Don’t Give up on Desalination

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How we manage local water sources drastically alters how we grow crops and get drinking water. Cape Town is currently experience a water crisis that was in the making for decades because of poor water use policies. Desalination plants can help coastal cities provide water to their populace by separating salt from seawater. Wired has a good article on how one company is improving desalination techniques for growing crops, which, they predict can help bring plant life to arid regions.

The structure’s double-layered fibreglass roof transmitted sunlight but captured heat, diverting it through ducts into a compartment at the building’s rear. There, the heat was used to distill freshwater out of seawater for irrigation. The rest was vaporised and sucked through the growing space by fans to cool and humidify the plants, reducing transpiration. Paton calculated that a square metre of crops adjacent to the greenhouse would have required eight litres of water per day to offset what they lost in transpiration. “But inside we were using closer to one litre per square metre per day, and we were growing a better crop.”

Paton is also interested in the long term restorative benefits of his invention. Davies’ model predicted that the greenhouse’s cooling and humidifying effect would seep into the surrounding environment: “You can see there would be a plume of cool air coming off the greenhouse,” he says. And since the region hasn’t always been barren, Paton thinks greenhouses could return parts of it to the naturally vegetated state it was in before overgrazing and drought took hold. “I believe that when you get to, say, 20 years, you’d have enough vegetation to do the job of the greenhouses because they’re creating shade and shared humidity – changing the climate.” Because vegetation sequesters carbon, that also has broader ramifications for mitigating the effects of climate change.

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