They work brilliantly in places with low humidity by high temps - i.e. Arizona, California and my personal experience - towards the middle of Australia.

Yeah they will work nicely in any "dry" desert. They do require access to significant amounts of water, though with the nice side-effect (for the context) that they also act as humidifiers,.

> Yeah, swamp coolers are great in theory

For me, they're great in practice. And I don't live in a dry climate.

I'll do anything to avoid living in a humid place, though. I can take very hot temperatures, but not hot and humid. At least when it's hot and dry I can still enjoy the outdoors.

The places most in need of cooling are those with high wet bulb temps, which are typically high humidity places. I've lived in the south east USA my whole life, and I cannot even imagine adding more humidity to my air.