If you use Google Earth to focus on the area north of Riyadh and in the Dawasir valley south-west of the Saudi capital, you will find green circles in the desert. They look a bit like flying saucers that have landed. In fact they are farms, and their peculiar shapes stem from irrigation machines that circle around a hub.

Subsidised agricultural schemes such as these made Saudi Arabia a net wheat exporter early in the 1990s – and added a new dimension to the notion of inefficient allocation of resources.