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Make the Sahara Green Again!

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...or maybe not. 


A future megaproject that fascinates me is using geoengineering to green the Sahara Desert. The Desert has always seemed like a huge waste of space that should be put to productive use. 


In another topic, I described how one aspect of such a megaproject could be using desalinated seawater to fill parts of the Sahara that are below sea level: 



I'm reminded of the Qattara Depression Project: https://en.wikipedia...ression_Project


Here's my variation on the idea: 


1) A conventional Generation 2 nuclear fission reactor is built at El Alamein. It generates electricity, but also desalinates seawater from the Mediterranean by using seawater as coolant. (The big question mark is what to do with all the salt) 


2) The freshwater produced by the reactor is pumped through aqueducts that lead southward to the Qattara Depression. The aqueduct has several small dams that generate electricity as the water flows downhill. 


3) At the end, the water flows into the Depression. The flow rate is controlled so that the Depression partly fills up until the evaporation rate equals the liquid inflow rate. 


4) The evaporated water would, presumably, hopefully, condense into clouds and lead to local rainfall, which would green that part of the Sahara. Salt-tolerant plants could be introduced at the edges of the lake, perhaps along with advanced greenhouses. 


This setup could be used elsewhere in the Sahara, where there are other depressions. 




A related project would be diverting water from rainforest rivers in Central Africa to refill Lake Chad in the arid Sahel region. Thousands of years ago, the Sahel's climate was wetter, and the Lake was much larger as a result. So much so that scientists today call its former state "Lake Mega Chad." The Lake has steadily shrunk, mostly due to natural climate changes, but now also thanks to human-induced ones, and it's at risk of disappearing, which will make the region around it drier as well. 




There are two, proposed water diversion projects that would keep Lake Chad from drying up. One, called the "Transaqua Transfer Scheme," is expensive and involves building several dams and a long canal in the DRC and Central African Republic. The other, called the "Inter-Basin Water Transfer," is cheaper and merely involves building pumping stations and water pipelines in the CAR. It would be solar-powered. 





There are other extinct mega lakes in the Sahara that could also theoretically be refilled, but it would clearly be more expensive and technically challenging given their longer distances from freshwater sources like the Congo Basin: 




The projects to fill depressions and extinct mega lakes would be a great start, and would help green the regions surrounding them, but much more would be needed to transform the rest of the massive Sahara Desert. This video explores the feasibility of using massive solar panel farms and wind turbine farms to generate energy and make the Desert's climate more clement (cooler, less windy, and more rainy):



His analysis focuses on covering all 9.2 million sq km of the current Sahara Desert in solar panels. However, if the inland lakes and depressions are filled in with water, the Desert's land area will be reduced. Additional land area surrounding those bodies of water will also be set aside for rewilding (planting trees and introducing animals, kind of like terraforming), further reducing the area that should be covered in solar panels. Finally, I doubt the entire remaining portion of the Desert will need to be covered in solar panels to substantially cool it down. Just as the "heat island effect" heats up whole cities, a "solar panel island effect" could cool down the Desert a lot, even if there were still large open spaces of sand with nothing above it. All of these factors mean we'll need to cover much less than all 9.2 million sq km of the Sahara Desert with solar panels to transform at least large portions of it into savannah, where plants, animals and humans could live. 


Of course, the video analysis raises important problems with such a megaproject. His calculations regarding the amount of metal, glass and plastic needed to make that many panels show that it would take many years' worth of global production. Refilling Lake Chad would also reduce the size of trans-Atlantic dust storms that fertilize the Amazon rainforest with nutrients (greening the Sahara would mean de-greening the Amazon; some portion of the western Sahara should probably be left as desert to maintain the dust storms). Additionally, filling the lakes and depressions with water would be politically infeasible given the lack of money for such projects in Africa, as well as the corruption of their politicians and lack of cooperation between key neighboring countries.  


With that in mind, I don't think the constellation of megaprojects needed to green the Sahara Desert will be completed...until some time after AGIs have taken over the planet, erased Africa's political borders, and have the industrial capacity to make several times more metal, glass, and plastic than we humans can under our pitiful, eight-hour factory work days. 




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This guy is skeptical of the project's value: 

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