Shapes of the water: the rectangle and the circle. A tentative survey on irrigation in the Sahel

This chapter explores the two patterns with which different irrigation systems “draw” spaces in the Sahel: rectangles and circles. The two outcomes depend on the different irrigation methods. In the first case, the rectangles are derived from the orthogonal grid of irrigation channels in those systems that distribute water by gravity into the fields from reservoirs or pumping systems. In the other case, the circles are formed by central pivot irrigation systems. Using remote sensing techniques and the Google Earth Engine (GEE) platform, we identify and monitor these irrigation systems, employing open-source geographic information system (GIS) software to process the data. Our analysis covers the period from 2000 to 2024 for pivot systems and from 2016 to 2024 for surface irrigation systems, using Landsat and Sentinel satellite imagery, respectively.