[ExI] Greening the Sahara

[Dan]

--- On Sun, 7/19/09, Mirco Romanato <painlord2k at libero.it> wrote:
> 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.

I'm not sure that's what would happen -- i.e., that more rain in the Sahara region means less in, say, the Congo region.

> The problem is
> what this would do to other places in Africa.

Or the planet. It's a matter that requires some study, but, again, I'm not sure more rainfall in the Sahara means less rainfall in the rest of Africa or the rest of the globe.

>>> 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,

Well, if you're going to say it's moisture retention, I agree that plays some role, but I think most of the Sahara has very little moisture to begin with. I also think it was lowered temperate that led to decreased rainfall that led to the types of soils and biome we see there now.

> 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.

Oh, no doubt, though if the rainfall were increase, say, to ten times current levels and kept that way for years or decades, I think this outcome would happen "naturally."

> In Amazonia, deforested patches have higher temperatures
> and lower precipitations.

Yeah, but my understanding is these patches are quite small and there are other regional differences.

> More trees cause more rain, not the reverse.

I don't disagree. But if you don't have a certain minimum rainfall, you don't have trees at all -- save for in oasis or near other water sources, no?

> 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.

I don't disagree. Drought is usually the result of what? Reduced 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 flooding last how much? A couple of days? A couple of
> weeks.

As above, I'm not looking for a one time soaking, but changing regional weather patterns over years or decades. (Actually, "permanently" to green the Sahara and keep it green.)

> If you want trees you need water all the year around.
> Better a small quantity always than huge quantities
> rarely.

See above. While that would be better, many areas have seasonal rains and are much greener that the Sahara. In my mind, it'd be easier to alter the rainfall via heating the desert than it would be to engineer year round rainfall.

>>> 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.

This might be true, though it doesn't necessarily mean all quick plans are wrong. The plan I propose might work. There's also a relative problem here. My proposal probably won't work in, say, a year -- save maybe to get some rain NOT to green the desert. It'll probably take several years to get some positive results.

Finally, no reason it can't be coupled with other techniques. Increased rainfall will create a resource that could be use for other greening programs. It's not either/or here, but both/and.
 
> >> 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

All looks good, but I didn't see a clear indication of the costs... Also, without having a good grasp of the costs of my proposal, I'm not sure I could, at this time, make a meaningful comparison. Still, one difference seems to be, magic sand and the like require a lot of infrastructure and it has to be put into place. The darkening to increase temperature might just involve dumping darker material or polluting the area. It might be cheaper and easier to carry out. (One could imagine a two step process: 1. darken and get rainfall increase, 2. use magic sand and similar techniques to hold it.)
 
> > 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.

True, but this would still take a long long time in most of the region, IMO. 
 
> 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.

This sounds good, though with greening the Sahara I'm thinking of enlarging this by perhaps a thousand-fold.
 
Regards,

Dan