Too little water, everything dies; too much, it drowns. In Guyana, the problem for farmers has often managing the country's vast reserves of water; draining swamps, maintaining channels; stabilising the watertable.
For the Portuguese immigrants, these were unfamiliar problems. Back on Madeira, the problem was - and is - one of scarcity, or, rather, redircting precious water. Up in the mountains, you still come across the remarkable network of irrigation channels (levadas) that bring water from the wet north side of the island to the dry, fertile south side. The technology is essentially Arab in origin (I've seen similar systems in Morocco and Libya) but in Madeira it is extremely impressive; the network of channels is thought to extend almost 2,000km. Each channel is around 15cm deep, and some drop only a few centimetres per kilometre. Their construction spans several hundred years (and they are still essential to the island's agriculture). The one in the photo was built in 1835, using slave labour.
About 20% of the levadas are walkable. As they follow the contours , the walking is easy. Easy, that is, in terms of gradient. In many parts however, the path is only a few inches wide, and the cliffs then drop away hundreds of feet. I often found myself crawling along, on all fours ... Spare a thought for the original