Friday, May 23, 2008

Have You Ever Drunk a Cloud?

High along the jagged cliffs of Serra Malagueta Natural Park, a series of green nets billow in the wind, like a half erected modern art installation. They are, in reality, fog collectors that harvest water from the clouds that shroud the park in almost year-round mist. The technology is simple: water collects along the mesh surface, forming droplets that fall into a gutter below. The water passes through a tube, arriving in a tank to be distributed to communities.
How much water could that possibly provide? More than you might think. Fog contains .05 to 3 grams of water per cubic meter. Serra Malagueta, which receives only about 900 mm of rainfall per year, has a semi-permanent layer of “stratocumulus”—low lying clouds—pushed upwards from the coast by the mountains themselves. Thanks to these clouds, Serra Malagueta’s 120 meters of netting (8 installations) produce approximately liters per day, with production reaching 75 liters per meter of net per day in the rainy season. That’s a big help for the park’s 488 families, who rely principally on local springs, wells, and private cisterns for their water. As rainfall diminishes and ground sources dry up, 80% of the community continues to work in agriculture, making fog water a much needed alternative.
Fog collectors were first developed in Chile in 1987. Before researchers installed nets in Chungungo, this high-fog, low-precipitation community had always depended on trucked-in water. Now it is able sustain itself and even grown crops and trees. South Africa, the Dominican Republic, Israel, the Canary islands and Nepal are also benefiting from this ingenious technology.
The benefits are manifold. Fog water is free from microbes that contaminate ground water, requiring no treatment. Construction materials—mesh, plastic tubing, and wood or metal poles--are cheap and readily accessible worldwide. The most challenging aspect is positioning the nets accurately.
Despite the enormous potential, fog harvesting does not constitute a major source of water in Cape Verde. While 1133 hectars are considered sufficiently foggy, fog is currently harvested only on Santiago (though experiments have been conducted on Fogo, Sao Vicente sao Nicolau, Santo Antao and Brava as well). With steep desalinization costs, dwindling sub-soil resources, and abundant foggy areas, fog harvesting may yet become a viable solution for highland areas. National output potential is estimated at several million meters cubed of water per year. At that rate, a lot more people may be drinking clouds in the near future.


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