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Neighborhood Ecosystems: Human-Climate Interactions in a Desert Metropolis

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Neighborhood Ecosystems is an interdisciplinary study of the impact of urbanization on human-ecological-climate interactions. The site for the study is Phoenix, AZ, a rapidly growing metropolitan region that is steadily converting agricultural and desert land into residential neighborhoods.

Exposure to excessively warm weather is a significant threat to human health and well-being in cities around the world. The process of urbanization is strongly linked to increasing temperature through the formation of heat islands, and these local effects are likely to intensify with future trends in global warming.

The neglect of poor inner-city neighborhoods and construction of new large-scale middle class housing developments on the urban fringe intensify and enlarge the urban heat island through the replacement of vegetation with impervious surfaces and heavy traffic. The inequalities in biophysical environments between more affluent, predominately white neighborhoods and lower- to middle-income neighborhoods continue to put economically and socially marginal populations at a higher risk of exposure to excessive heat and all that it entails.

Social, ecological and climate changes are likely to continue in the future in some of the world’s fastest-growing metropolises, which are located in arid and semi-arid regions. Arid cities face unique environmental challenges that accompany population growth, including extreme heat, limited water resources and shade, and harsh conditions for species survival.

Neighborhood Ecosystems is an interdisciplinary study of the impact of urbanization on human-ecological-climate interactions. The site for the study is Phoenix, AZ, a rapidly growing metropolitan region that is steadily converting agricultural and desert land into residential neighborhoods. In this study, we integrated theory, research questions, and data from sociology, geography, ecology, geological sciences, and urban planning at the neighborhood scale in order to study the organization of human activity, ecological services, and microclimates.

Neighborhoods are inter-connected, socioecological systems that bridge elemental social and ecological patterns and processes with larger scale social and biophysical phenomena. Specifically, we related the social and economic characteristics of human settlement patterns to the spatial distribution of environmental resources (vegetation, climate) across the urban landscape. We examined the vulnerability of human populations in different neighborhoods to a major climate-related stressor, the urban heat island.

Data were collected regionally in census tract units (approximately 1 square mile) over an area of approximately 925 square miles, as well as for eight neighborhoods defined by census block groups, which are smaller and more homogeneous areas than tracts. Regionally we combined remotely sensed satellite imagery (vegetation abundance and surface temperature), U.S. Census (population characteristics), and a digital elevation model of the region’s topography. For eight neighborhoods, in addition to scaling the regional data down to block group boundaries, we also collected data on housing quality and water consumption for a sample of households, acquired land use classifications, and monitored the neighborhood microclimates using portable air temperature/dew point loggers for 12 consecutive months. Data were analyzed using GIS mapping software, statistical procedures, in-depth qualitative analysis of the sites and a computer simulation model of human thermal comfort (OUTCOMES – OUTdoor COMfort Expert System, Heisler and Wang, 2002).

Major findings:

  1. Human settlement alters the urban climate and spatial differences in temperature can be detected at the local or neighborhood scale.
  2. The distribution of vegetation density is a key mediating variable between human decision-making and the regulation of microclimates, which is an important ecosystem service.
  3. Data from high spatial resolution airborne sensors, and high temporal resolution satellite sensors that are now available will help to resolve further the historical and current complexities of social/biophysical interactions that produce variability in the urban heat island.
  4. Residential landscaping constitutes a large proportion of the urban land cover, yet an understanding of the motivation for landscaping preferences and behaviors is only beginning to emerge.
  5. Feedbacks from neighborhood microclimates to human residents include exposure to extreme summer heat, especially during periods of heat waves.
Harlan, S. L., Brazel, A. J., Jenerette, G. D., Jones, N. S., Larsen, L., Prashad, L. & Stefanov, W. L. (2008). In the shade of affluence: The inequitable distribution of the urban heat island.Research in Social Problems and Public Policy, 15, 173-202.

Jenerette, G. D., Harlan, S. L., Brazel, A., Jones, N., Larsen, L. & Stefanov, W. L. (2007). Regional relationships between surface temperature, vegetation, and human settlement in a rapidly urbanizing ecosystem.Landscape Ecology, 22, 353-365.

Harlan, S. L., Brazel, A. J., Prashad, L., Stefanov, W. L., & Larsen, L. (2006). Neighborhood microclimates and vulnerability to heat stress.Social Science & Medicine, 63(11), 2847-2863.

Larsen, L. & Harlan, S. L. (2006). Desert dreamscapes: Residential landscape preference and behavior.Landscape and Urban Planning, 78, 85-100.

Stefanov, W. L., Prashad, L., Eisinger, C., Brazel, A. & Harlan, S. L. (2004). Investigation of human modifications of landscape and climate in the Phoenix, Arizona metropolitan area using MASTER data. The International Archives of the Photogrammetry, Remote Sensing, and Spatial Information Sciences, 35(B7), 1339-1347.

Brazel, A. J. &  Crewe, K. (2002). Preliminary test of a surface heat island model (SHIM) and implications for a desert urban environment, Phoenix, AZ.Journal of the Arizona-Nevada Academy of Sciences, 34(2), 98-105.

Funding Sources: 
National Science Foundation Grant No. SES-0216281
Biocomplexity in the Environment, Coupled Human and Natural Systems

Sharon Harlan, Arizona State University School of Human Evolution and Social Change, Principal Investigator
Anthony Brazel, Arizona State University School of Geographical Sciences and Urban Planning, Co-Principal Investigator
Larissa Larsen, Co-Principal Investigator
William Stevano, Co-Principal Investigator
Nancy Jones, Research Assistant & IGERT Fellow
Lela Prashad, Research Assistant & IGERT Fellow
Chris Eisinger, IGERT Fellow
Sara Grineski, IGERT Fellow
Brent Hedquist, IGERT Fellow
Darrel Jenerette, University of California, Riverside, IGERT Fellow
Matthew Alan Lord, IGERT Fellow
John Parker, IGERT Fellow