Like Living Things: How Cities Use Energy to Regulate Temperature – Just Like Mammals

Humans, like all mammals, expend energy to keep their internal temperatures within a healthy range. Modern human cities – because we built them that way – do the same thing.

A study published Friday in the journal PLOS Climate takes a new look at how household energy use changes with rising temperatures, applying a model traditionally used for studying animals.

For urban planners, energy companies and emergency managers, the work has implications for energy grid security, cost predictions, and saving lives from heat waves. And for the University of Arizona senior who is the study's lead author, the project is the culmination of her undergraduate career and a steppingstone on her path to helping communities become more resilient to environmental change.

An “Itch to Do Research”

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Halley Hughes, a research assistant in the Bridging Biodiversity and Conservation Science (BBCS) program at the Arizona Institute for Resilience, or AIR, began her project in 2020 amid pandemic lockdowns.

“We had just been sent home,” she said. “It was the heart of COVID, and I was bored.” For a creative, active, and community-oriented young woman, boredom didn’t sit well. She needed a diversion, she said, and “I was getting that itch to do research.”

While perusing emails from her advisor, one message caught her eye. It described a research opportunity studying the links between climate change and heat stress in urban areas. “As a third-generation Tucsonan and self-described ‘desert rat’, that was very interesting to me,” Hughes said.

She talked about the project with her lab group, including her mentor Dave Breshears, a Regents Professor in the school of natural resources and the environment, and Joseph Robert “Robbie” Burger, at the time a postdoctoral fellow with BBCS.

Burger had recently attended a conference where he had learned something new. A biologist at Michigan State University, Richard Hill, had applied a mathematical model developed for studying how mammals regulate their body temperatures to an entirely new area: investigating how human infrastructures use energy in the same way to regulate internal temperatures in cold climates.

The approach treats buildings, and on a larger scale, cities, as if they are living things, Hughes explained. In a way, she added, it makes sense: “Humans made buildings, and we use buildings to maintain a normal temperature for us. To do that, the buildings use external energy in the form of fossil fuels, or if you’re lucky, alternative energy sources.”

The UArizona team decided to extend Hill’s work to investigate energy use in areas stressed by heat, and Hughes took the lead. “Dr. Hill looked at cold places,” she said. “We looked at all of Arizona, which includes cities that can get as hot as 120 degrees.” 

The “Benefit of Our Differences”

Hughes used entirely publicly accessible data from ten large energy companies in Arizona, available at federal or university sources, which showed the energy usage of a large majority of the population of Arizona.

The study is the first to extend Dr. Hill’s work using a biological model to study urban impacts of temperature change, and the first to apply the model to look at the effects of heat. The results demonstrate that merging science disciplines to study urban energy consumption can give urban planners effective tools to prepare for high temperatures.

And because she used open access data from a national dataset, anyone, anywhere can repeat or replicate the study, meaning that the research could be applied to any region nationwide for as many years as data exists.

Hughes also compared per capita income from census data to her map of energy use, and found that in lower income neighborhoods, there were indications of energy insecurity. “In these places people likely are delaying turning on their energy to save money,” she said, “which could be increasingly dangerous if energy costs and temperatures continue to rise.”

Contributing author Ladd Keith, UArizona Assistant Professor of planning and sustainable built environments in the College of Architecture, Planning and Landscape Architecture and a faculty research associate at the Udall Center for Studies in Public Policy, agreed: “This study provides important context for heat planning and governance as heat risk in our communities continues to increase due to climate change.”

Hughes is especially interested in exploring how urban managers can strategize to keep everyone safe with the energy resources available, and in providing individuals and families with the information they need to have autonomy over their energy decisions. “These cities are getting hotter. These people are going to need to cool their buildings to stay safe,” she stated.

A key benefit of this work is that it can be used to predict future energy needs, Hughes added. For example, if the energy use for an area is known for a certain temperature, the information can be used to predict the energy needed to cool the same space when it’s even hotter.

For energy companies, she explained, knowing energy needs of a service area in advance could help prevent events such as rolling blackouts. “The general pattern documented here and its match to the more general theory is really exciting and powerful to see,” Breshears said. 

In addition to Hughes, Breshears, Burger, and Keith, Kimberly Cook, a library and information scientist and doctoral candidate in the University of Kentucky’s Department of Biology, contributed to the paper.

“Interdisciplinary work in research is so critical to providing really insightful and useful results,” Hughes said, noting that she appreciated how the authors applied their diverse expertise to interpreting the results of her study. “All these different interpretations helped us understand more about the data. It was a huge benefit of our differences.”

And “You Can Author a Paper, Too”

Hughes is a graduating honors senior this year, with a double major in global change ecology and urban and regional development in the College of Agriculture and Life Sciences, CALS. Her honors thesis investigates impacts of heat on energy use in manufactured homes in Tucson.

She hopes her own experience in research and early publication can help inspire other undergraduate students to get involved in science as well. “Undergraduates should not be intimidated by research,” she said. “It’s an empowering process, and there are so many opportunities at UArizona to be involved in science.”

To her fellow undergraduates, she would like to say: “Don’t hesitate starting research just because you’re an undergrad. You can author a paper, too!” The UArizona Undergraduate Research Task Force aims to connect all university students with diverse research opportunities.

In addition to her love of science, Hughes also is passionate about science communication, an interest she furthers as a Liverman Scholar with AIR’s Education Initiatives and as an award-winning Planet Forward Correspondent. She is co-director of UArizona’s Students for Sustainability, and an advisory team member for the university’s new Sustainability and Climate Action Plan.

"Halley's work is a perfect example of how our resilience initiatives in AIR aim to combine education, research, and impact," said Kevin Bonine, Director for AIR's Education Initiatives program. "The internships and scholarships provided by our program empower students with real-world experiences, teaching them the ways in which they can make meaningful change in their communities and across the globe through science and environmental communication." 

Following her graduation in May, Hughes plans to pursue a master’s degree in communication and community innovation at CALS. “And then,” she said, “I’ll be fully weaponized in science and communication, and ready to take on the world!”