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I'd love some science advice and facts for this question:

If they use wind power to bring up water from the ocean in the day time and spray it on prevailing winds going into land (i.e. 10-15 km from the coast using 200m high fountains), can they make it rain more in arid regions? What weather control can be done by bringing up water from the sea?

Here are some maths (probably wrong):

1 Kilowatt-hour lifts 1 m3 by 100 meters,

1 GW of wind turbines can lift about 10 Km3 of water to 100 m high in the air.

Currently we install 5-7 GW of windmills every year, the world total is 500GW.

So, if humans can lift 50 Km3 of water in the air every year, for a region like Australia, can't we give them a lot of clouds and rain?

NaCl is about 60 grams, H20 is 18 g, Air averages to 29 g, I found that salt vapor doesnt travel very far from the coast:

enter image description here

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    $\begingroup$ The problem is going to be salt. Sea water is extremely salty, and salt kinda makes it extremely hard for anything to grow. It would be better for there to be a drought than it would to salt the land. In sydney we do have a plant that is meant to purify salt water and make it drinkable, but that is an extremely costly process. In terms of generating rain fall, there are also pellets you can shoot into clouds. China did that to clear up their smog before the 2008 Olympics, however if it rains in one area, it simply won't rain in another. $\endgroup$ – Shadowzee Oct 9 '18 at 3:28
  • $\begingroup$ That's cool, I saw a graph of airborn salinity which said that it's divided by 10 at 1km from the coast. $\endgroup$ – com.prehensible Oct 9 '18 at 3:37
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    $\begingroup$ @Shadowzee not only killing all the vegetation, but making all the animals who drink rainwater die of thirst, and corroding everything else!! $\endgroup$ – RonJohn Oct 9 '18 at 3:37
  • $\begingroup$ "airborn[sic] salinity ... divided by 10 at 1km from the coast." Airborne salinity isn't that high at the coast either. But then you aren't actively spraying lots of seawater high into the atmosphere, either. $\endgroup$ – RonJohn Oct 9 '18 at 3:40
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    $\begingroup$ Wind patterns: Arid places near water usually have winds blowing the wrong way. $\endgroup$ – user535733 Oct 9 '18 at 11:52
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Rather than windmills, look at solar towers to send evaporated fresh water high enough into the atmosphere to generate rain: Getting large amounts of water to the Australian outback

As many people pointed out, salt would be a real killer for the project. The other factor which should be taken into account is the need for the water vapour to rise high enough to actually form clouds. If it is only being pushed a few hundred metres in the air, you are more likely to be creating clouds of fog rather than rain clouds. Pumping the vapour a kilometre into the air will ensure cloud formation, and allow the rains to fall inland.

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  • $\begingroup$ Fog isn't necessarily bad, though. It can make the coastal areas more habitable, which are typically the densest populated areas. $\endgroup$ – MSalters Oct 10 '18 at 7:19
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I might as well post an answer, because there are many different things I want to address about this issue.

Firstly, as I mentioned in my comment, salt isn't exactly good for plant growth. Secondly, salt is hard to remove once it’s been saturated into the land. Using salt water to to create clouds is going to generate large areas of simply unusable land because there is no way to remove the salt without digging up all the dirt and processing it. You can't even wash it out, because that salt will flow through the rest of the land and river systems making it extremely hard for plants to grow.

Secondly, pumping water is expensive. What you’re talking about isn't 10 or 20 km. Its 100s of kilometers of piping to get the sea water there in the first place. Believe it or not, the population of Australia is pretty much entirely focused on the coast, so getting the starting pipes past the cities is going to be expensive. As you go farther out, it gets worse, because it’s harder to get equipment there, it’s more costly in terms of pumping the water and every now and again, people will have to do maintenance checks on all the equipment. If any of the salt water leaks, you've basically killed off the usable land in that area, so you need to check it pretty frequently.

Thirdly, (not sure on the exact stuff behind this, so skip this if you want) salt water is a lot more corrosive than normal water. With normal water, you just get rust due to oxidization. In salt water, you have a number of electrolysis reactions which is going to accelerate that corrosion effect even faster. Since you’re also pulling the water from the sea, you need to make sure it’s free of living creatures, small particles and so on, so that any coatings you apply don't get scratched off and the pipes don't get clogged from barnacles and what not growing on the insides. So you can't just plug a pump and pipe into the ocean and call it a day. You’re going to need to build an entire filtration plant next to the sea.

Now the solution which solves most of that would be to filter the salt water, pump the fresh water inland and use it. The biggest problem is it’s ridiculously expensive to do that compared to just pumping water out of aquifers or water tables. You can treat the water with chemicals, filters and/or boil it. In each case it consumes a ton of materials and energy to generate the water required and a ton of waste materials that will also need to be treated (filters don't last forever, you make new ones, or pump water through them backwards to unblock the holes). So you have an expensive process with an expensive distribution network when there is a cheap solution under the farmers’ feet. Desalinization is important; in Sydney we have a desalinization plant. It just hasn't been used for a while (and is costing us money), however it’s a backup plan in case things get bad, not the solution to a natural problem.

Now I finally get to the turbines. Simply put, turbines aren't going to be efficient in spraying water everywhere. They do look like giant fans, and a misty breeze on a hot day is great but they have some issues. Turbines need to be situated in areas with high winds. That isn't going to be the most of Australia. Turbines are spread pretty far apart and heavily dependent on the wind; you’re not going to cover a lot of ground using turbines... you'll get patches of growth but not the lush green fields you would imagine. The Sun is hot and so is the ground. A fine mist of water isn't going to last long enough to get deep into the ground. You might think to yourself, but I mean heavy rain, not a fine mist like those spray bottles, but simply put, there is no way to move that much water. (Think of the firefighting planes. it looks like a lot, but farming takes a constant supply over a huge area, so just because you can water your entire backyard with your hose, doesn't mean it works for a national park.)

The best thing we can do is shoot pellets into clouds to make them rain. Nature does a far better job at moving water around the world than we could ever do. Sometimes it’s too much and you get floods, and other times there is too little and you get droughts. Changing nature can cause unintended consequences (a butterfly effect) that might not show up until many years or decades later (take global warming). If it rains in one area, another area where it should have rained is missing out.

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  • $\begingroup$ Thanks, the idea was to raise the water only 200-300 meters, like the tallest fountain in the world which is 300 meters high, using coastal windmills. $\endgroup$ – com.prehensible Oct 9 '18 at 7:56
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    $\begingroup$ @com.prehensible It would be easier to draw up the water, desalinate it, and then just use it for irrigation instead of spraying it into the air and hoping some of it will end up on your crops. $\endgroup$ – John Locke Oct 9 '18 at 11:54
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    $\begingroup$ @com.prehensible You should mention that you only want to use it on coastal areas, because when I think of Australia and arid, I don't picture anywhere near the coast. $\endgroup$ – Shadowzee Oct 9 '18 at 22:04
  • $\begingroup$ There is an dried inland sea in south oz, there was govt plans to build a river to it previously perhaps it would work with windmills, it just makes salt if it evaporates. I studied it, sry i didnt write coastal windmills, corrected. Thanks Shadowzee $\endgroup$ – com.prehensible Oct 10 '18 at 11:31
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Look up the Marine Cloud Brightening Project (or 'silver linings')

The Marine Cloud Brightening Project (MCBP) aims to test the premise that spraying a fine mist of sea water into clouds can make them whiter, reflecting more sunlight back into space. The MCBP, a form of Solar Radiation Management (SRM) began with indoor development and testing of spray nozzles, and is moving toward a land-based field test in 2018, followed by ship-based tests and a larger-scale sea test later on.

One of the unknown side effects is how this would affect rain fall.

The effects of large-scale testing of MCB geoengineering techniques are unknown, but could affect rainfall in the immediate area, as well as creating unpredictable changes to regional weather patterns at a distance. For example, marine cloud brightening in the Pacific and elsewhere may lead to reduced rainfall in the Amazon basin.

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  • $\begingroup$ This was my first thought but my memory was faulty and my google-fu was weak. $\endgroup$ – MongoTheGeek Oct 9 '18 at 17:54

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