Urban Sprawl: Phoenix

Most people think of urban sprawl as the construction of roads and buildings at a rate that exceeds population growth. Phoenix, Arizona, however, offers a contrasting model of sprawl. Its metropolitan area has grown more than 300 percent in recent decades, but its population has grown even faster. Since the mid-1980s, the city’s population density has increased as people continue to move to the region even as the urban area’s boundaries have grown more slowly. This trend is by necessity, since the water supply cannot feed an ever-expanding metropolitan area.

For Educators 

Exploring In-Depth

Phoenix, Arizona has seen its population increase at a rate greater than that of its urban boundaries. This trend is by necessity, since the water supply cannot feed an ever-expanding metropolitan area.  Provided here are questions that will help guide a discussion about urban sprawl.

  • When you think of urban sprawl, what do you picture?
  • How is urban sprawl in Phoenix different from the typical urban sprawl?
  • How has the invention of the air conditioner affected population growth in Phoenix?
  • The population of Phoenix is increasing, yet the boundaries of the city remain the same. Why is this occurring?
  • What foremost problem does the growing city of Phoenix face?

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Water has always been at the heart of human culture in the region, for it is where the Salt and Gila rivers converge in the Sonoran Desert. This ready supply of water supported the Hohokam culture, which lasted for two millennia. The Hohokam dug canals to channel otherwise scarce water to their crops. The Hohokam were gone by the time Europeans arrived, but canals have remained vital to people in the area. At the opening of the twentieth century, Phoenix had just over 5,000 residents, but aggressive water projects brought more people and more farms to the region. By mid-century, air-conditioning made the climate more bearable, and military bases and military-related industries bolstered the economy.

 As more people moved to Phoenix, demand for water increased, leading to serious problems. By the 1960's, most of the city's water was drawn from the ground, and the surface would sink when the water table dropped too far. The Central Arizona Project (CAP), an aqueduct system that brings water from the Colorado River, was completed in the late 1980's. Initially, most of that water was used by farmers, but more recently, the CAP has been supplying urban areas with growing populations. Today, more than 3.3 million people live in the Phoenix metropolitan area. 

The CAP and other surface water projects have reduced Arizona's dependence on groundwater, but they have not eliminated the problem of groundwater withdrawal. Furthermore, recent droughts have heightened concerns that Phoenix needs more water to sustain its human population. Water conservation will be vital in supplying water to Phoenix's growing population. One study suggested that water conservation, high density "smart growth," and the reduction of outdoor water uses could reduce wasted water by up to 77 percent. Planners in Phoenix and other cities of the arid West welcome numbers like these, for they may mean that cities can grow without using ever more resources.

This visualization uses a combination of map data and satellite imagery to illustrate the rise of modern Phoenix. Phoenix is home to the Central Arizona-Phoenix Long-Term Ecological Research site (CAP LTER). As part of their effort to document the landscape history of the region, the CAP LTER has produced a series of maps showing the historical boundaries of Phoenix and its surrounding agricultural areas from 1912 to the present day. The United States Environmental Protection Agency has also documented the growth of the city. We have animated the map data from CAP LTER and the EPA using satellite imagery from NASA and the United States Geological Survey (USGS) to illustrate how much Phoenix has grown. Canals are explicitly shown to emphasize the metropolitan area's dependency on surface water.