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I'm working on a post-apocalyptic desert scenario in the near future where people live in small, loosely connected communities that trade with each other on a small scale and might have agreements regarding infrastructure use and maintenance and energy production such as establishing a smart grid. They are subsistence farmers and scavengers (to keep machines and computers running) but might cooperate for educational purposes and maybe even establish something along the lines of universities. They would be hampered by specialty and hard-to-make products not being available. Electricity generation would be completely decentralized and maybe not available around the clock. Clean drinking water would be infinitely more precious as even ground water might be salty. In general these communities would be very eco-friendly by necessity. Waste and pollution of common goods would be considered sin.

So the two biggest problems are the absence of fertile soil and water scarcity.

Water

I imagine you could use solar heat to desalinate sea water and transport it inland using pipelines. I'm not sure how energy efficient this is (if it was cheap it'd be used in all desert regions with sea access on a big scale) and going high tech would defeat the purpose as there wouldn't be a central authority keeping large and complex infrastructure projects running, only agreements between small communities to say maintain a stretch of road or pipeline. Also the power-differential arising from control over water distribution by one group of people could lead to conflict. This is way big centralized undertakings are to be avoided. Solar pumps could pump up ground water to be desalinated locally if need be.

Food

Do hydroponics present an answer in this situation or would you have to add other ways of growing food at the village level? You could farm vegetables and fish but you would need grain, right? Not just to make sure people get enough energy from carbs but also to feed it to livestock assuming an omnivore diet. I've never heard of hydroponics being used to grow grain. I also don't know how water efficient the technology is but I'm assuming it must be since NASA is working on it.

EDIT

Seems there's a consensus that hydroponics is out because it's too high tech and that the solution will be combination of aquaponics, raised-bed-farming of vegetables, and the farming of rabbits, chicken, goats and insects for protein.

I didn't know saltwater aquaponics existed (even though there's no reason it shouldn't). This suggests that the most popular fish for sweetwater aquaponics can be modified to tolerate salt water. It makes protein (and possible vegetable) farming using salt water look quite feasible.

The question that remains is how to reproduce fertile soil. I'm assuming this can be done using compost? Could an agricultural cycle be established that removes the need to "fetch" natural soil indefinitely once it's been going for a while?

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  • $\begingroup$ @L.Dutch True. Both use water but the technique is different. $\endgroup$ – H3R3T1K Sep 6 '17 at 11:28
  • $\begingroup$ You are right, my bad. $\endgroup$ – L.Dutch - Reinstate Monica Sep 6 '17 at 11:29
  • $\begingroup$ Desalination is actually cheap. The problem is that this cheap water is available at sea level, for obvious reasons. Pumping the water uphill to where it's needed is expensive and requires expensive infrastructure. $\endgroup$ – AlexP Sep 6 '17 at 14:27
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FOOD

The problem with the food can be solved with hydroponics and aquaponics. You can farm aquatic animals in tanks (aquaponic system). Eventually the water will be filled with excreta of the animals. The water can now be feed into a hydroponic system, you can use sand to support the roots of the plants. The water can again be used in the aquaponic system. Thus only a fixed amount of water will be needed.

Vegetables that could do well in a hydroponic garden (with a grain of salt) include artichokes, beans, lettuce, spinach, cabbage, beets, asparagus, broccoli, cauliflower, Brussels sprouts and peas. Vegetables that grow beneath the soil, such as onions, leeks, carrots, parsnips, potatoes, yams and radishes will also grow hydroponically, but may require extra care. Some crops to avoid are corn, zucchini, summer squash, and vining plants. They can be grown in a hydroponic garden, but they are not space efficient, and just not practical. They will dominate your whole unit. Your resources are better spent on crops more suited to the compact systems.

The main problem is that how to grow enough amount of food, you will require large enough space to grow food that can last a community for a month. The minimum amount of agricultural land necessary for sustainable food security, with a diversified diet similar to those of North America and Western Europe (hence including meat), is 0.5 of a hectare per person. I have no idea how much area per person will it take when speaking in terms with Hydroponics.
I would have suggested using normal agricultural method but since it is a desert scenario one can hardly grow enough crop in sand. The only problem in using Hydroponics is that the nutrients have to be controlled minutely

Water

Your idea about using solar pumps to transport the water and then desalinating it locally is good. But since the Hydroponics and Aquaponic uses large amount of water (for the first time i.e, during installation) when it comes to grow food for a community, the water supply must be steady in the beginning, to fill up large tanks to farm aquatic animals. And then have that same amount of water stored somewhere else, so that the the farming tank doesn't go dry when the water with excreta is being used in hydroponic system.

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    $\begingroup$ The pipeline idea could be used to transport drinking water that's been desalinated at the coast to get enough water for aquaponics initially. $\endgroup$ – H3R3T1K Sep 6 '17 at 13:15
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    $\begingroup$ Pipelines put your community at a risk of losing their source of water. Also, desert climate is quite hostile. It might make more sense for survivors to move closer to coasts. $\endgroup$ – Olga Sep 6 '17 at 16:05
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Soumyajeet Addya has a really nice answer but I've got a couple of things to add that I feel warrant consideration, firstly cereals; grains like wheat and barley only need a lot of water at germination and during early growth they then "harden off" on lower water regimes, thus you need only run new water into the system for part of the growing season thus reducing the total volumes you need to pump in. These are crops that also create straw/hay which can be used for livestock and draft animals. Secondly seawater farming; there are large number of projects that are using fresh seawater to farm salt-tolerant plants both directly edible species for human and animal consumption and biomass for fuel.

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    $\begingroup$ Wouldn't space be a consideration? Grain is grown in fields, not gardens. $\endgroup$ – H3R3T1K Sep 6 '17 at 17:04
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    $\begingroup$ Yeah space is always an issue regardless of methods, you're already looking at a vast set up anyway, the only noticeable difference between a normal farm and hydroponics on this scale is the substrate, a living soil on a farm versus a sandy/rocky, nutrient poor, bedding for hydroponic cropping. The caloric value per square meter on grains is good and you could in fact stack beds of grains vertically since they only need a relatively small space for upward growth. $\endgroup$ – Ash Sep 6 '17 at 17:21
  • $\begingroup$ Thanks Ash. It is actually almost impossible to grow grains like wheat and barley using the above process. But vegetables and flowers can be grown. Grains can be grown but that would require additional amount of fresh water too, which is hardly possible given the above scenario. $\endgroup$ – Soumyajeet Addya Sep 7 '17 at 9:20
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    $\begingroup$ @SoumyajeetAddya You can grow cereals pretty easily with hydroponics in stacked beds, there's a company near where I'm living that does it for stock feed, you just need a hell of a lot of room which you do to feed a village anyway. You actually need less water to produce grain, per food calorie, than you do for leafy greens. $\endgroup$ – Ash Sep 10 '17 at 11:22
  • $\begingroup$ Ohk! I didn't knew that. Thanks for letting me know. $\endgroup$ – Soumyajeet Addya Sep 10 '17 at 17:13
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Hydroponic and similar techniques need a lot of water very careful dosage of nutrients in it.

They are suited to carefully controlled environment and to avoid contamination. They are (normally) used in "factories" where everything is artificial and controlled, including sunlight.

If you have that much water and fertilizer your best bet is to setup normal soil cultivations, possibly in a greenhouse to minimize water dispersion.

You would gain nothing from hydroponics, while needing a stricter control.

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  • $\begingroup$ Aquaponics would be more efficient I think. $\endgroup$ – H3R3T1K Sep 6 '17 at 13:11
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Hydroponics is a technology you can use when soil is scarce but but water is plentiful. However in the situation you describe, water is also scarce. This will mean that hydroponics is not a viable solution.

Solar stills can be used on a small scale to evaporate and condense drinking water, normally they're only used in survival situations as there's almost always a better way of doing it. However as a technology it can be scaled up to produce reasonable quantities of water, but not practically to the point of producing industrial quantities of water. Powered methods of distilling fresh water from sea water or other contaminated water tend to be prohibitive on power consumption. That's prohibitive now, not just prohibitive post-apocalypse.

In short, your coastal villages can possibly generate enough drinking water for themselves and maybe some irrigation from a system of solar stills. They're not going to be able to produce enough water either to supply other villages or to run hydroponics.

Water efficiency can be improved by growing in raised beds and collecting all water run off to prevent wastage from irrigation. However in doing this the overall quality of the local soil will not be improved. Effort should be put into improving the soil as early as practical after initial survival issues are resolved.

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  • $\begingroup$ Is it prohibitively expensive even when solar power is considered? You wouldn't need to generate power and then use that to boil water but simply focus mirrors to evaporate water in a container. $\endgroup$ – H3R3T1K Sep 6 '17 at 13:30
  • $\begingroup$ @H3R3T1K, solar stills use a cover rather than a mirror, this conveniently also acts as a condensing surface, the whole thing is quite neat and can be made using a plastic bag, a rock and a pot to catch the water. The principle is the same as using mirrors but runs at a lower temperature, the problem is still "power" but in this case that translates to "area". $\endgroup$ – Separatrix Sep 6 '17 at 13:35
  • $\begingroup$ @H3R3T1K, I should also say that to get decent parabolic mirrors to heat water, you're a long way past post apocalyptic and into reindustrialisation. $\endgroup$ – Separatrix Sep 6 '17 at 13:47
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One of the possible options is aeroponics-based vertical farming. These systems use water mist and do not require soil. The water requirements are lower than for hydroponics. Vertical farming may result in higher yields than other options if you can provide adequate lighting, nutrients, and CO2.

Real world vertical farms use LED red and blue lights (can be a problem in your setting) to increase production. The environments are closed and fully controlled to create optimal growing conditions and to avoid pests contamination. A lot of work is automated. These farms usually specialise in leafy greens but can be used for growing grain as well. Dwarf versions of plants are more suitable but may be harder to obtain.

I think livestock is not an option in your case. You can try to raise rabbits but any bigger animal would consume too many resources, including water. The calorie output also will be too low to justify expenses. You might be better off with insects and bacteria as sources of protein.

As others mentioned, you can also do tank fish farming. But it might be more reasonable to build fish farms near the ocean and grow sea fish since they do not require desalination. It might also be easier to feed this fish because you will able to grow their food in sea water. A coastal community then might specialise in growing and processing (canning, curing, etc.) fish and trading it for other goods.

There is a caveat, though. Depending on a number of survivors and level of automatisation prior to an apocalyptic event, any high-tech farming can be simply unsustainable. With the current technologies, once you run out of spare parts your system is no longer functional even if you have enough electricity to power it and people who are qualified to maintain it.

Unless you can start re-industrialisation very quickly, you will be better off figuring out how to produce food using low-tech methods. It will be more sustainable in a long run.

Edit: To think of it, there is a lot of food that can be grown in brackish water. You can farm all kind of molluscs, grow kelp (seaweed), farm fish and shrimp. There are also salt-tolerant plants that can be grown for biofuel and food.

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  • $\begingroup$ I don't think aquaponics is particularly high tech. I've seen one doomsday dude do it in his swimming pool. I think the problem with salt water fish farming is that these are predator fish that require so much fish to be caught for them to eat that it's not particularly sustainable. Heard that about salmon and tuna. That bit regarding protein from rabbits and insects is particularly interesting! $\endgroup$ – H3R3T1K Sep 6 '17 at 14:27
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    $\begingroup$ Well, when you have limited water, everything becomes high-tech due to reclamation and desalination issues. As for fish, find something herbivorous that can be sustained on algae and aquatic plants. Something like tilapia might be your dream fish. They are very easy to grow and are very adaptable. When fresh water is scarce you have to maximise your calories coming from sea water and to optimise your system to get the biggest bang for the buck. $\endgroup$ – Olga Sep 6 '17 at 15:14

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