ABSTRACT
Cities tend to be warmer than their unbuilt surroundings. This effect, commonly referred to as the urban heat island (UHI), has consequences for energy use, air quality and human health. As a result, municipalities are increasingly deploying strategies to reduce the undesirable consequences associated with the UHI. These measures typically focus on reducing summertime urban air temperatures by increasing the solar reflectivity of urban surfaces and facilitating evaporative cooling by reducing impervious surface cover and adding urban vegetation. Other sustainability efforts that reduce energy use in cities also affect the urban climate by reducing waste heat and pollutant emissions. While the focus of mitigation strategies tends to be on summer air temperatures, it is important to recognize that there are other factors affecting the well-being of urban populations. These include the effects of urbanization on humidity and atmospheric mixing and the seasonal variations in the effects of UHI mitigation efforts. Thus, successful sustainability efforts must look beyond summertime air temperatures. This chapter provides a summary of the urban climate system. It discusses common urban climate mitigation strategies as well as their intended and unintended consequences. The chapter concludes with a call for a holistic evaluation of all urban sustainability strategies, recognizing that there are many different and sometimes competing goals related to urban sustainability.
