Climate change and bad decisions from the last 50 years are starting to bite now. It’ll just get worse. Expect migrations and countries collapsing as millions of people are pushed to migrate for survival.
Water for farming and power stations are the things that will be hit first.
And it’s not just water going away—it’s impingement by salt as well.
A lot of water infrastructure needs minimum levels to function. Drinking water may be a small fraction of use. But if the big users deplete a reservoir below its minimum operational level, the fact that the dead water is enough to keep Tehran alive is more trivia than solace.
For those unfamiliar, climate change and drought are believed to be one of the major causes of the bronze age civilization collapse
https://en.wikipedia.org/wiki/Late_Bronze_Age_collapse#Droug...
But you have to admit it would be very funny if a theocracy was forced to abandon it's capital by forces of nature.
That said, we never had the climate change that strongly on history.
Some of these "bad decisions" are ignoring the old systems, and ways. The hubris of "modernization" as better.
The water systems of old Iran are fascinating, and well covered if you hunt around for the info. https://en.wikipedia.org/wiki/Qanat