ABSTRACT
There are four primary ways to mitigate and adapt to extreme heat in cities: brightening albedo, ventilating urban canyons, reducing waste heat and creating cool micro-climates. The first two strategies are discussed in this chapter. Much of the urban landscape is made of hard, dark-colored materials and devoid of vegetation. So, most of the incoming solar energy is absorbed by the surface layers of buildings and pavements. Albedo is the percentage of radiation reflected back as given by the Solar Reflectivity Index (SRI) or solar reflectance (SR). This metric is thermally very significant, because most of the solar radiation that hits light-colored surfaces is reflected directly back into space before it gives up any of its heat. Morphology refers to urban canyons, which trap heat in their confined spaces. As a function of height and width, they entrap radiant heat and slow cooling winds. If wider and lined with lighter-colored surfaces and vertical plantings, the canyons are cooler. Beijing is considering tearing down tall buildings to open up wind corridors to better flush out air that is polluted, a policy that will also reduce the build-up of stagnant heat in street canyons.
