The Namib receives an average of less than 25mm of rain per year at Sossusvlei. In the driest years, it receives none. By any conventional definition, this is not enough water to support a viable ecosystem. And yet the Namib supports extraordinary biological diversity: hundreds of plant species, over 100 bird species, a full complement of large mammals, and a community of small invertebrates so remarkable in their adaptations that they have attracted scientific study from around the world.
The explanation is fog.
The Benguela System
The Benguela Current flows northward along the Namibian and South African Atlantic coast, carrying cold water upwelled from the ocean depths. Cold ocean water chilling warm air above it produces fog, which rolls inland on most mornings for up to 100km. At Sossusvlei, this means that on approximately 60 to 80 days per year, the air contains suspended water droplets that, while not falling as rain, are biologically available to organisms that can harvest them.
The Fog Beetles
The most celebrated fog harvesters are the Onymacris and Stenocara beetles, studied extensively in the Namib. On foggy mornings, these beetles climb to the crest of dunes and stand with their bodies angled into the fog flow. Water droplets from the fog condense on the beetle’s textured back surface and run toward the mouth, providing several times the beetle’s body weight in water from a single fog event.
The beetle’s back surface has been extensively studied by engineers and materials scientists; the texture that promotes fog droplet condensation and directional water flow has been replicated in experimental water-collection systems and fog-catching nets designed for water-scarce regions.
Welwitschia
The Welwitschia mirabilis is a gymnosperm plant that produces exactly two leaves in its entire lifetime, growing continuously and splitting into a writhing mass of strap-like tissue that can extend for several metres. Welwitschia plants can live for over 2,000 years, some specimens in the Namib Gravel Plains have been carbon-dated at over 1,500 years old. They survive on fog moisture absorbed through their leaves and on groundwater accessed by deep taproots.
Welwitschia does not occur at Sossusvlei but is common on the Welwitschia Flats east of Swakopmund, within the same Namib-Naukluft Park boundary.
Fog in the Dune Landscape
When fog rolls into the Sossusvlei dune sea, the visual effect is dramatic: the dune crests emerge from the fog as orange islands above a white sea, with the sun burning through in shafts that produce some of the most extraordinary light conditions available at Sossusvlei. This fog photography window is unpredictable and brief, but photographers who are already in position at the dune crests when fog arrives, possible only for guests with pre-gate access, encounter conditions that are impossible to plan for but unforgettable when they occur.
Fog season: Most common between June and September; arrives most frequently in the early morning and usually burns off by 09:00 to 10:00. The Benguela Current is strongest and the fog most frequent in the winter months.