Passive Desalination with photovoltaic pumping

[kandrathe]

I'm no engineer, but I've always wondered why large-scale desalination isn't the obvious solution to fresh water shortages, especially on the coasts.

Yes, me as well. I wonder why North Africa couldn't use it's solar power to reclaim parts of the Sahara from west to east, increasing the relative humidity of the entire region.

Well, the issue with the Sahara is due to the change in tilt of the Earth that occurred 25k years ago. Prior to that the Sahara was very lush, but after the change in tilt, the desert grew.

Another aspect is that ancient man unknowingly caused some deserts to grow due to irrigation with sea water. A prime example of this is the growth of the Arabian desert. At one time, probably close to 6k AD, people started irrigating parts of Arabia using waters from the Persian Gulf, Red Sea, and Arabian Sea and this salted the earth there and destroyed the arable lands there thus causing the desert to grow to its present state.

Interesting. I've heard that even the Sphinx in Egypt was originally eroded by water, not sand.

Humans are also not helping ... explanation by a Namibian... "There are many factors at play, but it appears that the most important reason is the desertification of the Sahel, South of the Sahara. This semi-arid region used to grazed by livestock only during the rainy season, because there was no drinking water during the dry season (the nomadic livestock farmers would trek to the Southern, high-rainfall agricultural areas in the dry season where they would graze on the crop left-over material after the harvest season, simultaneously fertilising the fields). The crop farmers in the South changed their crops to cash crops with later and longer harvest seasons (and little to eat for the livestock) while in the Sahel, more and more boreholes were drilled in order to provide the livestock with permanent drinking water throughout the year. Due to the piosphere effect around the water points where the veld no longer had any rest period, but were being continually grazed and trampled throughout the year, the top soil, without any vegetative cover, is being removed by wind… the effect is first circles of desertification around the permanent water points that increasingly become larger (as the livestock graze further away in order to get enough food) until it forms continuous areas of desert, joining the Sahara to the North. This effect is exacerbated by periodic droughts."