A recent study by NASA published in the journal Sustainable Cities and Society has shown that due to an effect called the “urban heat island,” temperatures are often ten degrees higher in cities than in surrounding areas due to the heat absorption and retention of materials like asphalt and concrete.
According to the World Economic Forum, for a long time researchers have been encouraging the replacement of tar and other dark-colored materials used in roofing. New research by climate scientists from New York’s NASA’s Goddard Institute for Space Studies (GISS) reveals that bright rooftop gardens that reflect the sun or “green roofs” can alleviate some of the extreme city heat.
In the context of more frequent heat waves and more extreme heat, it’s important to understand how these urban design interventions can be effective.
Christian Braneon, study co-author
The GISS research team looked at satellite images of three green rooftop sites that had been installed in Chicago in the early 2000s and compared them to images taken between 1990 and 2011. They looked at how much surface temperatures and vegetation had changed at the sites and in control sites nearby that didn’t make use of green roofs.
The results suggested that the success of the green roofs in reducing temperatures may be determined by the diversity of the plants used, location and other factors. Temperatures were reduced in two out of three of the green roofs. The green roof that did not reduce temperatures was installed on a Walmart that had been built on a vacant lot with grass, so the amount of vegetation actually decreased when the store was built.
According to Garden and Design, any roof can accommodate a green roof, while a rooftop garden is generally heavier and uses space in different ways. A roof with a flat surface is often required. Rooftop gardens are usually set up to house a mixture of plants, trees, flowers and grasses. On the other hand, green roofs are lighter and easier to install because of the size of the plants and the trays that are used.
My hope would be that the methods we proposed show a low-cost way for folks working in less-resourced cities
Kathryn McConnell, lead author of the study
According to NASA, factors that can influence the effect of the green areas can depend on the structure of the roof itself, the diversity of plants selected and the region where the building is located,
High temperatures are often felt in neighborhoods that have less green spaces and trees, and this happens disproportionately among communities of color, as well as older adults and low-income communities, reports the World Economic Forum.
