By Kate Gallego, Mayor of Phoenix, Arizona

Phoenix is the fifth-largest and fastest-growing big city in the US, with an ambitious vision to become the most sustainable desert city on the planet. Located in the heart of the Sonoran Desert, heat is a fact of life for Phoenicians – people are more likely to carry gloves to protect their hands from hot steering wheels in the summer than cold in the winter. A balance between the sometimes competing priorities of cooling solutions and water conservation necessitates a unique and innovative framework of heat response and mitigation strategies.

Though the Valley of the Sun has been inhabited for millennia, climate change has exacerbated summer heat extremes. The impacts of increasing temperatures on public health and quality of life are, in turn, exacerbated by urban development patterns and compounding risk factors. Protecting the quality of life of Phoenicians requires a robust public health approach, as well as creative deployment of cooling strategies to improve our built environment. That’s why I led the creation of the City of Phoenix Office of Heat Response and Mitigation, the first publicly funded heat office in the country, to ensure a full-time focus on heat issues and coordination inter-departmentally and with community stakeholders.

A comprehensive approach demands strategies for immediate extreme heat response to protect our most vulnerable residents, mid-long-term strategies to make our communities cooler, and strategies to reduce our impact on the climate by pursuing net-zero emissions.

Extreme heat response

Mortality from environmental heat is a significant challenge in Maricopa County, home to Phoenix. The county government, which serves as the local public health authority, shares data that reflects the complexity of addressing the threat of extreme heat, with housing insecurity and behavioral health challenges as significant risk factors. In 2021, there were 339 heat-associated deaths in Maricopa County, 178 of which occurred in Phoenix. This was a 5% increase from 2020 and a 70% increase from 2019. Sixty percent of these deaths involved substance use, with 48% involving methamphetamine. Homelessness was a factor in 38% of all heat-associated deaths. The racial disparities are also notable. African American and American Indian residents had the highest heat-associated death rates per 100,000 people. Heat disproportionately impacts populations and communities that already face the most risk factors.

Heat causes more deaths each year than most other natural hazards combined, yet the national emergency planning and response mechanisms lack the same resources that are dedicated to other types of extreme weather events. Under the US Federal Emergency Management Agency’s (FEMA) disaster declaration mechanism, heat is not included among the 16 incident types delineated where there are six different categories for storm severity alone. The metrics of what is considered “extreme” heat must be locally relevant. The NWS HeatRisk evaluation system could serve as a template for standardization for the activation of additional federal resources. This framework, which is already used operationally in Phoenix and the western US, rates heat event severity by the public health risk to populations of different vulnerability levels. An Excessive Heat Watch or Excessive Heat Warning is issued when level three or four conditions are forecast.      

Figure National Weather Service

Figure 1: National Weather Service      

Strengthening our collective community resources is crucial to reducing the public health impacts of extreme heat. Phoenix is a significant contributor to the regional Heat Relief Network, made up of public, non-profit, and private facilities, which serve as cooling centers that offer water and air conditioning. Cities across the country need more support to grow their ability to meet residents’ cooling and safety needs. The FEMA Hazard Mitigation Assistance Grant and Building Resilient Infrastructure in Communities programs are good starts to building proactive heat response practices, with a focus on improvements such as energy redundancy for cooling centers. Still, with compounding risk factors, additional wrap-around support and personnel are needed during extreme heat events. This could come in the form of additional pop-up shelters and personnel to conduct outreach to individuals who are homebound, facing behavioral health challenges, or experiencing other vulnerabilities. I would like to see the federal government recognize heat as a disaster and allocate more resources for both response and prevention.

Cooling our communities

While I would like to see the federal government do more, I also recognize the important role that cities can play. Cities have been developing heat mitigation strategies to create cooler communities through tree planting, material technology solutions, and building orientation and design, and there remains enormous potential to explore.

Tree planting is the most common strategy deployed by cities to cool streetscapes and improve walkability. In Phoenix, we use a data-driven approach to maximize impact and prioritize equity. We were the first city in the country to take the American Forests’ Tree Equity Pledge, and we are working to ensure that each of Phoenix’s neighborhoods can reach a minimum standard of tree canopy cover by 2030, as defined by each Census tract’s Tree Equity score. Alongside this data, public right-of-way planting locations are prioritized based on their proximity to public transit and key amenities including schools, libraries, and hospitals. To foster safety and walkability, Phoenix has a vision to implement a city-wide network of 100 Cool Corridors by 2030. Planted along pedestrian and transit-oriented pathways, each corridor will include approximately 200 trees, complemented by other heat mitigation and heat-protective strategies like engineered shade structures and drinking water stations.

By necessity and engrained in our culture, Phoenix is intentional about planting native and desert-adapted species. Green Stormwater Infrastructure (GSI), such as vegetated swales and curb cuts, reduces irrigation demands and has co-benefits that include filtering pollutants from stormwater and reducing pressure on traditional stormwater infrastructure. To further support tree survivability, Phoenix established a “tall pot” tree nursery, in which saplings are grown in tubes to encourage growth of a long taproot, so they can survive on natural rainfall alone. Development patterns are fostering denser, more shaded neighborhoods. Zoning codes promote tree planting, including a requirement that all new sidewalks be 75% shaded in the urban core.

Phoenicians are passionate about urban greening initiatives, and residential tree planting is an important tool for increasing energy efficiency, cutting utility costs, and improving walkability. Phoenix is developing a Residential Tree Equity Accelerator to plant 20,000 trees across 25 neighborhoods by 2030. Community organizations are contracted to work directly with residents to ensure proper maintenance, and a resident in each neighborhood will serve as the tree care lead and receive an annual stipend.

Beyond natural cooling mechanisms, technological solutions and smarter design are key. Inspired by the application of pavement sealant in Los Angeles, California, Phoenix developed a Cool Pavement program. The sealant achieves lower surface temperatures through its lighter color and reflectivity, with notable reductions in nighttime surface temperatures. At more than 80 miles of residential streets, the program is one of the largest in the world and is showing potential for an additional benefit – improving the longevity of the underlying pavement.

Southwestern architecture has long reduced the impact of sun exposure on southern and western facing walls and windows. Examples of continued improvement in building design can be found throughout the city. A newly built terminal at Phoenix Sky Harbor Airport has 14,000 square feet of “smart windows,” with glass covered in electrochromic glazing that automatically adjusts tint levels based on cloud cover. Similarly, Phoenix’s central library employs an artful facade design that blocks direct light, controls glare, and improves energy efficiency. The facades feature a custom louver system and shade sails sculpted in Teflon fabric, providing views of the cityscape while diffusing light uniformly.

Smart design must be incorporated across the city, and the benefits should be felt equitably. The Edison Eastlake neighborhood is culturally significant to the African American community and the Civil Rights movement and is home to the largest public housing community in Arizona. Historical underinvestment led to the neighborhood becoming one of the hottest in the county. Supported by a Choice Neighborhoods Grant from the US Department of Housing and Urban Development, the project is transforming 557 outdated units into a mixed-income community of more than 1,000 new homes. Collaboration with residents resulted in a strategy that prioritizes reducing the urban heat island effect and fosters community connectivity to build resilience. Maximization of shade, ventilation, and cool building materials is consistent throughout. Backup water supply and generators bolster resilience during extreme heat events, and community meeting places are designed in each block.

These strategies contribute to the culminating vision of transforming our communities to be in better harmony with the desert environment. We will continue to develop solutions for healthier and more enjoyable communities through collaboration across sectors and all levels of government. Though we face significant challenges, the solutions we are developing can serve as models of resilience and innovation. I’m proud to be leading Phoenix into a future that’s adaptive, equitable, and thriving – and we’re only getting started.

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This article was written for Perry World House’s 2023 Global Shifts Colloquium, ‘Living with Extreme Heat: Our Shared Future,’ and made possible in part by a grant from the Carnegie Corporation of New York. The views expressed are solely the author’s and do not reflect those of Perry World House, the University of Pennsylvania, or the Carnegie Corporation of New York.