In an arid valley near the village of Kourtimale in southern Djibouti, a tattered chain link fence marks the boundaries of what was once Abdi Guelleh's farm. Within it, there's not a speck of greenery in sight. Broken lengths of irrigation piping lie scattered in the dust. A derelict weather station stands in a corner amid a tangle of cables. Here and there, taps that haven't seen water in years protrude from the earth. There's little to hint at the fact that this lifeless 2.5-acre plot was once meant to be one tiny brick in one of the world's most...