[lunar-whitey]

> Urban centers are not set up for large-scale rainwater collection.

This is correct. Even in suburban areas, rainfall may be irregular and supplies to collect it (and render potable, depending on the manner of collection) also unavailable to most people.

> What would actually happen is the military and national guard would be mobilized. They would use pumps and water trucks to visit acquifers and wells, and distribute water by truck neighborhood by neighborhood. A continuous stream of trucks constantly resupplying cities.

At this point, I will be explicit concerning my opinion of your 28 million direct casualty estimate upthread. I think this only makes sense if you think in terms of individual city centers being destroyed, which is a massive underestimation. Modern weapon systems with independent reentry vehicles and warheads yielding around 100 kilotons do not destroy cities; they erase whole metroplexes.

In such a scenario there are no major population centers left to supply or contingents of military to supply them at a meaningful scale. I don’t have much interest in arguing how survivors in outlying areas might migrate in response to the supply chain collapse that follows.

[0xbadcafebee]

With only 10 large metro-areas destroyed, there are still other very large cities and metro areas. Phoenix, Houston, San Antonio, Dallas, Fort Worth, Jacksonville, all have over 1M people. San Jose, Austin, Charlotte, Columbus, Indianapolis, Seattle, Denver, Oklahoma City, Nashville, all have from 700K-1M. And there's 20 more with 500K+ people. We have a big-ass country. Military and national guard are spread all over, as well as "industry" that is tapped in time of war (we don't have much of it left, but enough to be useful)

I'm not defending whatever OP's point was, I'm just saying we would have a whole lot of people left. Very few resources, and very poorly distributed, but a lot of people. If we lost 40% of the population it would still be a lot of people.

[lunar-whitey]

I think the 10 U.S. metro number itself is somewhat arbitrary here. It’s impossible to say precisely without looking at all parties’ deployed warhead counts and operational plans, but I have seen estimates that put the number of direct casualties over 100 million. (Russia and the United States each have well over 1000 warheads deployed.)

I do accept that towns far from both major metropolitan areas and high value military targets could survive. However, the short term social impact of supply shortages and the longer term agricultural effects of atmospheric changes are difficult to predict.