This past weekend I was reminded that Phoenix is largely what it is today -- the 5th biggest city in the US -- because of two very important things.

Firstly, the city had to figure out water supply.

About 50% of the city's water supply comes from surface and groundwater, specifically the Verde River and the Salt River watersheds that are to the north and east of the city. And about 40% comes from the Central Arizona Project, which is a 541 km diversion canal that pulls water from the Colorado River and brings it through the state (terminating in Tucson). From what I have read, the CAP canal serves about 80% of the state's population.

Secondly, Phoenix needed A/C.

Air conditioning was first invented at the beginning of the 1900s, but it really didn't become ubiquitous until the second half of the century. And not surprisingly, it made the southwest of the US far more appealing. In 1950, Phoenix had just over 100,000 people. By 1960, the city had grown by about 311% to reach nearly 440,000 people. Apparently there was more construction in 1959 alone than from 1914 to 1945 combined. Air conditioning made Phoenix's summers bearable.

Air conditioning is such an interesting topic because it's one of those things that many of us take for granted. When you walk into a store or an office building in the summer, you expect it to be cool. But it hasn't really been around all that long and its invention has, in many ways, been instrumental in defining the modern city. Even something as common and banal as a glass office tower with large floor plates would not be possible/practical without air conditioning.

We can certainly debate how sustainable it is to urbanize and air condition desert climates like Phoenix, but there's no denying that air conditioning has had a profound impact on our urban landscapes. Diversion canals are pretty important too.