Many modern methods of agriculture require some form of irrigation in order to meet the needs of an increasing population. One method is called centre pivot irrigation. Water is pumped from a depth of up to 1km to the surface and distributed via a large centre pivot irrigation feed (Figure 1). The large circular fields can vary from a few hundred metres to as much as 3km in diameter. In order for them to function, the terrain needs to be reasonably flat, so archaeological sites are usually cleared to make way for the plants. DigitalGlobe satellite images, viewed on Google Earth, show the increase in the centre pivot irrigated fields of Saudi Arabia between January 2000 and February 2015. The number of irrigated areas has more than doubled.
The threat posed to archaeological sites can be seen in Figure 2 (below) of a desert kite (marked in red) near Azraq (the stone walls radiating from the oval structure on the right) in October 2003 and June 2013. Kites are long dry-stone walls converging on a neck that opens into a confined space, and are used for hunting wild animals. There are a number of other small circular enclosures around the kite that are not marked.
Figure 1 (left): Centre pivot irrigation at Jubbah Oasis, southern Nefud, Saudi Arabia. Copyright Richard Jennings, Palaeodeserts Project.
Figure 2 (below): Encroachment of centre pivot irrigation upon deserts kits near Azraq, Saudi Arabia. See also NASA’s recent image of the day – crop circles in the desert – for other examples see here.