[ExI] Greening the Sahara

[Mirco Romanato]

Dan ha scritto:
> --- On Thu, 7/16/09, Mirco Romanato <painlord2k at libero.it> wrote:

> 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.

You want move the monsoon up to the desert. The problem is what this
would do to other places in Africa.


>> 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 real problem is not rainfall,

>> Border zones on the north and south, where the desert merges with 
>> the steppe, receive about 10 in. (25 cm) of rain a year with some 
>> seasonal regularity, but over most of the region rainfall is 
>> sparser, with an average annual total of less than 5 in. (12.7 cm);
>>  rainfall is usually torrential when it occurs after long dry 
>> periods that sometimes last for years.

but keeping the water available, reducing the evaporation, reducing the
local temperature (shadows) and keeping the soil there and the wind from
taking it away.
In Amazonia, deforested patches have higher temperatures and lower
precipitations. More trees cause more rain, not the reverse.
Drought in Africa and Amazonia, usually let the soil to be exposed to
the Sun and the winds and the thin fertile layer is removed, leaving
barren sand and rock.


>> 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 flooding last how much? A couple of days? A couple of weeks.
If you want trees you need water all the year around.
Better a small quantity always than huge quantities rarely.


>> The plan is simple, and locals already do it with low technology 
>> around their orchards.
> Too small scale to regreen the whole desert quickly.

This is a problem with western people.
We like results quickly.
So we fall for solutions that are quick, not for solutions that are
right. Then the "quick" solutions fail in the long terms, but our
attention span is too short to note it.

>> 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.

http://nextbigfuture.com/2009/02/hydrophobic-sand-details-waterproof.html
http://nextbigfuture.com/2009/02/waterproof-sand-could-green-deserts.html
http://www.dimecreations.com/home.html

http://en.wikipedia.org/wiki/Magic_sand

http://www.dimecreations.com/home.html

>> 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.

What it is needed is to use better the available water, then instead of
a negative balance of water, you have a positive one (locally). Then
enlarge "locally" as you have more water available.


Citing Brian Wang:
>> As noted in a previous article about greening deserts 75% of the 
>> water for irrigation can be saved using the nanosand and 85% of
>> water in the middle east and north africa is used for irrigation.

So, using the nanosand it is possible to enlarge 4 time the land irrigated.

>> By simply laying down a 10-centimetre blanket of DIME Hydrophobic
>> Materials sand beneath typical desert topsoils, the new super sand
>> stops water below the roots level of the plants and maintains a
>> water table, giving greenery a constant water supply. 3000 tons/day
>> is already being produced. 1 ton of silicate coated sand would
>> probably be good for 10 square meters. 4 days of production to
>> cover one square kilometer. More factories will be needed made to
>> scale this up to address the water crisis in the Middle East,
>> Africa, India and China.

Mirco