I’ve often wondered, if we could somehow bring in enough water, could we make vast swaths of desert like the Sahara turn into grasslands and eventually forests?
Has there ever been such an attempt? I mean with so much hunger based on lack of good farmland and many cities in the US like Phoenix and Las Vegas are in the desert, could it be possible?
Well, The Sahara Desert used to be green and lush. Then humans showed up.
So I suppose we could fix it. Wouldn’t be cheat or easy though, and it would be rife with unintended consequences. Just like greening up the desert SW of the US has been.
Egypt thrives because the Nile floods deposit silt along its banks. But the rest of Egypt, the vast majority of it, is still desert.
When even a river the size of the Nile creates no more than a narrow green strip, where would the water to irrigate the Sahara comes from? The Sahara is large as the entire U.S. We use river water to irrigate a tiny fraction of the country and that is already putting enormous pressures on the rivers. There are no rivers feeding in to the rest of the Sahara. Even with imaginary technology, you couldn’t get desalination of the Mediterranean to keep it constantly replenished. And if you put in a million desalination plants, you would need a billion miles of pipeline. And a million miles of roads. And keep everything going in a brutal climate.
Yeah, somebody’s already thought of doing this nonetheless. And the price tag is a mere $2 trillion. Per year. With potentially devastating unintended consequences.
There were proposals to flood only part of the Sahara back in the 19th century, and at a much lower cost than $2trillion. Furthermore, it would be recreating a situation that had existed in historic times, and so would probably be less catastrophic.
The proposal was made by French military officer François Élie Roudaire:
Roudaire’s plan called for flooding that section of the Sahara with salt water from the nearby Mediterranean (which is even saltier than most ocean water), but the claim was that it would moderate the climate, encourage rainfall, and promote trade. Nothing tangible came from the plan, but it later inspired a Jules Verne novel – the last of his published during his lifetime. L’Invasion de la mer ("The Invasion of the Sea) came out in 1905, although it wasn’t translated into English for almost a century.
The climax is an impressive scene of the waters of the Mediterranean rushing in to fill the basin in the Sahara, inundating the Bad Guys the way the Red Sea closed over Pharoah’s forces in Exodus:
It not at all certain how much humans have contributed to this. Natural climate change, driven partly by the Milankovitch Cycle, may be a larger factor. We may have to wait around another 100,000 years to find out.
Besides water, for growing crops you need good soil. The Sahara is a big place with varied conditions. Some places would have soil suitable for crops, some areas would have soils too sandy, or too hard-packed, or too nutrient-poor. (All of which could be remedied, but with a lot more effort and expense than just adding water.) And of course you can’t grow just any plant in just any location–specific plants have specific needs in how much water they need, the temperature ranges they tolerate, how many hours of sunlight a day they need, pH, etc.
Just to correct a misconception in the OP, there is almost no hunger caused by lack of good farmland. There’s plenty of hunger, of course, but it’s caused by people in power in the wrong places who don’t want other people to be fed.
There was the more recent plan to divert excess floodwaters of the Nile to create a second fertile valley from lake Nasser. but apparetly several factors have combined to slow or stop the process. (look for the Toshka lakes on Google maps.) Among other things, the Nile has now been dammed upstream reducing the flow for the next decade…
Similarly, there was like the Algerian suggestion, the idea that the depression east between Siwa and Alexandria, also a hundred feet or more below sea level, could be flooded. unfortunately flooding would create a body of salt water - good for fishing, maybe, and maybe if big enough helping to create a bit more rain in the area - but not making the area sufficiently fertile.
I also used to have a book from the Soviet Union discussing world engineering. One proposal was to dam a spot in the Congo where the Congo river flowed through a valley constriction 3 miles wide. This would create another giant lake in the center of Africa. (I’m sure the locals would be thrilled…) the diverted flow could be used to replenish Lake Chad (which is effectively disappearing since the book was written) and make it even bigger than before. the theory would also be that large bodies of water could alter the rainfall patterns…
Well, you could wait around for a few 10’s of thousands of years…it will bloom again at some point. 
IIRC, it should be going through another wet cycle in 20k years or so.
Sure. As noted, it has gone through several cycles where it is forest and grassland, then desert, then back again. Not sure how ‘we’ could make that happen faster, though I guess if we can get to the point we are doing mega-engineering it’s possible…you just need to figure out how to shift the monsoon rains so that they fall every year in northern Africa instead of central Africa. Should be easy enough. 
Well, hunger isn’t due to lack of available farmland in Africa. But, you mean the whole dessert or parts of it? If parts, then certainly…there is extensive use of fossil water in parts of the Sahara (Libya was doing this a lot in the past…no idea if that’s the case today). So, yeah, it’s possible to use those sources of water deep underground to grow things today. Trouble is, those sources, as in the sources used in a lot of the South West in the US aren’t renewable and can be used up really quickly.
Libya had a project to liberate water in deep underground aquifers under the desert.
It was a huge, long term project, a lot of money was spent on it. Sadly, it was bombed by NATO during the war that overthrew Gadaffi.
My co-worker is Libyan and in fact is in Libya as I type this {he’s a tough old bird}.
He said that the project referred to above is the biggest waste of money the world has ever seen in the context of government projects. {He would know as he personally knew Libyan gov’t ministers}.
Multiple de-salinization plants could have been built close to where the Libyan people actually live, for the cost of that project.
He rants about it every time I bring the subject up. He says Mr. Khaddafi’s other crazy spending projects {of which there were many} pale in comparison. That says something…
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Who controls the spice?
Or to put in another way, food outputs require various inputs. Land is just one of them. As the OP noticed, water is another. So if we have land with no water, if we could somehow add water to the land, we’d have food.
Except that there are lots of other inputs. Fertilizer, sunlight, skilled workers, machinery, transportation, the rule of law, efficient markets, and so on.
Taking water from somewhere and dumping in on some desert land isn’t going to do anything, because the Sahara desert isn’t just lacking in water, it’s lacking in everything. Sure, all that could be developed over time. But if you had a certain inputs, you’d want to allocate them where’d they’d be most effectively used. And so diverting water from one place to another is usually pretty wasteful.
And just plain flat land is not in scarce supply. There are millions of acres of land not being used for agriculture right now, because they aren’t economically viable to farm, because the cost of all the inputs you’d need to farm them would be greater than the value of the agricultural outputs.
One of the Spice girls does. Either Posh Spice, or Muad’Dib Spice.
This was the Qattara Depression Project. It was mainly meant for power generation, as far as I can tell.
Currently the Harkonans