NASA’s Goddard Institute for Space Studies (GISS) has released research that suggests using rooftop gardens and greenery could combat severe heat in cities.
Researchers have endorsed replacing dark-coloured roofing materials and black tar with Sun-reflecting surfaces also known as “green roofs” for several decades. They have now got data from satellites which is freely accessible to measure the effectiveness of these changes.
A phenomenon known as the “urban heat island effect” is common in cities due to heat intensification and amplification. Materials usually used such as concrete and asphalt absorb heat like a sponge and retain it, causing temperatures in urban areas to be around -12 degrees Celsius (10 degrees Fahrenheit) hotter than in surrounding suburbs and rural areas.
Green roofs are designed to lower the temperature by using the power of plants to cool the temperature in city spaces. The greenery can range from shallow soil and low-maintenance gardens to more diverse trees, shrubs, and plants.
Three sites in the city of Chicago were studied by the GISS team and two of the three green roofs succeeded in reducing the temperatures. The study results showed indication that the location and plant diversity, among other factors would have a bearing on the effectiveness. Scientists say the benefits are dependent on rooftop structure, geographic region, and the building’s own cooling efficiency. Studies with larger sample sizes will be required to separate the details, but the study is an encouraging beginning.
The results from the study were published in the journal of Sustainable Cities and Society in January 2022 and can be found here.
Christian Braneon, a climate scientist and civil engineer at Columbia University and GISS said, “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. In context of more frequent heat waves and more extreme hear, it’s important to understand how these urban design interventions can be effective.”
Braneon and the GISS team partnered with Chicago Planning and Development department and Chicago Public health department for the green roofs study at the three sites in the early 2000s. The sites were a Walmart shopping centre, Millennium Park, and City Hall.
Imagery captured by the Landsat 5 satellite between 1900 and early 2000s was used by researchers who compared variations in the land surface temperatures and vegetation abundance at the three sites, as well as the nearby control sites that did not have green roofs installed.
Mixed outcomes resulted. The Walmart site was a newly built shopping centre during the study period and even though an extensive green roof was installed, the vegetation index for the landscape decreased due to the conversion of the land from a grass filled, vacant lot.
City Hall was an intensive site which had a green roof installed in 2002. Toward the end of the study period temperatures began to rise despite the initial temperatures being lower than those of the nearby control site.
Millenium Park was also an intensive site, containing a mix of plants in its location near Lake Michigan. This site showed significantly lower temperatures on average after the installation of the green roof in 2004. Millenium Park was the only site where the roof fully mitigated climate warming over the study period.
