Don’t even start trying to work out how bad the water wars would be if everywhere was like Phoenix.

Water rights between states and between nations are going to lead to war and mass migration.

Too hot to fight!

That’s why I’m glad I already live in the Pacific Northwest. At some point I imagine there will be a huge influx of only for our plentiful water.

I'm not sure what you mean by "there" because metropolitan areas typically do not have much agrarian enterprise, but Arizona grows plenty of cotton, beef, and citrus, and always has.

https://extension.arizona.edu/arizona-citrus-resources

https://www.arizonabeef.org/the-beef-story/cattle-in-arizona

https://www.cooperranchlife.com/contact

https://azgrassraisedbeef.com/shipping/

Of course, the urban landscape as it is now, used to be dominated by farmland, and so it isn't what it used to, but if you meant to write "they can't grow food there" that also another lie, because there is plenty of food that grows quite well here. In fact, several of my friends love to share the produce from the trees in their yards and their backyard gardens.

I think they mean at a certain point there will be no water to grow plants and it might even be too hot to grow them even if there was water.

Why would this ever be the case? The planet is 2/3s water

It’s 2/3 salt water. Desalinization is resource intensive, and water transport is fraught with geopolitical peril.

If only there were some method of extracting fresh water from the sky, somehow

Not if Arizona receives less rainfall, as predicted.

That is mostly sea/ocean, a lot of desalination would be needed

You might want to look up what happens in Yuma and the Imperial Valley, where it can be even hotter, because 1000ft lower elevation. People have been farming the Salt River and Gila River valleys for many centuries. I see that wikipedia has got a nice article on the Hohokam people, and the large scale network of irrigation canals they built.

Not much happens in the summer, that's true, but since all SW ag is irrigated, a lot is grown during the rest of the year.

Now I can't stand Sonoran Desert summers, not possible to be outside comfortably, but a lot of people really like the rest of the year there.