How did people farm in the desert with oases and underground canals?

People get water in the desert by finding it underground and keeping it there. A green oasis looks like a gift of nature, but most oases, as we know them, are artificial. Water from springs, underground rivers or aquifers can irrigate the surface naturally or through man-made wells, yet continuous human work and know-how are needed to maintain the oasis. In West Asia and North Africa, oases cover about 1,000,000 hectares and support about 10 million people.

The great engineering trick is the qanat. Developed in ancient Iran around 3,000 years ago, it is a gently sloping tunnel, reached through a line of well-like shafts, that taps groundwater, and it carries the water by gravity alone, with no pumps. Because the water travels underground, little is lost to evaporation, even over long distances in a hot, dry climate. Qanats are also resistant to floods and war, and they keep flowing through wet and dry years with only gradual changes.

Skilled workers called muqannis dug them by hand, a job that was handed down from father to son. It was dangerous: if the tunnel's gradient was wrong, the water would not flow or the tunnel would collapse, and misreading the soil could be fatal for the crew.

One qanat in Gonabad, Iran, after 2,700 years still provides water to nearly 40,000 people.