The Urban Heat Island effect occurs in metropolitan areas around the world. These areas normally have less vegetation for shading and evaporative cooling, more dark surfaces such as pavement, roads, parking lots and roofs and more thermal mass among the buildings in the area. This all adds up to higher air temperatures in the cities compared to the surrounding suburban areas. The difference can be as much as 12 F higher temperatures due this heat island effect in the cities. The higher air temperature has a negative impact on the formation of smog, which creates health issues, and creates a higher demand for air conditioning in the city buildings.
Replacing dark roofs with cool metal roofing can help to mitigate the urban heat island effect. The reflective nature of a cool metal roof can reflect more of the solar energy away rather than absorbing that energy which would otherwise result in warmer roof temperatures. Studies have found that cool roofing, along with other actions, can be part of the challenge to lower urban ambient temperatures, and mitigate the heat island effect in those areas.
According to geographical studies, approximately half of the world’s human population lives in urban areas. By 2030 it is estimated that the global rate of urbanization will increase by 70%. With the increase of the population moving to urban areas it is no wonder there will be impacts on the environment including pollution.
"Considered to be a cumulative effect of all these impacts is the UHI, defined as the rise in temperature of any man-made area, resulting in a well-defined, distinct "warm island" among the "cool sea" represented by the lower temperature of the area’s nearby natural landscape. Though heat islands may form on any rural or urban area, and at any spatial scale, cities are favoured, since their surfaces are prone to release large quantities of heat. Nonetheless, the UHI negatively impacts not only residents of urban-related environs, but also humans and their associated ecosystems located far away from cities. In fact, UHIs have been indirectly related to climate change due to their contribution to the greenhouse effect, and therefore, to global warming."
- Source www.urbanheatislands.com