At the edge of the High Atlas mountains, a stream moves out into the drylands beyond. Along its length, a ribbon of date palm groves and small villages define the presence of human activity on the margins of the desert. The contrast between the desert and the date palms and the villages is stark.

This is the Wadi Rheris at Tineghir, a small town on the eastern side of the High Atlas mountains. A wadi is a stream that will go dry most years during the long, dry summer months. It is called "perennial" in this regard--the stream comes and goes, given the irregular nature of precipitation in the region.