[[a cross-post of my comment from the Lesswrong cross-post of the original post, in that thread of comments!]]
Let’s start at a more practical scale: make the Negev Bloom.
The Negev is 12,000 km2, which, if we want grasslands, needs some 300mm extra rain or more each year. That’s 3.6 billion tons per year, or just 10Mt a day. With 20g/m3 humidity, we’ll need passage of 500 billion m3 of air-flow each day. With convection driven by solar concentrators (those same which drive the pumps) to increase wind velocity during the day to 4m/s, across trays stacked 12.5m high, provides 50m3/sec, 4.32 million m3 per day across each meter of intake.
Next, we pump rows inland, as each humid layer rises, to capture drier air as they mix and move-past. Additional solar concentrators power these, and conveniently, the concentrators’ intense heat pushes humid air higher than it would during gentle billowing convection, rising to cool & enter the cloud-cycle faster. We would only be prevented from extending more rows if the elevation rises too high, or we create so much humidity and cloud-cover that our solar concentrators cease. Let’s just say we have four rows.
With 4.32 million m3 per meter of intake width, we’ll need 116,000 meters… that’s only 72 miles. With our four rows, that’s a length of coast 18 miles long. The Gaza Strip is enough to water the Negev.
And, as I mentioned in an earlier response to you, the vast majority of the humidity released by the Persian Gulf, Dead Sea, Red Sea, Mediterranean, is being used to fight-against the immense downdraft of adiabatically-heated and ultra-dry upper atmosphere, which is descending because of the boundary between Hadley and Ferrel cells. So, yes, there are billions of tons of water evaporating, and no rain!
Yet, we know from geological records as recent as 9,000 bc, the Sahara was wet, with vast lakes—because of a slight increase in humidity above the threshold for accumulation. The deserts are not ‘infinitely’ dry, such that all water never results in rain. Rather, they are just below a ‘threshold’, with water added by evaporation in huge amounts, and a slightly huger amount being taken away by adiabatic downdraft. If we add just a portion of humidity, we are doing exactly what occurred across the Sahara repeatedly, and it led to accumulation, because it was enough to cross the desiccation threshold. Our own soil records prove that the desert can be green, with just a little more water than it currently evaporates.
These details might help see the complexities
[[a cross-post of my comment from the Lesswrong cross-post of the original post, in that thread of comments!]]
Let’s start at a more practical scale: make the Negev Bloom.
The Negev is 12,000 km2, which, if we want grasslands, needs some 300mm extra rain or more each year. That’s 3.6 billion tons per year, or just 10Mt a day. With 20g/m3 humidity, we’ll need passage of 500 billion m3 of air-flow each day. With convection driven by solar concentrators (those same which drive the pumps) to increase wind velocity during the day to 4m/s, across trays stacked 12.5m high, provides 50m3/sec, 4.32 million m3 per day across each meter of intake.
Next, we pump rows inland, as each humid layer rises, to capture drier air as they mix and move-past. Additional solar concentrators power these, and conveniently, the concentrators’ intense heat pushes humid air higher than it would during gentle billowing convection, rising to cool & enter the cloud-cycle faster. We would only be prevented from extending more rows if the elevation rises too high, or we create so much humidity and cloud-cover that our solar concentrators cease. Let’s just say we have four rows.
With 4.32 million m3 per meter of intake width, we’ll need 116,000 meters… that’s only 72 miles. With our four rows, that’s a length of coast 18 miles long. The Gaza Strip is enough to water the Negev.
And, as I mentioned in an earlier response to you, the vast majority of the humidity released by the Persian Gulf, Dead Sea, Red Sea, Mediterranean, is being used to fight-against the immense downdraft of adiabatically-heated and ultra-dry upper atmosphere, which is descending because of the boundary between Hadley and Ferrel cells. So, yes, there are billions of tons of water evaporating, and no rain!
Yet, we know from geological records as recent as 9,000 bc, the Sahara was wet, with vast lakes—because of a slight increase in humidity above the threshold for accumulation. The deserts are not ‘infinitely’ dry, such that all water never results in rain. Rather, they are just below a ‘threshold’, with water added by evaporation in huge amounts, and a slightly huger amount being taken away by adiabatic downdraft. If we add just a portion of humidity, we are doing exactly what occurred across the Sahara repeatedly, and it led to accumulation, because it was enough to cross the desiccation threshold. Our own soil records prove that the desert can be green, with just a little more water than it currently evaporates.