Sensing heat: How scientists in Phoenix study summer's deadliest invisible threat

Against the beginnings of a vermillion sunset made more stunning by heat-enhanced air pollution scattering less-vibrant wavelengths, researchers from the Southwest Integrated Field Laboratory set up for an evening of public education at Phoenix's Desert Botanical Garden.

Peter Price, a Ph.D student in Arizona State University's Herberger Institute design school, bends his tall frame to pull the little red wagon housing "MaRTy2," one of the team's two smaller mobile weather monitoring units, across gravel at sunset plaza, the garden's designated stage for each day's costume change to night.

Elevated to approximately head-height in the wagon, MaRTy2's instruments can measure and record location-specific air temperature, humidity and wind speed, as well as solar radiation (visible sunlight and UV rays) and longwave radiation (heat emitted from surfaces). The last two values are less typical for weather equipment and are what make the two "MaRTy" carts special, Price says. They can be combined to produce an estimate of the mean radiant temperature (MRT) that would be experienced from above and below by a pedestrian in that spot.

When not wheeled out for public display or data collection, MaRTy1 and MaRTy2 live in the SHaDE Lab at ASU, an urban climate research group directed by Ariane Middel that stands for Sensable Heatscapes and Digital Environments. Situated within the School of Arts, Media and Engineering and the School of Computing and Augmented Intelligence, the initiative represents an interdisciplinary convergence of different research approaches onto one of the state's most pressing of problems, what Middel calls "the 'hot' topic of urban heat."

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Heat in Phoenix is both sensable, as in possible to sense (some might call it impossible not to sense), and sensible as an area of study. Last year, record-breaking temperatures contributed to the heat-related deaths of 645 people across Maricopa County, a 52% increase over the 425 who succumbed to heat the previous year. This escalating death toll is despite an increase in efforts by many groups to provide water, cooled shelter and other services throughout the summer.

On a call with reporters last month, Michelle Litwin, Phoenix's Heat Response Program manager, said her team handed out 400,000 water bottles and provided 28,000 people with heat response supplies last year in hopes of flipping that trajectory of human loss. The city is also planting more tree shade, testing reflective pavement coatings and operates a "Cool Caller" program to check on vulnerable residents during heat waves.

But it's clear more work is needed to address the soaring impact of intensifying heat.

Centering on the heat problem

In Phoenix's urban environments, data from the National Weather Service show that average July temperatures in the 1920s, when this collection of records began, were between 89.3 and 92.7 degrees. Over the past decade, that average has not dipped below 94.7 and hit a new high of 102.7 degrees in 2023. Scientists who have compared temperature changes in dense urban areas to those in nearby parks, forests and farmlands say the increase is about half due to human-caused climate change and half due to the heat-trapping result of development sprawling out in every direction.

An analysis published Wednesday by the nonpartisan research organization Climate Central zoomed in on this urban heat island (UHI) effect in 65 major U.S. cities to explore the inequity of warming across urban areas. Their map of calculated UHI values across census block groups in Phoenix shows a pattern of greater temperature increases in lower-income and minority neighborhoods as a result of zoning and development that incorporated less cooling vegetation or heat-aware urban planning. Consequences are often higher heat-related death tolls and costs of staying alive.

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On average, the report determined Phoenix residents experience temperatures that are 7.4 degrees hotter due to urban development, on top of the atmospheric warming caused primarily by burning fossil fuels. In Tucson, the urban environment has resulted in temperatures that are 7.7 degrees higher on average.

These are actually some of the lowest average increases reported out of 65 cities analyzed, which Climate Central's senior data analyst Jennifer Brady said can be explained by the more diffuse impact of Arizona's sprawling development style compared to more compact cities with denser downtown areas. Regardless, since Arizonans already exist at the edge of survivable summer temperatures, any extra warming can become an existential threat.

"This is 'additional heat,'" Brady said. "An additional 7 or 8 degrees (in Phoenix) is going to, on average, be added to a much higher baseline temperature than in some place like New York, which had neighborhoods with higher UHIs."

While science is always bolstered by similar results confirming known patterns, none of this is news to scientists and leaders based in Phoenix where, as a matter of necessity, some of the most groundbreaking heat studies and mitigation efforts are already taking place.

Phoenix is paving the way on urban heat research and mitigation

Represented at the Desert Botanical Garden's sunset plaza by just a fraction of its members, the scientists of the Southwest Integrated Field Laboratory, or SW-IFL, hail from all three Arizona state universities plus the Brookhaven National Laboratory, the Oak Ridge National Laboratory and IBM Research. In recognition of the modern severity of urban temperatures, they've teamed up to study the ways heat in cities can be sensed by instrumentation, experienced by humans and modeled using simulations.

The end goal is to deliver "next-generation" predictive tools and resilient solutions that are both specific to the Southwest and translatable across the sunbelt.

Read our heat + housing series:As Arizona builds to solve a housing crisis, will its homes withstand future heat extremes?

SW-IFL's mission is one example among many of how Phoenix researchers are paving the way — in this case by studying pavement — for other cities sure to be confronted with unprecedented heat extremes as climate change and urban development continue to progress.

Other Phoenix-based heat laboratories include a branch of the national Center for Heat Resilient Communities, which was recently awarded $2.25 million in federal funds from President Joe Biden's Inflation Reduction Act and is led locally by ASU professor Sara Meerow, also a scientist with SW-IFL. Another is the Southwest Sustainability Innovation Engine, a collection of research institutions, cities and business partners led by ASU that was launched in January with $15 million from Biden's CHIPS and Science Act to "deploy new solutions to extreme regional dryness and heat." Beyond those initiatives, ASU's Global Futures Laboratory hosts more researchers focused on urban heat than you can shake a rain stick at.

Across the state, quick scans of the University of Arizona's Extreme Heat Network, professor Ladd Keith's work with UA's Climate Assessment for the Southwest, or climate modeling by Northern Arizona University's Ecological and Environmental Informatics group and United Nations climate report author Kevin Gurney show the local depth of knowledge on rising temperatures. Arizona-based scientists with the Grand Canyon Monitoring and Research Center, the Southwest Biological Science Center and the National Ecological Observatory Network, to name just a few, add to the state's expertise.

Phoenix's municipal leaders are also increasingly seen as experts on heat and how to deal with it.

The stampede of national and international news outlets that have looked to former ASU heat researcher David Hondula for comment on how cities can manage the risks of unexpected heat waves since he took the helm at Phoenix's Office of Heat Response and Mitigation indicates the authority Arizonans have established on understanding urban heat.

Phoenix Mayor Kate Gallego was also tapped innumerable times during last summer's record-breaking heat to weigh in on how cities less familiar with high temperatures can attempt to prepare. Despite being frustrated at many of the resulting news stories labeling Phoenix an "inferno," a "hell on earth" or "a blighted dystopian hellscape," she remains positive that America's hottest big city can still become the world's most sustainable desert city, a central part of her platform as a politician and former environmental studies major.

The Mayor responds to heat in the news:Mayor Kate Gallego on Phoenix's 'hellscape' year and what's in store for 2024

Gallego has taken steps toward this desert sustainability goal by creating the nation's first publicly-funded heat office, now run by Hondula, passing a Climate Action Plan to track and reduce the city's greenhouse gas emissions, pushing for more electric vehicle infrastructure, launching a pilot program for cool pavement coatings and securing federal funding for more tree shade, among other initiatives.

But she has also taken heat for allowing unsustainable growth (her office is currently considering streamlining building permit approvals), including welcoming an influx of data and microchip technology centers into the region that require huge amounts of energy and manufacture more heat and emissions.

Cooling pavement initiative needs to heat back up

At the same time that Phoenix-based heat initiatives establish expertise, solutions missteps also serve as lessons.

One of those might be Gallego's faltering cool pavement program. In a video about the 2021 pilot study for the program, ASU heat researchers Jennifer Vanos and Ariane Middel shared mostly positive results about the potential for light-colored pavement coatings to reduce temperatures on city streets and in neighborhoods. There are some reflectivity issues that could expose pedestrians to higher temperatures in some cases (as measured by head-height MaRTy carts). But overall, they concluded the option seems promising, with average afternoon surface temperatures on treated streets 10 to 12 degrees lower than traditional dark asphalt.

This could be life-saving for lower-income or unhoused Phoenix residents who spend more time waiting for buses or walking to destinations, said David Sailor, who leads the SW-IFL team as another member of ASU's urban heat research professoriate and works with the city to study cool pavement applications.

"We have a lot of pedestrian deaths in Phoenix and Tucson, it's really bad," he said. "The cooler pavement surface might also improve visibility at night."

Given these results, Sailor is not sure why the city hasn't applied more of the cooling sealant. The Phoenix Street Transportation Department's cool pavement website shows that about half of the districts slated for treatment in 2023 were rescheduled for 2024.

In response to The Republic's inquiries about this, Sasha Perez, a spokesperson for the street department, said in late June that since 2020 the city has completed "120.4 total miles of cool pavement installation to date." That's the same number listed on tallies posted to the program website as of August 2023. She said the application schedule for 2024 is set to resume later this year after the department completes "its testing of materials to evaluate product specifics and ensure performance standards are met."

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Sailor had a more grim take, noting that streets have to be resealed every few years anyway and the cost difference is minimal between the traditional dark sealant and the promising cooling sealant. (The reporter's own residential street in Phoenix received a fresh coat of dark sealant earlier this year.)

"Street departments that have been doing things a certain way for 30 years are not incentivized to do something different," Sailor said.

Gallego did not respond to questions about why the program has fallen behind schedule, but did send a statement reaffirming the benefits of cool pavement and Phoenix's status as a leader on urban cooling strategies.

“Along with increasing shade and encouraging smarter design for our desert climate, cool pavement is an important tool to reduce the impacts of the urban heat island effect," Gallego told The Republic in late June. "Phoenix has the largest cool pavement program in the country, and we continue to analyze its performance over time in partnership with Arizona State University.” 

Sense and sensability

While city employees become the first to navigate the logistics of many heat mitigation options, researchers in Phoenix press on to collect the data necessary to drive these efforts.

Parked on the other side of the sunset theater from where Price pulls the MaRTy cart, another heat-sensing vehicle appears to be a scaled-up version of the same. For the moment, the Brookhaven National Laboratory's Center for Multiscale Applied Sensing is headquartered in a Ford F550 truck with a bed full of specialized monitoring equipment designed to capture even more detail about the atmospheric signatures of heat waves.

The center's environmental and climate scientists, including director Katia Lamer, often travel with it from New York, chasing heat waves. After stopping at the public engagement event at the Desert Botanical Garden, she and her crew planned to drive the truck through neighborhoods in Phoenix, Tucson and beyond while its instruments record a deluge of data about how complex urban environments influence sensed heat.

Lamer says the truck's mobility adds granularity to the scientific understanding of fine-scale temperature differences across space. The team also returns to certain areas to monitor changes over time as the human forces of development and climatic warming extend their reach.

"We use a combination of remote sensors that emit light and wait for it to be scattered by aerosols or clouds to measure wind patterns, the thickness of clouds overhead, rain when it falls to the ground," Lamer says, listing a few of the truck's capabilities. "We also use weather balloons to take profiles of air temperature and humidity. The idea is that each piece of instrument on board measures a different component of the weather and climate system. And when we put it all together, we can understand how things work."

A saguaro arm's reach away, Alamin Molla, a Ph.D student working with Sailor at ASU, explains to visitors how heat research also involves measuring longwave radiation and radiative flux from helicopters and satellites. He points to different areas on a large printed map that shows a patchwork pattern of sensed heat throughout the Valley.

Some spots on the map are bright red, including downtown Phoenix and South Mountain, where a boy died from heat exposure on July 3. Even though the area the boy was hiking with his family is undeveloped, that south-facing rocky landscape absorbs and retains a lot of heat from the sun, Molla explains.

Other mapped locations appear a relative lush green, including swaths of Scottsdale and Tempe where urban planning and tree planting have been prioritized. Members of the public are encouraged to add a push pin to the map in the area where they live and to engage in discussion about its hue.

Read our climate series:The latest from Joan Meiners at azcentral, a column on climate change

Zooming out, these collective efforts to understand and address heat in Phoenix at different scales and with different tools may very well be unrivaled.

But that seldom seems to factor in to how much heat the city takes as criticism for its extreme summers from people who choose to live elsewhere. Many Valley residents love the heat. Others make seasonal plans to escape it. While old timers debate how much it has increased over time — proclaiming "it has always been hot here" — legions of scientists who have measured this advocate for strategies to control its rise.

Either way, Arizonans are sensing the heat.

Joan Meiners is the climate news and storytelling reporter at The Arizona Republic and azcentral.com. Before becoming a journalist, she completed a doctorate in ecology. Follow Joan on Twitter at @beecycles or email her at joan.meiners@arizonarepublic.com. Read more of her coverage at environment.azcentral.com.

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