# Reversing the desertification

What will be the effect on a desert-like area if it is covered with millions of umbrella-like structures like the following one?

Would it play any positive role in reversing the desertification?

• had it not been better to use solar panels,the companies setting up solar panels do have some experience in what happens when you cover the ground over a large area. – trond hansen Jun 9 '18 at 14:28
• Deserts are not the result of heat - e.g US Great Basin, for instance, which experiences freezing temperatures in winter. It's the lack of water, either directly (no precipitation), or by the destruction of soils which hold the limited water. – jamesqf Jun 10 '18 at 19:06

It would depend on the reflectivity of the material used - a lighter color will reflect more solar radiation and help cool an area fairly quickly , but it would take longer for the area covered with such structures to experience changes in poleward. energy transport. The poleward heat transport determines where the jet streams are located and how far north and south tropical rains (intertropical convergence zone) move. Thus, whilst the structures would cool the area, there would likely be insufficient rainfall to re-establish substantial plant life and reverse desertification.

In short, because of the need for water and the mesoscale weather patterns in a desert, shading the deserts would have little effect on the rate of desertification.

• there would likely be insufficient rainfall to re-establish substantial plant life and reverse desertification. - is it because of the umbrellas? – user12774 Jun 10 '18 at 8:39
• No, because of how heat is transported from the equator poleward. The equator has surplus heat, which causes are to rise, condense, and rain, that same air then moves away from the equator (near the top of the troposphere) and as it does it cools, at which point it's as far north as about 10-20 degrees where it's lost enough heat energy that it sinks, sinking air doesn't condensate, thus, no rain, and there are semi-permanent areas of high pressure above deserts. That air sinking because it's cooled raises the pressure at the surface. This is shown in this diagram: bit.ly/2Jy5mOx – Phil C Jun 10 '18 at 22:44

Hmm.

Some of this depends on how you view desertificaiton.

A: The arbitrary definition for desert usually is 'an area receiving under 10 inches of precipitation a year" By this definition the arctic is a cold desert, and is very wet.

B: Our mental image of desert is 'hot, dry, sparse vegetation, very sparse habitation'

C: Desertification is usually viewed as a process that changes an arid region to one of deserts. There are various causes of this:

• Overgrazing. Herbivores (goats and sheep often, but also camels, cows...) Reduce the biomass. Because plants aren't transpiring, overall rainfall drops, more clear days means wider temperature swings, harder for plants to get re-established.

• Rain pattern shifts -- either time of year, or prolonged drought.

In the early days of LandSAT, scientists found a perfectly regular pentagon of green vegetation in the sub Sahara. On sending out field agents, they found that some enterprising person had fenced in several square miles of desert scrubland. At the centre was a well. He grazed livestock on each triangle in succession on a 5 year rotation. Because the land had 4 years to recover, it worked.

The well wasn't used to irrigate the fields, but only to supply water for the stock.

One of the potential issues with farming solar power: Solar cells are quite dark, and while some 20% of the energy that hits them is converted to electricity, the rest is converted to heat. The net effect is an decrease in the overall reflectivity, and an overall heating up of the region.

Hot air rises, so now you have a thermal column rising from the solar farm. Depending on local humidity, this can create an overcast layer that interferes with the solar farm. Small units (a mile or do across) won't shade themselves, but really massive farms may create their own interference.

OTOH, some of the ground is shaded, at least part of the day. Lower temps = lower water demand by plants. You may be able to grow plants you otherwise couldn't grow.

On the third hand, if you are close to the sea, it may be possible to harvest that surplus heat to evaporate sea water. This moderates temperatures, but increases humidity. Can you get fresh water out of this?