It’s been known for a long time, decades in fact, that a lot of the American population was moving to so-called Sun Belt states. The advent of air conditioning had a lot do with this, as the hot summers of such states were finally tolerable, giving residents access to the far more comfortable winters than were previously put up with in the Rust Belt and Midwest.
Arizona is one of the Sun Belt states, and one of the few that’s not actually a coastal state, as the rest sit on the Pacific, Atlantic, or Gulf of Mexico coastlines. That hasn’t stopped people from coming here though, although not all do so the whole year long. The seasonal population swings in Yuma AZ certainly reflect that.
The first group that can be attributed to this is retirees. Those in the Southeast are familiar with ‘snowbirds’ that spend their summers in the mild weather of the Appalachian mountains of Georgia, the Carolinas, and Virginia, moving to Florida for the winter months. Arizona has similar patterns, with some residents spending winters here but their summers in California, Oregon, and even Washington.
The second group is not always fully documented, as it is migratory labor coming to work the farms, ranches, fields, and orchards surrounding Yuma. Some are citizens, but others cross the nearby border.
The third and final group that impacts the local population count is often tourists. Many love coming to Arizona for at least a week in the summer, as every family should take a great road trip across the American West at least once in their lifetimes. Some love Arizona so much that they do a short-term rental and call a city like Yuma home for a few months before having to go back.