Integrating geoinformatics and high-resolution soil water retention data for fine-scale desertification sensitivity mapping of the Oued-Sakni sub-catchment, Cheliff-Zahrez hydrographic Basin, Algeria

Introduction This study presents a large-scale, quantitative assessment of desertification sensitivity in the Oued-Sakni sub-catchment (SCOS), a representative unit of the steppe belt of central Algeria. Although the region’s vulnerability to land degradation has been noted in earlier national-scale surveys, its spatial pattern had not previously been mapped at a resolution fine enough to support local management decisions. Methods Geoinformatics and remote-sensing techniques were combined within the MEDALUS (Mediterranean Desertification and Land Use) framework to delineate Environmentally Sensitive Areas (ESAs). The Environmental Sensitivity Area Index (ESAI) was computed as the geometric mean of four thematic indices — the Soil Quality Index (SQI), Climate Quality Index (CQI), Vegetation Quality Index (VQI) and Management Quality Index (MQI) — each built from natural and anthropogenic layers that together describe the land’s susceptibility to degradation. To offset the scarcity of local, high-resolution soil survey data, a methodological adaptation was introduced: soil depth and texture were substituted with high-resolution Volumetric Water Retention (VWR) data drawn from the World Soil Information Service (WoSIS) database. Land cover, the most dynamic of the four inputs, was mapped independently through a Random Forest (RF) classifier trained on Sentinel-2 imagery within Google Earth Engine, achieving an overall accuracy of 86.2% and a Kappa coefficient of 0.823, which gives the vegetation and management layers an empirical grounding rarely available in comparable steppe studies. Results and discussion The results show that the SCOS sub-catchment is highly vulnerable to desertification: critical areas cover 43.6% of the total surface, fragile areas 49.2%, and only 7.2% is classed as potentially sensitive. These figures place the SCOS among the more severely affected steppe catchments reported in the recent regional literature. The resulting ESA maps constitute an operational decision-support tool for prioritizing soil-conservation and rangeland-management interventions in this and comparable semi-arid environments. Prioritizing soil and vegetation conservation in these critical zones is key to protecting forage resources and safeguarding long-term food security.