identify the cooling effects of green infrastructure against background warming trends associated with urbanisation and climate change.
Little research has been done to differentiate which types of green roofs are most effective at reducing urban heat. A team at NASA have devised a method to evaluate the cooling effects associated with green infrastructure that draws on publicly available satellite imagery and open-source software for analysis. Based on a quasi-experimental research design that integrates social and physical science approaches, this technique is able to identify the cooling effects of green infrastructure against background warming trends associated with urbanisation and climate change. Source: Unsplash/micheile dot com

the benefits of green roofs are dependent on a variety of factors

The study found that temperatures were reduced in two out of the three green roofs. At one site, which contained a heavy mix of plants, average temperatures were significantly lower than before the green roof was installed in 2004.

Meanwhile, a green roof at Chicago’s City Hall installed in 2002 was found to have also lowered temperatures, though the figure has begun rising again in recent years. For researchers, the recent increases are a demonstration that the benefits of green roofs are dependent on a variety of factors, including geographic region, plant diversity, and the cooling efficiency of the building itself. Continued below…

Source: Archinect.com

finding that the study sites with larger, intensive green roofs accompanied by diverse plant species have greater cooling benefits than the extensive, monoculture green roof.
The team demonstrated this method at three green roof sites across the City of Chicago… finding that the study sites with larger, intensive green roofs accompanied by diverse plant species have greater cooling benefits than the extensive, monoculture green roof. Source: Unsplash/CHUTTERSNAP

While Green roofs are good they can not beat natural grass and vegetation on the landscape

On the third green roof, placed on top of a Walmart shopping center, temperatures have in fact increased since the green roof’s installation. While the other two green roofs were added to existing buildings, the green roof on the Walmart was constructed at the same time as the supermarket itself, built on the site of a vacant grassy lot. The team, therefore, concluded that although the building contained an extensive green roof, it was not enough to compensate for the removal of the natural grass and vegetation on the landscape.

“You might think that putting a green roof on your new building would make a significant impact,” Braneon explained. “But what we see is that a lot of impervious material may also be added there – such as a parking lot around the building. As a result, you might reduce the impact of the parking lot, but you certainly haven’t created the cooling effect that the overgrown vegetation had.”

Source: Archinect.com

This low-cost method can aid policymakers and planners in empirically evaluating the cooling capacity of green roofs in their own communities.
Everything about the new system is publicly available and therefore cheap to use. This low-cost method can aid policymakers and planners in empirically evaluating the cooling capacity of green roofs in their own communities. Source: Unsplash/CHUTTERSNAP

Bringing green growth back into cities is something Sustainable Urban Delta know all about

Sustainable Urban Delta inspire and empower cities to become food producing communities, creating a healthy and sustainable living environment. Food producing cities aren’t far away, but we need a catalyst. Sustainable Urban Delta are here to connect, enable and amplify the change out there. 

The Sustainable Urban Delta Foundation was established to inspire megacities to make choices that open the door to healthy and sustainable urban growth. A crucial element of our approach is the production of local, healthy and fresh food. This can either be done inside cities or on undeveloped agricultural land surrounding cities, known as green belts. We aim to be the catalyst and the connector in order to create a better future. — SustainableUrbanDelta 

Meanwhile in the Faroe Islands… Source: Unsplash/Annie Spratt
Make an Impact

SUSTAINABLE URBAN DELTA: BRINGING FOOD PRODUCTION INTO CITIES

What if the green belts where food is produced were integrated into urban areas? This would create exciting new opportunities on a social, ecological and economic level. But where do we start? It is not as difficult as you think. Sustainable Urban Delta is here to show the world that it is possible. Or better yet: that it’s already happening! Click through and learn more about this exciting movement and how you can be involved.