The Inca were at this sort of thing as well. This illustration from wiki is similar to the one in the video in having a circular depression at the bottom.https://en.wikipedia.org/wiki/Incan_agriculture
And confirming Mr Harper's theory of desertification and where does rain actually come from we have this statement.
' Hiram Bingham, the American explorer who found the ruins of Machu Picchu in 1911, wrote:
No less striking than the remarkable system of highways were the irrigation ditches which ran for scores of miles in the Central Andes. The height of the mountains, often rising to 18,000 or 20,000 feet, forces the moisture-laden winds coming from the east across the humid basin of the Amazon to deposit their burden in heavy rains on the eastern slopes of the great Andean chain. Little rain ever falls on the western slopes. On fact, one of the greatest deserts in the world is the two-thousand-mile coastal strip extending from central Chile to Ecuador.'
Taken from - http://incas.homestead.com/inca_irrigat ... achay.html