Phoenix
Desert city built on re-excavated Hohokam canals, named for the mythical bird rising from ashes. 5th-largest US city despite 46°C summers and 200mm rainfall. Colorado River drought now testing whether growth can override carrying capacity.
Phoenix should not be a major city. It sits in the Sonoran Desert, where summer temperatures regularly exceed 46°C (115°F), annual rainfall averages 200mm (8 inches), and the Salt River that gave the valley its agricultural start has been dry within city limits since the 1930s. Yet Phoenix is the fifth-largest city in America, with 1.65 million residents and a metropolitan area of 4.9 million that grew by over 750,000 people in the 2010s alone. The city's existence is an engineering proposition: without the canals, dams, and air conditioning that make desert habitation possible, Phoenix would revert to the sparse Hohokam settlement pattern that sustained perhaps 50,000 people in the same valley a thousand years ago.
The Hohokam civilization built over 200 kilometers of irrigation canals in the Salt River Valley between 300 and 1450 CE—one of the most sophisticated pre-Columbian engineering systems in North America. When the canals were rediscovered in the 1860s, Anglo settlers simply re-excavated them. The city's name was chosen deliberately: Phoenix, the bird that rises from ashes, building on the ruins of a previous civilization. The Roosevelt Dam (1911) and subsequent federal water projects guaranteed a reliable water supply, and the arrival of air conditioning in the 1950s removed the last constraint on growth.
Military installations during World War II—Luke Field, Williams Field—brought thousands of servicemen who returned after the war for the cheap land and sunshine. Motorola established its semiconductor division in Phoenix in 1949, seeding a tech corridor that eventually attracted Intel (which built its first fab outside California in Chandler, Arizona). The population exploded: 107,000 in 1950 to 1.3 million by 2000. Phoenix annexed aggressively—the city now covers 1,340 square kilometers, larger than Los Angeles.
The growth model faces physical limits. The Colorado River, which supplies roughly 40% of Phoenix's water, is in a multi-decade drought. Lake Mead and Lake Powell have dropped to historic lows. In 2023, Arizona restricted new housing developments in parts of the Phoenix metro area that rely on groundwater, acknowledging for the first time that the water supply cannot support unlimited growth. Semiconductor manufacturing (TSMC's $40 billion fab complex in north Phoenix) demands enormous water volumes. Phoenix's future depends on whether technology can continue to override the desert's carrying capacity—or whether the Hohokam's fate, abandoning the valley when the water ran out, is not a historical footnote but a preview.