As global temperatures continue to rise, cities are increasingly feeling the heat as a result of the Urban Heat Island Effect. No city feels this quite like Phoenix, due to its position in the Sonoran Desert where temperatures in the summer average 40°C, and in 2023 experienced 55 days of 43°C heat in a row. According to NASA, 2023 is the hottest summer in recorded history and is on track to being the hottest recorded year. The effects of climate change are being felt worldwide but due to its geographic placement and urban typology, Phoenix is facing the reality of climate change far faster than other cities. In response, the city is getting creative. In 2021, the city government of Phoenix created the Office of Heat Response and Mitigation, the first of its kind in the world. This publicly funded office focuses both on helping residents cope with hot weather (response) and cooling the city through urban intervention (mitigation).
As climate change continues to worsen and urbanization increases, urban adaptation is necessary to ensure safe and livable cities. The United Nations predicts that by 2050, 7 out of 10 people worldwide will live in cities, so rising temperatures will soon affect more people than ever. Due to its unique geographic location and extreme heat, Phoenix is acting as an unofficial laboratory for climate adaptation that other cities can learn from. So, what is Phoenix doing to mitigate its heat island effect?
Growing 11.2% to 1.6 million inhabitants, Phoenix was the fastest-growing metropolitan area in the United States between 2010 and 2020. With this population growth came the construction of new housing and, in the chronically car-dependent city, parking lots to accommodate new residents. All of this construction combined with the city’s location in the Sonoran desert constrains the possibilities of greenery and green space. Greenery reflects heat and cools the urban environment, while manmade materials absorb heat throughout the day and release it at night.
Average summer temperatures in Phoenix regularly exceed 40ºC, necessitating the use of air conditioning. Rather counterintuitively, air conditioning makes cities hotter. Air conditioning and urban heat are intertwined in a vicious cycle, while air conditioning keeps buildings comfortably cool in the heat, it also transfers heat back outside, further worsening the urban heat island effect.
To increase greenery and thus decrease temperatures, Phoenix’s city government has set goals for all neighborhoods to adapt their landscape. The goal is to have 25% of Phoenix covered by a canopy of native tree species by 2030. As of 2023, the city has achieved 12.4% coverage. Planting more trees is difficult due to the desert environment, as limited plant species can grow in such a harsh environment. Additionally, planting non-native species requires the use of excess water, which is scarce in the desert environment.
In addition to the environmental challenge of tree planting, there is also the consideration that trees cost money and time. In Phoenix, heat disproportionately affects low-income people, for whom planting a tree on their property is not a high priority. Buying and maintaining trees costs money, and a water bill increase is out of reach for some. Hence, wealthier neighborhoods have higher percentages of tree cover and thus lower temperatures. To make tree planting more accessible, the city government has implemented several grant programs to subsidize tree planting around the city. They have also introduced a tree donation program through which individuals and organizations can donate trees to underprivileged neighborhoods. Additionally, community volunteer programs such as Love Your Block and Citizen Forester collaborate with the city to plant trees in low-income neighborhoods.
Arizona State University’s (ASU) SHaDE (Sensible Heatscapes and Digital Environments) Lab is an innovate research program aimed at tackling the question of how to adapt the city to rising temperatures. Using Phoenix as its laboratory, they are designing innovative solutions for heat mitigation.
ASU’s SHaDE Lab has identified one of many potential points of cooling: Phoenix’s streets. As materials such as asphalt absorb heat and make the city hotter, the city has begun experimenting with painting its roads with a light-colored pavement coating that reflects heat. This paint is being piloted in several neighborhoods and has been successful, seeing lower temperatures by 5-6ºC.
Applying the same principles of street painting to buildings is Phoenix’s Cool Roofs Initiative, a pilot program and study aimed at retrofitting existing buildings to mitigate heat absorption and reduce energy consumption. This pilot began in 2013 and painted over 6,500 square meters (70,000 square feet) of roofing, covering roughly 15,000 buildings, or 3.5% of all buildings in Phoenix. The participating buildings saw a 17% reduction in energy consumption and a reduction in roof surface temperature, but unfortunately the Cool Roofs study did not find a significant decrease in neighborhood temperature. However, the study was not concentrated within neighborhoods, measuring participating buildings across the metropolitan area, and did not measure temperature reduction from reduced air conditioning usage. To fully understand the effect of Cool Roofs on temperature, this should be studied within certain neighborhoods where the majority of buildings have Cool Roofs. The widespread implementation of cool roofs and green roofs can be a potential solution.
Due to its geographic position and urban typologies, Phoenix is in urgent need of climate adaptation measures as we enter an unprecedented era of climate change. The city is turning to urban design innovation to curb the effects of its excessive heat. Time will tell if these initiatives will be successful, but early results seem promising. Phoenix is turning to collaboration to solve its climate problems, emphasizing the fact that climate change affects us all, regardless of race or class. By working together, we can adapt our cities to climate change.
