UHIs increase the number of very hot days during warmer months than would occur in the same location with natural land cover. Very hot days may trigger heat-related stress, illness or potentially death and are likely to increase the use of air-conditioning, resulting in raised energy requirements and air pollution from fossil fuel-generated electricity.

BlueScope Steel sustainability manager Richard Rowe said the use of BlueScope Steel’s high solar reflectance roofing materials, in combination with increased surface vegetation, is one of the most effective ways to reduce higher temperatures in urban areas.

Sustainable materials from BlueScope Steel capable of reducing surface area temperatures – such as COLORBOND® steel in the colours Classic Cream™, Surfmist® and Whitehaven®, as well as COLORBOND® Coolmax® steel with Thermatech® solar reflectance technology – can help to create more environmentally friendly communities.

The Green Building Council of Australia recognises this with credit in the Green Star Communities rating tool for mitigation of the heat island effect through the widespread use of very high solar reflectance roof materials.

UHIs refer to the phenomenon of cities and urban areas often being significantly warmer than the surrounding rural or undeveloped areas. The United States Environmental Protection Agency (EPA) reports that, on average, US cities are up to 5.6°C warmer than the surrounding countryside.

Mr Rowe said building materials including roofing can also play a vital part in lowering urban temperatures. The use of high solar reflectance roofing materials lowers temperatures, reducing the need for air-conditioning while reducing the amount of heat reflected into the atmosphere.

“Increased reflectivity of urban dark surfaces and roofs is especially effective in mitigating UHIs since more surface area can be treated this way than can be revegetated,” said Mr Rowe.

BlueScope Steel produces a large variety of roofing materials with high reflectance properties, meaning that they reduce the amount of heat energy absorbed from the sun. COLORBOND® steel in the colours Classic Cream™ and Surfmist® as well as COLORBOND® Coolmax® steel in the colour Whitehaven® are very high solar reflective roofing materials. There are also a number of colours from the standard COLORBOND® steel range and the COLORBOND® Metallic steel range, as well as ZINCALUME® steel, that are also highly reflective.

“Using these products can reduce building temperatures, allowing for less reliance on air-conditioning to maintain a comfortable internal temperature. Combining this with an increase in vegetation around buildings is an effective way of reducing the intensity and impact of UHIs,” concluded Mr Rowe.

A number of different factors can create or contribute to UHI's. These include:

1. Increased heating as a result of human activities such as industrial processes, electricity generation and vehicular traffic
2. Reduced evapotranspiration through vegetation loss. Evapotranspiration refers to the sum of water entering the atmosphere from the surface of the earth. This is reduced when vegetation, soil, water bodies and forest canopy – which bring water vapour and its cooling effects to the atmosphere – are replaced with urban fixtures. Using vegetation such as grass and plants in urban landscapes can result in temperature reductions through increasing levels of moisture being released into the atmosphere, less surface heat retention and the provision of shade to buildings and pavements.
3. Lower surface reflectivity of urbanised areas. Human-made structures and surface coverings found in urban environments have lower surface reflectivity than natural land cover, and therefore absorb more incoming solar radiation and retain more heat.