Tatooine on Earth – about fog, dew and moisture harvesting (part 1)

Tatooine. An archetypal image for sandy, dry, desert. Like ours, but alien, with strange technology and strange industries. Like moisture farming. Almost the same as here, farming’s easy to imagine happening anywhere, but farming *moisture* is just different enough for you to be sure you’re in another galaxy, another world.

At least, that’s how I always took it. In the last few years I’ve begun to read more and more about moisture farming techniques that humans have used in various cultures and times across this planet, and it’s not that alien at all. It’s just not been necessary for us to use such techniques in a culture derived from the wet and wetter European North. However, as we start globalising information and start taking indigenous cultures seriously enough to ask them how they do something before telling them how they should do it, more such techniques are turning up. In hot climates like this, they have a particular use. They extend the season of freshly available water just a little, in some places by a lot.

One of the ways I tell the seasons turning is by the morning dew. In August I know winter has truly ended when the sun is strong enough but the air still chilled enough that the early morning light sets steam rising from the dew. In October, I know the seasons are further turning when we have our first morning without dew, then when we have more mornings without dew than with, and eventually when there is no dew at all. Across the four months of summer I watch the little green line on the weather graph that marks dewpoint, and watch it never get closer than a degree to the line showing actual temperature. Then sometime in March, the lines finally cross again. A quick walk in the garden first thing in the morning results in damp wet feet, though it might only last a short time. And I know that summer has ended, and autumn has begun.

The thing about this is that there is a month or two either side of our rainy season where the rain might be erratic – but the dew still falls many days. Captured instead of allowed to dissipate, and concentrated down to a few points instead of spread thinly everywhere, there’s enough moisture in the dew to keep a few plants thriving that little bit earlier or longer. Maybe early enough to establish seedlings ahead of the weeds that come when the rain starts, or long enough for plants to finish a full harvest cycle and produce fruit after the snails have gone to sleep for the season. There are also days without rain but where the humidity is high, in which we wish we could take the water out of the air around us and put it somewhere useful. And while fog is a rarity in Perth (I suspect due to our kindly ocean currents), there are places not so different to ours around the world where fog is much more common and predictable than rain. In those places there are old historic methods (and some new higher-tech ones) for getting clean drinking water from the fog.

So, how’s it been done, historically? Part 2 coming soon.

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