What amount of water should be evaporated daily from a desert location such as Sahara, in order to minimize temperature fluctuations of night and day?
In theory, how much water should be evaporated daily in order to create a barrier of protection over Sahara desert and maintain its temperature in a sustainable state?
Since there is a descending air column on the Sahara, you're fighting uphill. https://en.wikipedia.org/wiki/Sahara suggests you are getting 2800 kWh/m2/y of sunlight, and if you were to evaporate all of that heat away, it would require 8400 kg/m2/y of water. That's a column of water 8.4m high - you don't have that without using the ocean, which would deposit 295 kg of salt/m2/y. That's a layer about 13 cm thick.
This moisture would then blow away, and cause heat to be released during condensation somewhere else - likely some place that already gets rain, so it may not be helpful - raising the night time temperature there. http://www.esrl.noaa.gov/psd/people/quan.xiaowei/PDF/HCpaper.pdf suggests you've got 10^10 kg/s of air movement, all around the earth, within the Hadley Cell. There will be local areas where you have less, and more, than the average, so the wind speed may vary muchly. I leave it to you to work out how much of the humidity that is condensing will occur in a desert area, but it won't be piles.
Someone (and no, I don't have a reference) thought that putting up a windmill that pumped water out of the fan blades would help the desert bloom. I dunno what happened to it, but if they were using sea water, it's now a dead area. If not, then the leaks may have kept some plants alive in the area.
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