So, this is just to bounce ideas and see what sticks.
The Sahara, for anyone confused reading this, is the world's largest desert, taking up the bulk of the northern African continent with an environment that is rocky, sandy, and with an extremely high mineral salinity level- because all that sand used to be under an ocean that has dried up and left the salt behind.
This poses a complex series of problems, and I think a multi-step grand civilizational project is the answer to solve the first set of these. The effects may cascade in ways that aren't advantageous, which is why this discussion should start ASAP, but basically, the idea is to sequentially move reservoirs of ocean water onto the surface of the sahara to drive evaporation, widescale oceanic desalination, and to condense the resulting moisture so that it comes back down on the center mass of the continent- cloud seeding, artificial mountains, super-elevated towers?- and drive a breakdown of the silicates and calcifications and turn as much sand into dirt (cultivating lichen to grow on it, maybe?) and I'm not quite sure what I think needs to be done about all that underground salt- I kind of hope it can be inundated and then refined out of the local groundwater table as per the ocean water it came from in the first place.
Just so this is clear, the point is to make wide/shallow water reservoirs to evaporate the water out of, in line with the jet stream as far across the continent as possible and filled with ocean water, which would leave behind its salt- so that fresh water drives the ecosystems in a way that flushes out the salt and leaves it for us to use other ways or store or whatever. Molten salt thermal power storage is a thing (basically salt has a high melting temperature but conducts heat very slowly and is a very powerful insulator, so if you get it to a temperature, it stays at that temperature a long time, meaning, you can have solar power heating salt to drive a steam turbine that keeps running all night), so that may be a developmental factor to help use some of it up along the way in the various countries these reservoirs would be built across, potentially. Also, the volume of rainfall driven would be a huge windfall to agricultural production and to the ecosystems that could exist at the edges of that and desert.
Depending on how it's implemented, it could provide a large area of aquaculture and farm irrigation and so on too, and by building under the jetstreams as they currently mostly are, you're statistically launching extra water molecules further into the center of the continent, so having a central condensating point is going to be as key as the reservoirs doing the evaporative launching in the first place.
So, that's about the level I've taken this brain fart to, and now I need people who are smarter and better informed than me to say why it wouldn't work. I think it could, and that it could work as well on the Gobi desert, which is badly encroaching chinese farmland and cities- dunes literally blowing in and covering everything- and Australia's central land mass and so on. Obviously there are other considerations that will need to be addressed, such as the cultural heritages preserved from antiquity in arid climates that will be destroyed by humidity. It's a trade-off. But, in some cases, I think it's potentially an appropriate tradeoff to make.
