Skip to main content

Project examines urban residents’ vulnerability to heat

October 28, 2008

Sophisticated climate and environmental data will be combined with social science knowledge by a team of Arizona State University researchers investigating human vulnerability to deadly heat exposure. 

With the mounting effects of climate change and half the world’s population now living in urban areas – one-third of the people in slums – the potential for the increasing frequency and severity of heat waves is cause for grave concern, says Sharon Harlan, an associate professor of sociology in ASU’s School of Human Evolution and Social Change in the College of Liberal Arts and Sciences. 

“People in cities are in double jeopardy due to urban heat islands and global climate change – factors that are increasing and intensifying as they interact,” she says. 

Exposure to extreme heat events could lead to even larger disasters than some seen in the recent past, such as the heat wave that took as many as 50,000 lives in Europe in 2003. 

Harlan will lead researchers in seeking answers to guide policymakers and planners in bolstering protective measures to prevent heat-related illness and deaths. The collaborative project, partnering ASU and the University of California, Riverside, is supported by a recently awarded $1.4 million grant from the National Science Foundation. 

The teams will examine how global environmental change combines with local conditions to affect human vulnerability to climate change. Studies show the urban poor are most vulnerable to extreme heat, but little is known about the interplay between changing urban climates and the human and natural systems within cities. 

Studying a desert metropolis 

Metropolitan Phoenix is the ideal living laboratory for the project. It is heavily populated, hot and arid – like many places around the world experiencing rapid urbanization and limited water supplies. 

Over the past 50 years, the Valley’s summer minimum temperatures have increased by an average of more than 10 degrees Fahrenheit due to the urban heat island effect, while the number of daytime hours with temperatures exceeding 100 degrees has increased significantly. Additionally, the metro area’s central corridor contains fairly distinct neighborhoods of ethnic and socioeconomic diversity. 

“At its core, this project is focused on how society impacts and interacts with the environment,” says Chris Martin, a professor of horticulture at ASU’s Polytechnic campus and co-principal investigator for the project. “It’s about understanding the stratification of society along socioeconomic gradients and how that results in environmental stratification.”  

Higher-income areas are usually cooler, and one of the reasons is the increased amount of vegetation, such as lush lawns, that surround homes. This leads to another issue: Vegetation can somewhat diminish the heat island effect, but at the cost of water, a limited resource in the Southwest. 

Darrel Jenerette, a landscape ecologist and project researcher at the University of California, Riverside, says the team’s research will also look at the trade-off between water use and how it affects local climate and spatial components. For example, he says, “How does one tree incrementally affect its immediate environment – a yard, a neighborhood, all the way up to the entire region?” 

Merging disciplines to see the big picture 

More than a dozen researchers working in nearly as many scientific disciplines and subdisciplines are involved in the project. 

Harlan explains: “The equal partnership among the social and natural sciences, mathematics and education will allow us to use sophisticated modeling tools to analyze urban systems while not losing sight of the health and well-being of real people who live, work and go to school in vastly different neighborhoods.” 

Will Stefanov, a senior geoscientist at the Image Science and Analysis Laboratory at NASA’s Johnson Space Center, provides a novel view of the Phoenix-area landscape. “This is an excellent project to use NASA’s Earth remote sensing resources in a very relevant way,” he says. The remotely sensed information is collected from satellites in space or by instruments in airplanes, and “gives you data on the entire city area at one point in time, which can be used to map differences in vegetation, surface temperature and land use and land-cover patterns.” 

Looking at these “snapshots” of the urban area over time, Stefanov says, helps reveal patterns of physical change that influence the development of the Phoenix urban heat island. 

The importance of studying one prototypical metropolis is apparent when considering that global climate changes and growing populations are likely to compound the heat island effect and spur creation of new heat islands around the world. 

Susanne Grossman-Clarke of ASU’s Global Institute of Sustainability will assist in creating a heat profile of Phoenix, and conduct regional atmospheric modeling using the Weather Research and Forecasting model. 

The model calculates – among many other variables that characterize the state of the atmosphere in a region – 2-meter air temperature and humidity with a spatial resolution of approximately one kilometer. 

“That means we will obtain air temperature and humidity predictions for each square kilometer of the Phoenix metropolitan area,” Grossman-Clarke explains. “Regional air temperatures depend on the global climate, which is modified by the interaction of local mountains and land use with atmosphere. Therefore, to assess the air temperatures for our region in the future, we need to understand the interactions of global climate change and ongoing urbanization on the atmosphere.” 

Grossman-Clarke is working closely on this aspect of the research with Joellen Russell, a climate modeler from the University of Arizona, who will select times when the Global Climate Model indicates heat wave conditions over Arizona. The team will use the climate information together with the regional Weather Research and Forecasting model to estimate temperatures under those conditions in a process known as “downscaling.” 

For health-related data, the team will rely on ASU’s Center for Health Information and Research, a part of the School of Computing and Informatics in the Ira A. Fulton School of Engineering. 

“We will be using data from our Arizona HealthQuery (AZHQ) database to identify patients receiving care for heat-related or heat-exacerbated conditions, and we will collaborate with the other researchers to provide this data in an optimal format for their analyses,” says Wade Bannister, the center’s associate director for informatics. “AZHQ is a unique resource for this project because it contains patient-level data across healthcare systems and over time, enabling the researchers to more accurately assess the differences in health effects in specific geographic areas.” 

Ground-breaking research 

A part of NSF’s Dynamics of Coupled Natural and Human Systems Program, the project is one of only 10 chosen this year for funding. “We are in good company with other institutions that are also known for high-quality research on society and environment,” says Linda Lederman, dean of social sciences in ASU’s College of Liberal Arts and Sciences. Designed to produce a new integrated system dynamics model of heat-related health impacts in cities, NSF reviewers indicate the endeavor has the potential to be ground-breaking research. 

Harlan says the modeling team, lead by Tim Lant, research director of ASU’s Decision Theater, will “project alternative future scenarios of heat riskscapes, vulnerability maps and public health outcomes in the face of rapid urbanization. We hope to shift the balance of public relief efforts toward making modifications in the built and social environments of the city rather than simply advising people to stay out of the heat.” 

The team is to share findings locally and nationally with city planners and health agencies and to provide data to public health officials responsible for developing early warning systems and heat-illness prevention programs. The results will also be made known to the community to promote better decision-making. 

Lant believes the study has a practical application in illustrating the “effects of climate change and urbanization on the health of Arizona citizens, and helping us plan our cities for a more sustainable future.” 

The Decision Theater will present the findings on its 260-degree screen and through technology that allows information to be displayed off-site. In addition, participatory research and educational activities for low-income and minority populations will be developed, including the production of a special people and climate edition of the ASU-produced “Chain Reaction” children’s science magazine.