Quite possibly, and for a very important and underrated reason: the fights over water are already starting and are going to get bigger and nastier over the next few decades, but the cities on the shores of the largest freshwater supply in the world will be sitting pretty. Detroit may have to spend its forty years in the wilderness (rather more literally than that phrase is usually used), but there's really no question about it coming back eventually. Not with all that fresh water close at hand.
> the fights over water are already starting and are going to get bigger and nastier over the next few decades
What do you mean by this? Cities in North America tend to be on rivers, and isolated poor location choices (Las Vegas, Phoenix, a few CA cities, etc) don't translate to problems in other cities since they are on different aquifer. As far as I can tell, there is no threat to the water supply in most American cities. Egypt/Ethiopia's little water spat doesn't threaten water supplies elsewhere, fresh water isn't really a commodity like oil or iron is. If it was, there would be a killing to be made in fresh water arbitrage.
The water problem is a lot bigger than that. North American cities have mostly polluted the rivers they lie on and can't use them for a water supply. E.g. Atlanta gets its water from Lake Lanier, not the Chattahoochee. New York gets its water from the Catskills, not the Hudson.
Many cities are facing water shortages. Not just Las Vegas and Phoenix. The Colorado is tapped out, and California, Arizona, and Nevada have been fighting over it for decades. Rainy humid Atlanta was facing water usage controls for several years around 2007-2009. The Floridan aquifer is tapped out--developers are having to dig wells 1,000 feet deep these days to get water. Fracking is in danger of contaminating the Ogallala along with all the water that makes agriculture possible in the breadbasket. San Francisco is not yet in dire straights but Hetchy-Hetch isn't immune to the water problem.
These are all still localized problems, with local solutions (or that are in need of local solutions). Speaking about water shortages on larger scales seems to ignore the reality of how water supplies work.
Even if water was scarce in the US, it wouldn't be a problem in the US, at least in terms of residential use. Desalination costs less than a dollar per cubic meter, and a quick calculation based on existing pipelines gives me a price of about half a dollar to pipe that a thousand miles.
For comparison, water today, where I live, costs slightly under a dollar per cubic meter. So even if my calculation was off by an order of magnitude, desalinated water would be a reasonable option for all US households, well under other budget items like cost of food.
Industry that depends on cheap water might be different, but how much of that is stuck in places without good water supply?
LA sits very close to the ocean, and at the same elevation. Desalinated water using current technology costs $0.75/cubic meter (recycled water even less), and your average person uses 100 cubic meters a year. So, we're looking at a cost per person of about $6/month for water. With conservation you could easily get that down to $3/month.
And? The people that need water can get it no matter what the supply is. The industries that use huge amounts of water can adapt their methods to be less wasteful. And it will never stop raining entirely. I don't see water shortages causing real problems in the US, as long as we can predict them early enough to build compensating infrastructure.
The amount of water that you need is a few orders of magnitude more than what comes to your house. Even if you're a full vegetarian, far more water is required to produce the food you eat; and if you eat meat, well, you couldn't afford any of it if water would cost a dollar per ton.
The water used to farm isn't critial enough to anyone's daily life to be fought over. Specific areas might suffer from drought but not the entire country.
I'm not trying to suggest that if normal sources of water magically disappeared then things would be okay. I'm just saying that under possible circumstances there won't be any reason to fight to the death over water. Because of the desalination option, water shortages wouldn't be able to threaten anyone's life, only force businesses to adapt or move.
Also according to http://www.waterfootprint.org/?page=files/Animal-products even without any efficiency improvements caused by high water costs, pig would be $3 a pound more expensive and cow would be $7 a pound more. Easily afforded.
For background see: http://en.wikipedia.org/wiki/Colorado_River_Compact. Basically growth of southern cities has meant demand for water from the Colorado river has gone up while rainfall in the region has decreased. There is still a surplus right now, but that won't continue indefinitely.
While you make a good point about resources being finite, and people that can access those resources when said resource is scarce fair better than those who do not (especially water), you're point is actually a non point.
With such speculation, I could have a premonition of an alternative future where the initial settlers near all freshwater die, as the more aggressive and desperate peoples fight for the area, and this potentiality has as much merit as yours.
Also, why even say Detroit will come back if the original inhabitants are all but gone, and the area has been resettled by others? If Detroit's coming back in 2045, then [insert any maritime city/town/village/location/space] is too!
