The Subtle Cabinet, 26th Day of Hagwinter, 525 M.E. (Aldebaran): Tehran is about to run out of water, and we'll son learn what it's like when a city of nine million people don't have drinking water or sanitation. Tehran has done little to endear itself to Americans (and vice versa) but I don't wish what I fear is going to happen on anyone. 

In a world where immigration and mass migration is a geopolitical flash point, eight million displaced Iranians won't exactly soothe tensions. Already, the water shortage is one of the reasons Iran is expelling millions of Afghan refugees and why there has been fighting at the border.

Water's scarce in Texas, too. Part of the problem is the state’s antiquated approach to water policy, writes Rachel Monroe in The New Yorker. "Texas follows the rule of capture, also known as absolute ownership, which allows landowners to draw as much water from below their property as they’d like, even if this has a negative impact on neighboring properties." The rule of capture incentivizes over-pumping, as the more water you pump, the larger the area of a well's influence. Property owners in Texas can’t prevent someone next door with a bigger pump and a deeper well from sucking groundwater from underneath their property. "I'm drinking your milkshake." Every other Western state has abandoned absolute ownership, opting instead for “reasonable use,” but Texas culture holds private property sacrosanct, and state lawmakers can't seem to move beyond absolute ownership. 

Despite their challenges, Texas is still courting large, water-intensive industry in the name of "economic growth," an it's not difficult to imagine a Tehran-style future for the Lone Star State. 

Since the 1950s, over-pumping of groundwater has caused the ground surface to subside by as much as 12 feet in the Wilcox Basin east of Tucson, Arizona. According to the Arizona Geological Survey, over 3,000 square miles of the state are affected by subsidence, especially in urban areas. Large, populous cities in the desert are not long sustainable as Tucson and Phoenix and SLC are learning. The indigenous Pueblo culture in the area have already learned, as their once vibrant civilization fell into decline around the year 1300 due to drought.

Migration to the US from the Northern Triangle in Central America was due to drought, crop failure, and back-to-back hurricanes. The civil war in Syria was a direct result of drought. Drought and food shortages kicked off the Arab Spring. Drought even reportedly doubled the rate of forced child marriages in Ethiopia, as child marriage provides income to an impoverished family while removing one mouth to feed. 

Water will eventually become as valuable as oil.