Urban heat islands: Building cities differently to reduce heat stress

The increased absorption and retention and heat by concrete and other building materials in comparison to natural land cover creates "urban heat islands" that remain hotter than the surrounding countryside. This effect leads to elevated nighttime minimum temperatures to an even greater extent an elevations in daytime maximums, both of which contribute to greater risk for heat stress in urban populations. Substituting more reflective roofing materials for asphalt roofs can dramatically reduce temperatures. Some areas are also installing "green roofs" with native vegetation, to mitigate temperature increases. Increasing urban planting is another strategy employed to mitigate the urban heat island effect. These measures, in addition to reducing heat stress, can also reduce ozone formation, leading to additional health benefits