It’s an interesting concept that you raised. The scheme as proposed may not be all that viable but with some adaptations it could have merit.
There would be many problems associated with constructing canals, not least of which is the fact that the Sahara isn’t particularly flat. Some quite sizeable sections are below sea-levels but in other places the elevations exceed 3,000m.
We often think of the Sahara as being an endless sea of sand dunes. There certainly are plenty of dunes but actually most of the Sahara is a large and relatively flat expanse of loose gravel and small pebbles.
The ground would make it hard to construct canals. When we construct a canal it’s usually a case of excavating a channel through the ground and lining it with an impermeable membrane, such as clay, in order to retain the water. In the Sahara the ground is unstable, a sizeable excavation would be required which would need to be lined with thick concrete walls and base; not only to retain the water but to create a structurally rigid channel. This would be a massive engineering project, even if completely level ground could be found.
In areas of sand the dunes are constantly shifting. You may have heard reference to “singing sands”, this is the sound made when wind sets up a harmonic frequency within the sand-dunes as it blows them along. If you were able to view some aerial time-lapse photography you’d see sand-dunes moving across the desert. This would cause a problem for any canals that got in the way.
Another problem is one of scale. The air around you will contain quite a bit of water vapour, if you’re in an average sized room (5 x 5 x 2.5m) then there’s typically enough water in the air to fill 35 kettles (up to 140 if it’s very hot and humid). This water doesn’t fall as rain because there’s enough air and heat to keep the water vapour aloft and in the form of a gas.
To get it to rain you have to exceed the amount of water vapour the atmosphere can hold, something known as the saturation vapour point. When SVP is reached the air has to get rid of excess moisture which it does by condensing as dew on surfaces or via precipitation.
The temperature in the Sahara fluctuates greatly, very hot during the day but cold at night. All the same, even in the cold night you’d still need about 1kg of water vapour in every cubic metre of air before it started raining. This means that in an area measuring just one cubic kilometre (about a quarter of a cubic mile), you’d need a million tonnes of water vapour. Unfortunately, the amount of evapouration from the canals wouldn’t come close to this.
But what about something bigger than canals? What about creating a lake instead? This could be done in one of the areas that’s below sea-level, then it’s just a case of constructing a canal to the nearest sea and the water would flow into the lake from where it would evapourate.
One problem though, the salt would get left behind and in time the newly created lake would become a salt-pan. To prevent that happening the lake would need an outflow; it would need water running into it, and out of it, so as to flush out the salt. But this wouldn’t work if the lake were below sea-level, and water wouldn’t flow into it if it were above sea level.
To make the scheme viable it would have to be done on a small scale, and around the edges of the Sahara where water could more easily be pumped in/out.
So what about the effects on the climate. In places where there is a constant supply of water vapour, such as evapotranspiration from forests or evapouration from oceans, the climates tend to be both cooler and wetter; the water vapour in the air absorbs some of the heat energy so cooling the air. The moist air is carried by the prevailing winds and as it cools some of that moisture is precipitated out.
Where such conditions exist on a large scale, such as the Amazon rainforest, the weather can be affected up to 1,000km away, although most of the influence is much closer to the source. This is one reason why it’s so wet in rainforest areas – it’s the same water being cycled round and round.
Because a desert hydration scheme would be small-scale, the effects on the climate would only be noticeable close to the scheme itself. It’s unlikely there would be sufficient evapouration to cause any real change to rainfall levels (what water did evapourate would be dispersed into the atmosphere and carried away). The most noticeable effects would be a local increase in humidity and a decrease in temperatures and this would favour some species of fauna and flora.
Digging a channel 100 feet wide and 30 feet deep across the the Sahara to the Mediterranean to bring you saltwater is a good idea. If you do this, I'll give you my Freshwater solution. I have a Global ocean operation running now telling all continents people to lower all rivers 40 feet deeper that lead to the oceans, so all rivers will stay in tact, but if you dig your channel as I suggested, then my 2nd Phase will drop to 3 continents. This will work for you and the rest of our planet, so go right ahead, but make it 100 feet wide and 30 feet deep, so you'll have more fish from the oceans, since they've been breeding for 34 years. Good Luck. Global Command
The thought is to increase the humidity of the air in hopes of bringing rain. Also there are many plants that grow well soil near salt water or even in salt water marshes. I was wondering if people thought such an idea was viable for changing the climate of the Sahara, possibly making it green once again. And if did change the climate what effects it might have more globally.
I expect salt from the water would be a problem as others say.
To see the effect we can look at what happened since building the Suez canal what affect it had on the nearby land. Is the 'soil' by the canal wet, marshy or dry? How wide is the strip affected? What plants grow there? Any trees? Is the air more humid and does this bring salt causing any harm? Can crops be grown? Does anyone use canal water for irrigation?
The water would evaporate, then you would have a lot of salt. A similar occurrence is when a land mass was next to the ocean and a mountain range rose and isolated it from the sea. It is now called the Great Salt Lake in the USA. Only it is resupplied with fresh water from the nearby mountains, still it is not productive.
The sea water would poison the soil with the salt making it impossible to grow anything with it anyway. So why bother? You need fresh water to grow crops.
It was proposed a long time ago http://r.search.yahoo.com/_ylt=A0SO8wbDp...
