The Site Analysis: Heat

Phoenix is a BWh subtropical desert KöppenGeiger Climate Zone. It receives substantial solar radiation throughout the day, and there is not much moisture in the atmosphere to hold the temperature steady, therefore the region experiences dramatic diurnal swings over the course of the day. Temperatures are pleasant in the shoulder seasons, and summer nights and early mornings. However, thermal stress is extremely high between the hours of 8AM and 8PM during the summer months

Phoenix is America’s hottest city. In 2022 alone, there were 378 heat-related deaths in Maricopa County. Most of these deaths occurred outdoors (89%), suggesting a lack of cooling outdoor infrastructure, and most of the victims were older adults (62%), indicating that cooling infrastructure is most critical in areas where there are higher concentrations of vulnerable older residents. Phoenix has made efforts to address the public health impacts of heat by offering and advertising cooling centers where residents can access air conditioning and water on hot days. The City also recently created a designated Office of Heat Response and Mitigation. The office has set a number of goals to mitigate heat through interventions in the built environment, including planting trees along streetscapes and within parks and replacing dark pavement and roofs with more reflective materials.

According to a growing body of literature and the City of Phoenix’s Climate Action Plan, one of the most efficient and high impact solution to provide cooling and other quality of life improvements is to invest in Phoenix’s urban forest. Trees provide cooling effects not only through shade, but also through a process called evapotranspiration, through which they add moisture to the air. Trees can improve air quality, reduce stormwater runoff, increase mental and physical health by improving the quality of outdoor spaces, and raise property values. Per the City’s Tree and Shade Master Plan, the State of Arizona sees a 2.23 to 1 return on investment for every tree planted. Notably, the Inner Loop has some of the lowest tree canopy coverage in the City of Phoenix, ranging from just one to nine percent. Canopy coverage is much lower in the southern half of the Loop than the north, where the Grand Arts District, Capitol Mall, and Garfield and Roosevelt neighborhoods are.