An oasis from the air
Along the hyper-arid coast of Peru, where annual rainfall can be less than 5 millimeters, isolated patches of green appear on the coastal hills. These are the Lomas, or "fog oases," ecosystems that survive almost entirely on moisture collected from the dense sea fog, known locally as garúa. This phenomenon occurs along a 2,800-kilometer stretch of the South American coast, a result of the cold, upwelling Humboldt Current cooling the air above it, creating a persistent layer of fog.
The fog itself consists of tiny water droplets, between 1 and 40 microns in diameter, which are too small to form rain. But as the fog moves inland and is pushed up against the coastal slopes at elevations between 300 and 1,000 meters, the vegetation captures the moisture. Plants intercept the moisture, which then drips down to the soil. The seasonal bloom is most dramatic during the Southern Hemisphere's winter, from June to October, when the garúa is thickest and relative humidity approaches 100%. During this period, the barren brown hills transform into a lush, green area.