Municipal uses like drinking, showering, and watering ornamental plants is a tiny pct of desert water use. Most of it is crop irrigation, because if you can will water into existence then crops grow great in sunny deserts.

If the US' alfalfa exports to Saudi Arabia went down by 10%, we would never have a municipal water shortage in the American West in the next century.

Lack of water is a political problem. We have vast oceans which can be desalinated. Israel gets 85% of its water from desalination, they have gone from water shortages to having a water surplus.

We pump oil via pipelines vast distances, we can do the same with water.

We have virtually unlimited energy locked in Uranium which could power desalination plants, or heck you could power them with solar.

There’s plenty of water for the whole planet. There’s also plenty of clean energy (see nuclear and solar point earlier). But tapping these resources requires a functional government or at least a bureaucracy willing to allow companies to build.

There are people pushing for more shade in cities as an adaptation for a warming world. There is some crossover with the push for a reduction in cars and generally reducing the footprint of streets. Looking at old cities in hot climates I can see how this could make sense.

For Las Vegas, Cottonwoods are native and grow pretty quickly. Like many poplars they were used to grow shelterbelts.

I don't think anybody ever moved to Vegas expecting to be able to have a street life.