Keeping cities cool by countering the Urban Heat Island (UHI) effect – where heat from millions of homes, cars and businesses is unable to escape into the surrounding environment, increasing the temperature of city centres by several degrees and creating high energy demands and health problems – has become a major focus for urban hubs around the world. Countless solutions have been proposed, one of which, the installation of ‘green’ or ‘cool’ rooftops – using plants or high albedo surfaces to reduce solar absorption and mitigate the build-up of excess heat – appears to be increasingly gaining traction. New research conducted by the city of Chicago and the University of Notre Dame’s Environmental Change Initiative finds that these innovative rooftops could reduce the impact of the UHI by as much as 8°C.
“The lessons learned from this will be integral for city planners as they decide how green infrastructure should be implemented”
Chicago’s most high-profile foray into green rooftops came at the turn of the millennium, when Illinois-based ecological design company Conservation Design Forum installed more than 20,000 native, cultivated and non-native plants, comprising more than 150 species, atop the roof of City Hall. It was an award-winning project which utilised water harvesting and recycling for irrigation. The latest research indicates that by following City Hall’s lead, the rest of the city’s metropolitan area could enjoy a drop in peak daily temperatures of 2-3°C, or even as much as 7-8°C in downtown regions during the hot summer months, significantly nullifying the UHI.
‘The lessons learned from this will be integral for city planners as they decide how green infrastructure should be implemented,’ explains Harindra Joseph Fernando, Professor of Civil and Environmental Engineering and Earth Sciences at the University of Notre Dame. One of the key purposes of the study has been to support the Chicago Wilderness Green Infrastructure Vision plan for 2040, a collaborative set of policies to support conservation and restoration decisions in the region.
However, researchers also hypothesise that the mass installation of green and/or cool rooftops could consequently reduce the inflow of air off nearby Lake Michigan, causing the city’s air to stagnate, and potentially exacerbating a new set of urban problems revolving around air quality.
This was published in the August 2016 edition of Geographical magazine.