Earthshots: Satellite Images of Environmental Change

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Phoenix, Arizona, and its suburbs are growing rapidly, both in population and area. Landsat images show striking changes in the Phoenix metropolitan area in only a few decades. The most noticeable change is residential areas spreading over agricultural fields, which are shown in the images as bright red squares and rectangles. But in other areas, the urban growth expands over what was once bare desert.

New residents and tourists are attracted to Phoenix by the warm weather and abundant sunshine. Phoenix has maintained rapid and sustained growth, and its location in a wide valley allows neighborhoods to be built with houses that can have a lot of space around them. From 1970 to 2019, the population of the Phoenix metropolitan area grew by almost 410 percent.

Phoenix doesn’t have many cloudy days, so it’s perfect for studying urban growth with satellite images. Scientists and city planners study population growth and urban expansion in fast-growing cities like Phoenix to determine the changes that have occurred over time and to see how those changes impact the surrounding environment, affect the availability of natural resources such as water, and alter the landscape and how it’s used. That information can help people plan for future changes as cities continue to grow.

Population of Greater Phoenix

Map of the featured area.




The southeastern suburb of Chandler is the residential area near the center of these images. It was once separated from the other suburbs—in the 1972 image, it’s completely surrounded by agriculture. Agriculture still dominates the 1984 and 1991 scenes, but by 2001, Chandler is no longer distinguishable from the rest of the rapid suburban expansion.

In most of the residential areas, streets are laid out in roughly a square pattern. Most of the squares are 1 square mile in size. This pattern ends abruptly in the lower left of the images (especially noticeable beginning in 2011). This area marks the boundary of the Chandler city limits and the Gila River Indian Reservation.

New freeways and freeway interchanges can also be tracked as they are built over the time series. The large interchange on the west side of the 2011 image marks the intersection of Interstate 10 and Loop 202 (the Santan Freeway). In the 2001 image, construction of the interchange and part of Loop 202 can be seen.

Also prominent is the addition of several golf courses. The green grass of the fairways shows up as bright red patterns that look like sausage links, especially across the southern part of these images.

Population of Chandler




Images of the western side of the Phoenix metro area show the city growing out to meet Luke Air Force Base. The base, which opened in 1941, is in the upper left of the images. Just east of the base is an example of the typical urban growth pattern. The 2001 image shows a large bright area, which is the ground being cleared for housing construction. The 2011 image then shows this same area as a new residential area.

The Agua Fria River flows from north to south through the middle of these images. However, “flow” might not be the right word—the river is usually dry. North of Phoenix, the New Waddell Dam keeps much of its flow in the Lake Pleasant reservoir. The reach of the river seen in these images is below the dam, and the river flows only when water is released from the dam.

A reliable marker of urban growth, freeway expansion, can be seen here as well. Although Interstate 10 does not exist in the 1973 image, it’s the main east-west route seen in the rest of the images. In 1991, a north-south route, the Agua Fria Freeway (Loop 101), is shown as under construction east of Luke Air Force Base. The freeway begins in the northern part of the 1991 image, and by the 2011 image, Loop 101 has connected up with Interstate 10. The 2020 image reveals even more freeway construction west and north of Luke Air Force Base.

Loop 101 goes right by a new stadium, only visible in the 2011 and 2020 images. State Farm Stadium, which opened in 2006, is where the Arizona Cardinals of the National Football League play their home games.

This retractable roof stadium can be seen as a bright white oval surrounded by dark colored parking lots. The natural grass field can be rolled outside to get sunlight, then rolled inside before a game. In a close-up of the 2015 image, the bright red pixels southeast of the stadium reveal that at the time the image was taken, the field was outside. An image from 2014 shows the stadium with the roof open and the field inside.

High-resolution images also show the stadium both with the roof open and closed. An earlier image from 2004 even shows the stadium under construction.

As Phoenix grows, the need for water rises. The Salt, Verde, and Gila Rivers bring water from Arizona’s mountains, but it’s not enough for millions of people. Groundwater is pumped to the surface, but this withdrawal lowers the water table, so it’s not the best answer.

Phoenix looked elsewhere to supplement its water supply and established the Central Arizona Project (CAP). Completed in the early 1990s, this system of canals, pumps, and tunnels brings Colorado River water along 336 miles of canals to Phoenix and Tucson.

Part of the CAP is an expansion of the Waddell Dam that forms Lake Pleasant on the Agua Fria River. The New Waddell Dam was completed in 1994, and it increased the size of Lake Pleasant, which is evident in these images. Construction of the new dam can be seen in the 1991 image. 

Lake Pleasant water is only partly from the Agua Fria River. The lake also receives water from the Colorado River, over 100 miles away. A canal, which can be seen in the 1991 image, pumps water uphill from the canal to the lake in winter. During summer, when electricity and water demand is high, water is released through a hydroelectric power plant.

One drawback to this impressive engineering feat is that Arizona must share Colorado River water with Los Angeles and San Diego, California; Las Vegas, Nevada; and the irrigated fields of the Imperial Valley. Recent drought in the western United States has meant less water to go around for these large cities.

Meanwhile, urban growth continues to expand north of Phoenix closer to Lake Pleasant. In the 2011 and 2020 images, this growth is evident, including construction of a new freeway (the bright curvy line). Can you find where the new golf courses were built?


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