[ExI] Greening the Sahara

[Dan]

--- On Thu, 7/16/09, Mirco Romanato <painlord2k at libero.it> wrote:
> Dan ha scritto:
> > Any ideas on how to do this?
> > 
> > An idea I had was to cover strategic swaths of it with
> dark material,
> > thereby causing its daytime temperature to rise
> causing the air to
> > rise faster pulling in more moist air from the costs.
> Once rainfall
> > is higher, it seems the greening would take care of
> itself.
> > 
> > Any thoughts on this?
> 
> It would raise the temperature locally, big time. Killing
> the life there.

I disagree. The temperature would rise locally, but that would start or increase the regional convection cycle, pulling in cooler moist air from the Atlantic, Mediterranean, and perhaps the rest of Africa. The average temperature would likely rise, but given higher percipitation, the daily high temperature might fall.

And I'm not talking about making the surface temperature 200 degrees Celsius. I think a five degree rise would do the trick, but I don't have a precise model to determine what's needed here.

> The best way to green the desert is to plant trees, many
> trees.

Given current trees, hard to solve this problem without lots of rainfall.

> The biggest problem is to keep the water from sinking down,
> becoming
> unavailable or washing up salt poisoning the terrain.
> The solution is hydrophobic sands.

I thought, given that any rainfall tends to actually cause huge flooding, that the problem is water doesn't usually stay there, but rushes away. Granted, it's a very rare occurence in the first place, but I'm not sure the problem is whatever rain comes all sinks into the ground.

> The plan is simple, and locals already do it with low
> technology around their orchards.

Too small scale to regreen the whole desert quickly.
 
> The sands is not so costly, so it is possible to deploy it
> and profit of
> the new terrain available for agriculture.
> The hydrophobic sand can be packed inside a tape-like
> structure and
> deployed 2-3 meters under the terrain. Then, all the water
> will stay
> near the surface and will be available to the plants
> roots.

It's a nice idea, but I'd have to see the costs.
 
> Planting trees and letting them grow will provide a cover
> of the
> terrain, that will reduce the evaporation and the
> temperature at the
> ground level.
> 
> This need to start around existing oasis and water bodies
> and grow from
> there.

Well, if that were the plan, yes. You'd still need a means of drawing a lot more water -- probably by means of rain -- in. Without that, you'd probably have larger and more oases, but it'd still mostly be desert.

Regards,

Dan