Roof Gardens Shown To Counter Urban Heat Island Effects

Heat is often intensified or amplified in cities, a phenomenon known as the urban heat island effect. Asphalt, concrete and similar materials absorb and retain significantly more heat than vegetation, so temperatures in urban areas are often 5°C hotter than in surrounding suburbs or rural regions.

In neighbourhoods with fewer trees and green spaces, this heat often disproportionately affects older adults, low-income communities and some communities of colour.

A team at Nasa’s Goddard Institute for Space Studies (GISS) have used freely available satellite data to measure the effectiveness of architectural changes designed to reduce urban heat. These include replacing black tar and other dark-coloured roofing materials with bright, Sun-reflecting surfaces or “green roofs” full of plant cover.

Green roofs are designed to harness the cooling power of plants to lower the temperature in city spaces. The greenery may be extensive (shallow soil, low-maintenance plants) or intensive (deeper soil, more diverse plants and trees).

The team studied three sites in Chicago to see how green roofs affected surface temperatures around those buildings and whether there was a difference between those sites and others nearby without green roofs.

Two of three green roofs in the study reduced temperatures, but results indicated that effectiveness may depend on location and plant diversity, among other factors.

“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 GISS climate scientist.