NASA looks into the efficacy of green roofs in urban settings

The summer heat is on its way back, charging city planners with the task of keeping buildings cool
Published: Apr. 13, 2022 at 8:56 AM EDT
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GREENVILLE, N.C. (WITN) - Over the past decade, most cities in the U.S. have experienced their hottest summers on record. This trend of record breaking heat can be directly attributed to climate change, but urbanization also plays a role. A recent study by NASA’s Goddard Institute for Space Studies (GISS) looked at the effectiveness of rooftop gardens in reducing air temperatures.

The team took to Chicago for the study. They looked at three different buildings featuring different types of green roofs, intensive (deep soil, wide variety of plants, trees included) and extensive (shallow soil, low-maintenance plants). Two of the three buildings featured intensive gardens with the other building, a Walmart shopping center, going with an extensive garden.

Results from the study were mixed, expected with the small sample size. The first building, Millennium Park, with an intensive garden saw “significantly lower average temperatures” since the garden was started. Out of the three, it was the lone site that fully mitigated the rise in surrounding temperatures over the period of the study. The second intensive rooftop garden, located on the roof of City Hall, did have lower temperatures than the surrounding area, but the temperatures did show a rising trend at the end of the study.

Construction is almost finished on the Illinois Department of Agriculture Building roof which...
Construction is almost finished on the Illinois Department of Agriculture Building roof which is being transformed into a 22,000-square-foot roof covered with live plants and solar panels at the Illinois State Fairground in Springfield, Ill., Wednesday, June 23, 2010. This is part of a $1.8 million project to replace the old, badly leaking roof with an energy-efficient and environmentally friendly installation. (AP Photo/Seth Perlman)(Seth Perlman | ASSOCIATED PRESS)

The third site, Walmart, was recently built and this caused problems in the study. The large paved parking lot and connecting roads that were previously full of vegetation essentially canceled out the temperature loss brought on by the green roof.

“In a lot of places, you might be developing an area that didn’t have something there before; it just had overgrown vegetation. You might think that putting a green roof on your new building would make a significant impact. 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,” said Christian Braneon, who co-leads urban research for the Climate Impacts Group at GISS.

While the results of this study were inconclusive, the overall goal is to educated urban planners and civil engineers about how to build in an efficient and environmentally friendly manner. “Traditionally, civil engineers and urban planners assumed a stationary climate,” Braneon added. “The whole practice is built on the premise that we can look at the past to assess risk in the future. Everything is being flipped on its head due to climate change, so I’m hoping to do more work that changes how civil engineers and urban planners practice.”

For more information on this study, you can go here.

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