Concrete albedo cools urban heat

High summer temperatures records are increasingly being broken resulting in the Government considering ways to reduce global warming. Indeed, it has recently allocated £57million to the Advanced Research and Invention Agency to examine potential ‘geoengineering’ projects that can reduce global warming by reflecting sunlight back into space.

Geotechnical trials to reflect sunlight are proposed to start in 2027. They include ‘brightening clouds’ by force spraying sea water into them. There are concerns that the use of speculative and manipulative geoengineering could result in destructive weather patterns which could worsen the impacts of global warming.

However, a new report from Britpave, the infrastructure industry association, forwards a solution that is at our feet: the solar reflectance – or albedo – of concrete roads. The report, ‘Cooling Urban Heat Islands: A Concrete Option’ explains how concrete roads can reflect 25% to 50% of sunlight and solar radiation back into space. This high albedo rating compares to asphalt roads that have an albedo rating of just 5%.

Increasingly, the use of solar reflectance is being viewed as a way to reduce global warming. This is especially the case for cooling urban heat islands. Cities are generally warmer than adjacent suburban and rural areas. For example, London can be 4OC hotter than outer areas. This can reach 10OC during extreme heat events. Excessive urban heat is recognised as being a major health hazard.

Given that roads and pavements can cover up to 40% of a city’s urban land mass, using the solar reflection of concrete can be a powerful tool to reduce urban temperatures. Research carried by the Massachusetts Institute of Technology Concrete Sustainability Hub calculated that the use of albedo reflective payments could reduce peak summer air temperatures in Boston by 1.7OC and in Pheonix by 2.1OC. In China, research into reducing urban heat temperatures in the city of Tianjin found that a reflective albedo of just 0.5 can reduce road surface temperature by 6OC.

Increasing the solar reflection of the built environment offers a powerful strategy to reduce the severity of urban heat. Concrete pavements with their high albedo rates are well placed to lead this strategy.

‘Cooling Urban Heat Islands: a concrete option’ may be downloaded from www.britpave.org.uk/publications