How Phoenix Reduced Extreme Heat Mortality

In January, the Community Data Health Initiative (CDHI) held a virtual quarterly call of its Extreme Heat Learning Cohort, convening teams from Atlanta, Austin, Baltimore, Chicago, New Orleans, and New York City. The purpose of the cohort is to facilitate peer exchange, partnerships, and equip cities with practical tools for taking on environmental challenges – in this case, extreme heat. 

January’s session featured Dr. David Hondula, the director of the city of Phoenix Office of Heat Response and Mitigation, who presented Phoenix’s data-driven approach to reducing extreme heat deaths, which they have accomplished for two straight years. Hondula shared the data and operational decisions that led to this success, while also naming several deeper governance challenges and questions that remain. 

Below are the key takeaways and lessons from Hondula’s presentation on combatting extreme heat in Phoenix: 

Different heat indicators tell different stories; it’s up to leaders to decide which ones inform policy

After nearly a decade of rising heat-related deaths between 2014 and 2023, Maricopa County has seen a decline over the past two years. Phoenix, which accounts for roughly one-third of the county’s population, has been central to that shift. However, Hondula acknowledged Phoenix still has room for improvement to identify all heat-related deaths in the city. 

“We know that [Maricopa County Department of Public Health] does a really good job detecting heat cases,” he said. “The county’s direct surveillance program catches in the ballpark of half of the excess mortality related to heat,” noticeably larger than the national level, which is “more like 1% to 10%, depending on whose numbers you believe,” explained Hondula.

Hondula explained that his office is currently working in “a data-rich environment,” which has led to helpful insights but also more questions. 

In Phoenix, there are three datasets that tell dissonant heat health stories in the last year – heat-related deaths decreased by approximately 30%, heat-related 9-1-1 calls increased approximately 30%, and calls indicated as heat-related by emergency dispatchers decreased 25-30%. “So, the dispatcher is coding fewer calls related to heat, the paramedics are saying more are related to heat, and fewer people seem to be dying from heat,” said Hondula. “What the underlying narrative behind all of that is – I do not know yet, but we need to figure it out.”

Even with strong local surveillance systems, municipal experts are only able to capture a partial understanding of extreme heat burden on their communities. As a result, city leaders should capitalize on the extreme heat information they do have, and determine which is most vital in making policy decisions – while remaining cognizant of any community impacts that might not be obvious from available data sources.

Heat mortality is highly concentrated, therefore targeted investment can dramatically reduce deaths

In Maricopa County’s annual heat reports, approximately half (48%) of heat-related deaths are among unsheltered residents, who make up less than 1% of Maricopa County’ population, indicating a clear disproportionality. The unsheltered population is at 400 to 500 times higher risk of heat-related death than the general population, explained Hondula. 

Furthermore, a very high percentage of heat-related impacts affect low-income populations, despite media coverage of heat issues highlighting recreational cases such as a helicopter rescue from a hiking trail. If half of heat-related deaths occur among unsheltered communities, the targeting decisions become very clear, explained Hondula.

“Any investment that addresses any part of homelessness and heat is going to pay off big time,” said Hondula. 

Thoughtful operational decisions play a critical role in preventing heat deaths

Regarding definite successes in Phoenix, Hondula highlighted an immediate action the Phoenix Fire Department and paramedics have deployed in recent years on heat-related emergency calls: cold water immersion therapy with ice to lower heat stroke victims’ body temperatures in minutes en route to the hospital. The intervention is relatively low cost, despite being logistically challenging. However, the benefits far outweigh the challenges. 

“The probability that the deployment of this therapy is going to make a huge difference in terms of death or permanent disability avoided – it's almost a guarantee that if this is deployed, it’s going to make a huge difference,” said Hondula of weighing the costs and benefits of the intervention.

Hondula also underscored the importance of extended hours and overnight heat mitigation locations. “Heat doesn't turn off at the end of business hours, and the heat doesn't turn off on Sundays,” said Hondula. Two years ago, the municipal government decided to tackle this issue and opened a 24/7 site and several extended-hour locations at public libraries until 10 p.m. from May 1st through September 30th. The city also demonstrated agility in its new approach when unprecedented late season heat motivated extending heat relief operations into October in 2024. 

While staffing the overnight and extended hours sites with volunteers, mental and behavioral health specialists, public health teams, and security cost the city approximately $4 to $4.5 million, the effort was unquestionably worth it, according to Hondula and his colleagues, when considering the number of lives impacted and potentially saved. 

How city systems operate during extreme heat events can be as consequential as city infrastructure itself. The staffing and coordination of both resources and manpower can have an incredibly high impact as seen in these examples from Phoenix.

Cities lack a clear framework to weigh the benefits of heat interventions, particularly for long-term prevention

Despite its clear successes, Hondula pointed out that in Phoenix, like in many cities, there is currently no definitive formula that points to the maximal return on investment to addressing extreme heat in cities, particularly for preventive and upstream interventions. “I think it's so hard because of the multifaceted nature of heat and how there is a range of solutions from super upstream to super immediate,” said Hondula.

At the moment, officials cannot yet assess the total “value” of programs like weatherization (i.e. improvements to buildings and city infrastructure to reduce energy consumption, lower utility costs, and increase comfort) or long-term benefits of those investments – and perhaps may be undervaluing it – from the heat health data currently available to them. Ongoing open-ended questions experts and city officials are hoping to answer include: What can be gleaned from the cumulative impacts of sustained high-heat days? How should cities allocate investments based on need?

If cities want to quantify the full impact of heat interventions, officials cannot solely look at data regarding heat-related illness and deaths. There is plenty of opportunity in other types of data to holistically understand the impact of heat, including measures reflective of quality of life, chronic health conditions, learning, work productively, and more, explained Hondula.

Phoenix’s reduction in heat-related deaths over the last two years demonstrates exciting progress that deserves to be celebrated. Yet, even in one of the most “data-rich environments” in the country, questions remain on how to further improve detection and best utilize insights from the data collected. 

The ultimate lesson from Hondula’s presentation: it’s not about following a specific playbook as “success” cannot be defined by one data point. Rather, progress requires continuous iteration on what data is being evaluated, what insights from the data are being elevated, how those insights inform operational decisions, and being responsive as new information emerges.