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The Earths oceans receive more precipitation than the land. Much of this precipitation happens in ecological dead zones such as the central pacific, southern Indian Ocean etc. So the precipitation doesn't really affect any ecosystems. So what can be done to move rainfall from those regions (even a fraction would match the precipitation on land) to places where it is needed (Central Asia, Sahara, Australia)? I initially thought you could take an oil tanker or something and harvest the rainwater on massive umbrellas but that is not nearly enough water to sustain even the smallest of rivers lol.

Edit- following comments to add the relevant tags. Someone already did some. Thanks for the comments.

Also, I would like answers that don't really have hard math and equations but more like what technologies present or in the works can be used for this. Thank you for your responses!

To help visualize, here's a map of world rainfall. You can see that much of it happens on the ocean:

enter image description here

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    $\begingroup$ Hello Guestacciguess, welcome to Worldbuilding. When you have a moment, please take our tour and read through the first two bullets of our help center to better understand our site. Thanks! $\endgroup$
    – JBH
    Jul 19, 2021 at 17:57
  • $\begingroup$ The question at present seems not about a fictional world, which is what we deal with here. Science-based is a great tag, but perhaps you could supply us some context in which you are building your fictional world? Technology level, types of civilizations, but most importantly - what you are trying to achieve, then maybe we can help you get there. You can edit to clarify. $\endgroup$ Jul 19, 2021 at 18:12
  • $\begingroup$ @ARogueAnt. This is why I asked my question about what the Science-Based tag's scope really is. I'm a fan of the idea of it meaning "use science as your starting point to create a fictional answer that tries to meet the condition of suspension-of-disbelief." I'm NOT a fan of it meaning "it's the hard-science tag without the requirement of citations and equations." $\endgroup$
    – JBH
    Jul 19, 2021 at 18:26
  • $\begingroup$ However, Guestacciguess, @ARogueAnt's comment brings up a point. If you read the science-based tag summary or wiki, you'll see that it is NOT allowed to be used by itself. You probably should add tags like water and climate. Click "Tags" in the left column to see a list of what we have. $\endgroup$
    – JBH
    Jul 19, 2021 at 18:29
  • $\begingroup$ For future reference (and not simply complaining that I didn't get the coveted green check mark...), we recommend that you wait at least 24 hours before awarding a best answer because we have users all over the planet who could give you a better answer or, at least, more to think about. Human nature is to stop caring about a question once the "solution has been found." $\endgroup$
    – JBH
    Jul 19, 2021 at 22:21

2 Answers 2

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The more important question: Do you need to do this at all?

The biggest consumer of rain water is agriculture. Most of the crops we grow at large scales require 30-65 cm of rain per growing season, but the average over-land rainfall over the Continental US is about 100cm/yr. This means that for any given area of farmland, you actually receive more water in a year than you need... so, why then are we operating at a water deficit? The biggest reason for this is back-to-back agriculture. By planting several crops in the same space in a year, using modern fertilizers to renew the soil between plantings it means that we can double or even triple the water requirement for a field pushing potential rain requirements above 100cm/yr... then there is of course the other issue which is that we generally get more rain than we need for part of the year, and less than we need for the rest; so, feeding rivers and aquifers also becomes a major source of inefficiency.

Now let's say that your goal here is really to maintain a back-to-back agricultural model, then let's start by trying to solve your much easier concern which is water conservation. By placing a troffed impermeable layer under your topsoil, you can significantly increase the efficiency of your water retention. Basically, this makes it so that you maintain a good layer of water in your soil that your mature plants can use as needed, even when rain is scarce. When you plant new crops you just pump it up from down there and spray the surface soil until your plants get big enough to reach the stored water on their own... and if you get too much rain in too short of a time you pump it up and sell off the water to other places that need it more.

enter image description here

So, even with back-to-back planting, the water budget is solvable in many parts of the world using just the water that falls on your fields, just by keeping it from flowing away and being careful not to plant back-to-back high water consumption plants.

But what about places that get less than the average rain fall? Sadly, the places that don't see a lot of rain over land tend to not be very close to places that do see a lot of rain over the oceans. So if you are in California for example, you only get ~50cm/yr and would benefit from supplementing your water from elsewhere, but most of the oceanic rainfall that happens in the world does so in the Western Oceans; so, it would either need to be pumping water all the way from the Philippines, across the whole Pacific, or overland all the way from the Gulf of Mexico, or you would very large rainfall collectors to gather a meaningful ammount of water... all 3 of these options are very cost prohibitive, even if it were possible. And that is not to mention, that most of the over ocean places that do get lots of rain get it in the form of hurricanes/typhoons which will probably destroy any kind of collectors you do try to set up.

Since these pipelines would be prohibitively long anyway, you are better off instead looking at closer overland places where you could set up the same sort of sub-surface troffes. So, let's say you could get the whole US down to back-to-back planting that required 80 or less cm/yr using these water retention systems, you could easily produce much shorter pipelines by taking captured water from East Coast land areas and pumping them to the West Coast. So, even if you turned the entire landmass of the US into nothing but cities and farmlands, you could still capture enough rain water to supply the whole country's water needs just by pumping from places that get more than 100cm/yr to those that get less.

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This is more complex than you might think

And this is a bit of a frame challenge. Collecting rainwater off an ocean would be no small thing. You can't just suck up the top tenth of an inch (even if you knew where the rain would fall). So this presents a more practical solution.

Also, the question changed after this answer was posted....

Climate is complex. When Douglas Adams said (tongue-in-cheek) that space is really, really big... that's how you should think about climate's complexity. It's really, really, complex.

So, let's throw technological limitations out the window and think about this problem.

Your target location is important. Watering a sea-level desert is different than watering a high altitude desert. But I believe your options are similarly limited.

Volume is your biggest problem

For example, Kansas City, Kansas in the U.S. gets an average of 39 inches (992 mm) a year. Kansas City (if we only consider the boundaries of the city and not any of the surrounding region) is 319 miles2 (826 km2). So, in one year we're talking about 0.2 cubic miles (0.82 km3) of water or 2.2e11 gallons.

That's a lot of water.

But that's what you'd need to move to duplicate the rain in Kansas City. You're not going to do that with boats.

Which means transportation is your next problem

If we want to toss realism to the wind, you could move all that water through an 8" (25mm) pipe with enough pressure. The pressure would be so high that it would probably initiate fusion or change the orbit of the earth or some other reasonably apocalyptic consequence.

Using this handy dandy pipe volume calculator and ignoring things like pressure, a 24-foot pipe will move 9 billion gallons 500 miles.

We would need 24 such pipes to move all the water we need, or we need a lot of pressure.

Next is desalination

The wonderful thing about the natural rain cycle is that it leaves the salt where it belongs, in the ocean. As it turns out, manually removing salt from saltwater is a glorious pain in the caboose. But we're ignoring tech limitations, right? Each of those 24 pipes would need a substantial (really, really, really big) desalination plant and you'd need a way of getting rid of the salt.

That last part is really important. You see, Mother Nature is leaving the salt behind over the entire surface of the ocean. In other words, the overall salt density doesn't meaningfully shift thanks to evaporation because She's drawing from so much water in the first place.

The effort of filling plane-after-plane with salt to gently spread it like your grandmother's ashes over the ocean would be... economically challenging. How to get rid of this much salt without bringing to pass a zombie apocalypse would make for a great second question!

Next is distribution

The easiest solution would be to let the water fill natural lake areas. This could be problematic as the initial erosion would be magnificent. However, it would basically work — but it's leaving the pooling of water in great enough quantities to create a local rain cycle up to the vagaries of natural geography. You'll probably need to help it along by creating a lot of dams.

Which don't always work. Remember how much water we're talking about! And remember that large man-made lakes like Lake Mead have had very little overall impact on the creation of new farmland — through rainwater. They've had a huge impact through the availability of irrigation.

Therefore, I recommend this route.

But if you want to be a bit more... fantastic...

I personally like the idea of pumping the water to the top of a mountain and pushing it through a honking bit sprinkler head. Twenty-four heads surrounding an area the size of Kansas City spraying out water 91 days of the year (which is the average number of rain days for Kansas City). It would look cool! It would create rain!

And it's about as technically feasible as building a stairway to heaven.

But I'm not a fan of technologically-feasible answers unless you've used the tag. Don't use that tag.

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    $\begingroup$ For the desalination, the OP is proposing collecting rain water; so, no you don't need to remove the salt, it just means you need a collector the size of Kansas city to gather 2.2e11 gallons gallons per year... if you assume the same rainfall as Kansas city. $\endgroup$
    – Nosajimiki
    Jul 19, 2021 at 18:58
  • $\begingroup$ @Nosajimiki Yeah... I ignored that because it's more unbelievable than even what I've suggested. I mean, think about it, what're we gonna do, throw out a 400 square mile tarp over the ocean? Whadayathink, do I need to identify my answer as a frame challenge? $\endgroup$
    – JBH
    Jul 19, 2021 at 19:05
  • $\begingroup$ I initially made that point as a starter to get people thinking. I already know its ridiculous as anyone can tell (I put lol for a reason). Your answer is very detailed but the question was is there any technological made of moving the rain clouds from the ocean to land. Thanks for your answer though it did give some ideas like the lake formation. Maybe it would be possible for Australia with their whole lake eyre basin thing. $\endgroup$ Jul 19, 2021 at 20:06
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    $\begingroup$ I agree that desalination is probably the "easier" option, I just wasn't sure if you read the question right. If it were me, I would include some statement to compare and contrast the benefits of desalination vs giant collectors before delving into the flaws of the lesser of two evils. $\endgroup$
    – Nosajimiki
    Jul 19, 2021 at 20:29
  • $\begingroup$ @Guestacciguess You literally wanted to know if it was possible to move rain clouds? Uh... no. There's no such tech (and if that's really what you're asking, then you need to get rid of the boat comments and be a whole lot more clear.) $\endgroup$
    – JBH
    Jul 19, 2021 at 22:12

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