In the long term, Las Vegas is in way more trouble than California. California has several sources for its water, and even though those sources are pretty pitiful right now, there are always be the emergency fall-backs of desalination (at great cost) or forcing the farms that use up 85% of its water out of the state (at great cost to the US food supply). Vegas meanwhile gets 90% of its water comes from Lake Mead, and if that dries up, people will simply have to leave the state. If this drought turns out to be an effect of climate change instead of just being a historically bad drought, it's really not going to be long before this is the situation.
I personally think that Vegas will be attracting a whole new set of tourists at the end of this century as the world's largest ghost town.
The solution for Vegas, given the vast amount of people and money there, will be to build coastal desalination plants and pipe the water inland. It'll cost a lot, and they'll do it in the next 30 years. It might be done on a 50/50 basis with California, sharing the plants.
A lot is a relative term though, is $50 billion spread out over 30 years too much to ensure Las Vegas has water? No, it's very cost effective in fact. San Diego's big new plant has a billion dollar price tag, but provides enough water for 300,000 people. Las Vegas has 1.4 million people in its metro area. In the grand scheme of things, this is a comically trivial problem to solve.
I have a counter prediction: Las Vegas will finish the century as the same engineering dependent marvel it is today. Except it'll be even more impressive.
Wouldn't it be cheaper to build the desalination plants on the coast and sell it to California cities/famers in exchange for water that usually goes down the Colorado River from Nevada to California. Pumping it upstream seems like a waste of energy and infrastructure when the cities in Southern California already want and need the water for their residents.
The problem isn't that there isn't enough water for Vegas passing through Lake Mead. Its that legally they are obligated to send it downstream. Nevada gets a meager 4% of the lower basin of the river, while California gets 58.7% [1]
It would make more sense to sell the water from those desalination plants on the coast than to pipe it that far uphill. But perhaps Las Vegas could trade it with California somehow and actually take the water from the Colorado.
I'd guess there are a lot of water laws in the way of that sort of financial innovation.
I think it is unlikely the citizens of California are going to be be willing to shoulder all the environmental damage required to move massive amounts of water from the Pacific Ocean to Las Vegas, even if the full financial burden is shouldered by Nevada.
Desalination would also work well with (future) cheap photovoltaic generated electricity. It'd be a perfect use for overproduction of electricity since the desalinated water can be stored easily.
That's $4B for construction and $1.5B for operating costs over 25-30 years. Let's say 25 years to be conservative. So $220M/year.
It's expected to produce 150B liters/year. That's $0.00146/L or $0.0055/gal.
Imagine switching to solar doubles the ongoing cost. This is conservative since solar isn't that much more expensive and there are costs other than electricity, but lets go with it. Then the cost goes up to $280M/year and we're talking $0.007/gal.
I personally think that Vegas will be attracting a whole new set of tourists at the end of this century as the world's largest ghost town.