Much of the modern world’s agricultural productivity, industrial activity, and high degree of urbanization is dependent upon the pumping and exploitation of limited freshwater resources. In some regions the water that is being relied upon is so-called fossil water — that is, water that was deposited many millennia ago and is mostly not being replenished for whatever reasons, such as lack of rainfall or impermeable geologic layers like heavy clay or calcrete laid on top. As these fossil water reserves are depleted, there is often nothing to replace them (the one notable exception being the possibility of desalination in some regions), with the eventuality often being large populations, industrial infrastructure, and farmland that is untenable in the regions in question, to be followed by mass migrations out of such regions. Particularly notable regions that are dependent upon fossil water are the American Great Plains (the Ogallala Aquifer), northeastern Africa […]