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Sheep and goat production is the main and sometimes only agricultural activity available to populations living on rangelands in the arid regions around the Mediterranean. Desertification threatens large areas of Mediterranean arid rangelands but remains difficult to describe, quantify and accurately locate for management purposes. A methodology is described which estimates a Spatial Rain-Use Efficiency Index (SRUEI) and its potential use to evaluate rangeland condition at a large scale. It is based on an Aboveground Net Primary Production (AGNPP) map generated from field herbage mass measurements and a rainfall spatial distribution map derived from local elevation-rainfall gradients with the whole resulting from satellite imagery processing and GIS technology. The area of the case study was in the Nâama-Mecheria region located on the High Plateau south of Oran (Algeria). It covers ~215000ha, receiving ~200mmyear-1 of winter and spring precipitation. The Nâama-Mecheria SRUEI-derived map clearly shows the degradation gradient declining away from the settlements. The Mecheria AGNPP 2007 map and associated grazing rings indicate that the Mecheria cooperative flocks may ingest 48-57% (Range Use Factor) of the rangeland's seasonal plant production, which is barely compatible with sustainable rangeland use. When adding the effect of fuel wood collection by local residents and rain-fed arable cropping, the Nâama-Mecheria region is undoubtedly heading towards a slow but certain desertification of its fragile arid rangelands unless correcting measures are implemented. The SRUEI and associated results are powerful tools that allow rangeland conditions to be mapped, and which can be employed in planning and pursuing sustainable management of rangelands in such arid areas.