Make the Drought Evaporate!

My read suggests that OP is probably less interested in increasing evaporation overall (though it would increase) than controlling where the water enters the atmosphere. There are places that are dry only because there happens to be a mountain in between them and the ocean, for example. Moving the water a long way is something we already know how to do (think oil pipelines, but containing salt water instead of hydrocarbon slurry). If it scales, this could make a substantial difference to such places.

Downside is that weather is the output of an insanely complex set of interconnecting natural systems and cycles. Making changes to the climate of a region this way will have unforeseeable side-effects over vast distances. Given the likely cost laying pipe over a mountain or whatever, I doubt many governments will be willing to take the risk of their big expensive weather-modification project provably messing up rainfall patterns or creating geologic instability or something in another state or country and having choose between paying enormous damages or eating their sunk construction costs. Most likely they would be unable to make that decision in a timely manner and default to doing both in the long run.

Then again, fracking, so I might be wrong about that.

My guess would also be that if there is airflow over the ocean the air would hold most of the water you could hope for with such an approach.

Let's do numbers! The first consideration is: it doesn't matter how many threads of yarn, over what distance traveled or residency-time, as long as the air that passes into the yarn-array comes out of the yarn-array near saturation, say 80%+ humidity.

So, suppose we erect one of these arrays around the entire perimeter of the dead sea. That's 135km, but wind only comes from one side, so let's round down and assume we're only benefitting from the projection's length - roughly 85km. Now, it seems that the dead sea gets decent wind - often above 8km/hr, but let's round that down to 3km/hr to be safe. If we're pumping to trays that drip onto wet yarn in layers, with the top-most being 4m high, then we can measure the amount of air that passes through these arrays in a day, and estimate how much water they would transport! (Remember, the trays may extend hundreds of meters, before saturation of the air... 'depth' of the array is set locally, and doesn't change the total amount of water at saturation.)

So, 3km/hr - 0.83m/s, and the array is 3m tall, for 2.5m/s air-flow per 1 meter of shoreline. There are 86,400 seconds in a day - 216,000 m3 pass through that 1m wide section of the array, each day. And the projection along the shoreline is 85,000 meters long! That's 18.36 Billion m3 of air per day. How much water would that hold? Ah, night-time temperatures are too cold, so we would have to cut our rate in a third and just use the daytime rate, to be safe again... And, winter is similarly cold; knock the total down to 1/4th. Of 25C or more.

20C holds 17grams of water per m3, 30C holds 30grams. Higher temps absorb water supra-linearly. Let's call it 20 grams of water per m3. And, we decided to cut our volume to 1/4th, accounting for times when "the wind is blowing, but it's chilly", giving us 4.59 Billion m3. Multiply that by 0.02kg - for 91,800 tons of water per day. That's not seven million tons a day; seventy times less!

Yet, as I mentioned, you would want solar concentrators to power the pumps, which will convect and drive a draft, multiplying the quantity of air-flow per day, and thus the water transported. With dispersed convection, you can mix-in dry air to evaporate a second round, further from shore. And, I only used 3m tall trough-and-yarn stacks, when we could easily construct permanent scaffolds many times higher. That same mixing happens while transiting the open waters, so opposite shores do have a chance to add to total evaporate, as well.

More importantly, the dead sea is small - the whole salty coast just west of it is 640km, for an eightfold increase in air-front. Consider also that your "2 million cubic meters" sounds big... but it's only a yard deep, less than one square mile big. It's only about 3,250 acre-feet, or almost a million bucks in rain, here. And, the desert isn't a desert because "the Dead Sea isn't evaporating enough" - it's the downdraft of dry air resulting from the Hadley and Ferrel cells meeting. The Dead Sea is fighting a continual desiccation-front.

So, just like it has every ten-ish millennia, a shift in sea-breezes and humidity are able to overcome that barrier, leading to an accumulation of water - the Sahara has done this many times. Once you hop over the threshold of 'all those first 3 million m3 evaporated', then the rest accumulates. Wondrously, once vegetation arises, that increases the daily convection, driving more sea-breeze, more rain. Sahara, again, demonstrates this. The initial shift in humidity was small, yet still enough to feedback into cycles of greening.

Further, considering that we only pumped the water up a few meters, needing some 100kJ per ton, then our operation provided that water at 1/100th the going fuel-rate, and more importantly - less expensive capital equipment. If desalination is 1/100th the cost, then even if only 2% of the rain fell on your own land, it's still better than laying irrigation. Ask anyone in Ag!

Evaporating into the 'wild' isn't profitable, so it's understandable that no one sought this route - I only expect a government to fund it, because they'd see returns in taxes regardless of which farm got rain. There's also a loooong history of simple solutions going unnoticed for decades; I mentioned a few when Julia Wise argued the same on the EA Forum cross-post [EA · GW].

Another example of "simple-and-ignored" to add to the mix: last year, a mathematician was in a class on Knot Theory, and the teacher mentioned that "the Conway 11-Knot is unsolved"... she took a look at it, thought about it intermittently for a few days, and came back to her teacher saying "What about doing it this way?" She was right - Quanta magazine wrote her up! It turned out, EVERYONE had missed a simple solution, after writing it up in journals, grad students struggling in vain hope, Conway himself miffed, for FIFTY years. Yup. Simple is invisible, sometimes.

Geopolitical issues are only certain regions. Others, like California, are begging for evaporators! Australia? It's all just one contiguous desert, and they were trying cludgier water pipeline projects decades ago. Southeast India, too. And if Libya only received a quarter of the rain they threw into the air, it'd still be good for them.

Lithium ponds are doing a separation; they are intentionally not evaporating as fast as possible as much as possible. A better area of industry to look at: spray & contact cooling. When machines or air-flows are hot, we create a lot of wet surface area, and we measure the evaporation from those surfaces. By having hundreds of yarns per square yard, hanging in parallel, you expose the air to hundreds of times more surface area than a pond does. And, the air-flow moves among the strands, while ponds create a layer of 100% humidity that buffers further evaporation. When industry wants to cool things, they use wet surface area, and a dense array of threads maximizes that surface area.

For salt, I already mentioned: you either have to drip it across the wide ocean, to avoid over-salting the water (the halocline is an invisible barrier to life)... OR, you pile it into a vast pyramid. That pyramid could be a tourist attraction, considering how many folks visit salt flats to ride kite buggies or burn art pieces while on drugs. To prevent salt leeching into the surrounding landscape, you first pick a large rock outcropping - granite is best. Then, surround with more rock to form a foundational retaining wall, gravity-style. Fill the basin with a layer of sand, two inches. Hire all of Elong Mush's workforce, to blast the sand-bed with THERMAL LANCES (which will need a welding torch to ignite ... wtf?!?), melting it into a contiguous glass bottom. Repeat a few times for good measure. Spew brine on top and let it evaporate into a salt-flat piling for decades. Bonus: because you hired all of Elong's bruhs, his empire collapses and the world wakes to sanity!

Flash floods are when a hot & humid 'atmospheric river' of some 100km wide, 2km thick, thousands of km long, bashes head-long into mountains or a cold front, like a long locomotive piling-up at a painted tunnel! Evaporating from rows of yarn into the air from the shoreline is a steady addition, which is accelerated only when the air is drier and warmer... the exact same times you don't have to worry about a flood. To give you a sense of how much 'water per area per day' we would be adding, for agricultural purposes: you can get good grasslands on 300mm/yr, or just 1mm per day... and evaporate would be spread mostly evenly, with hotter summer months seeing perhaps triple - 3mm, or an eight of an inch. It's a drizzle, but it would come in the hot, dry months, when the plants need it most.

For wicks, that's not really an engineering problem. Fiberglass is inert, and it wouldn't be disturbed; salt accumulation is just flushed with higher water levels => higher flow rates. And, desal megajoules are on wikipedia; though be wary, because the most energy-efficient method also has the most capital-expense, such that the final cost of water is far above the "1cent per Megajoule" cost of energy, above. "1cent per Megajoule" is near the good end of solar concentrators - Morocco's is about that much, on-site, if I recall. Being in the desert, I expect solar would be on the cheaper end. [[That translates to 3.6cents per kWh, btw, and by the time it gets transmitted with losses, with profit and transmission-capital expenses, folks usually pay triple.]]

I hope that helps clear-up some details!

Ah, thank you so much! That first Nature article is inspiring - I'll be twiddling my brain-thumbs tonight. (Sadly, it seems sea water's salt and particulates might gunk-up their evaporator-engine's pores; it would be excellent to deploy for the fresh water bodies that accumulate as a result of sea-water evap, regardless!) That article mentions generating a third of a terawatt, and saving a hundred billion tons of water, in the US alone, which would be spectacular - I hope that they can keep capital costs down, when they get devices out of the lab.

Desiccant cooling is sweet - you can also use cold desert nights to make ice in shaded ponds, (Persians were first, I think...) and if that gives you brine for salt, add the salt back to the ice for even lower temperatures! And, atmospheric water harvesting is lovely, especially the small-scale, low-budget stuff for people denied infrastructure and credit. You could definitely add dew-nets deeper in a large desert, to increase the residence-time of any moisture that traveled so far, multiplying the accumulation from yarn-evaporators!

Most of all, thank you for linking Metaphor Search! Your hope has been fulfilled - and I hope you were able to rest well!