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If you concentrated sunlight to points in the ocean, could you make the water evaporate significantly faster to induce a substantial amount of rain? Assuming you could do that, could you use silver iodide to bias rain toward certain areas of land?

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    $\begingroup$ Is there any reason this should be more efficient than, say, tried-and-true desalination plants? I'm reasonably certain most of California's utilities (and transportation) shortcomings are the result of human ineptitude more than location. $\endgroup$ – user10851 Feb 27 '14 at 4:14
  • $\begingroup$ @ChrisWhite desalination plants typically run on electricity, so if you were going to make them solar powered you'd suffer all sorts of conversion losses. So in principle I suppose this idea could be more efficient. However, I imagine it would involve huge numbers of mirrors, out in the ocean where they'd get dulled by salt deposits and be impossible to maintain; and directing the resulting rain would be no easier than controlling the weather more generally (i.e. not practically possible yet). It certainly wouldn't be a short term solution to today's crisis. $\endgroup$ – Nathaniel Feb 27 '14 at 8:22
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    $\begingroup$ @Nathaniel: I'm pretty sure that Dick Cheney has/had a weather controlling device. $\endgroup$ – Kyle Kanos Feb 27 '14 at 14:01
  • $\begingroup$ On large projects like this one needs calculations and data : how much humidity with what wind conditions etc to aim at reproducing rain cloud conditions. Maybe a modificatin of "salter ships" would be a better solution rsta.royalsocietypublishing.org/content/366/1882/3989.long . $\endgroup$ – anna v Jul 4 '14 at 3:45
  • $\begingroup$ Mirrors could be on the shore. not good for tourism of course but good for maintenance $\endgroup$ – anna v Jul 4 '14 at 3:50
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I don't think it would be a good idea. Solar power plants are effective only because they direct light beams to a small area, which result in high heat rate concentration. To make the water evaporate "significantly" faster You would need huge amount of mirrors or else the heat rate concentration would be too small to make a difference.

Answering to the second question, as far as I know, silver iodide, dry ice or liquid propane (used in methods of cloud seeding) can affect the intensity of precipitation from existing clouds or cause existing clouds to grow rapidly, but I don't think they can help forming clouds on a clear sky.

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So, you use mirrors to focus sunlight onto a small area of water to increase the evaporation rate, and making the air at that point more humid. But the mirrors are deflecting the sunlight away from other areas of water. This lowers the temperature there, reduces the evaporation rate, and decreases the humidity of that air. So you have low and high humidity in masses of air on a scale of at most kilometers. How long before turbulence eliminates these variations and puts you right back where you started from?

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  • $\begingroup$ note you could use parabolic mirrors from the shore so you would be cooling the shoreline while evaporating the ocean $\endgroup$ – anna v Jul 4 '14 at 3:37

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