The Oued Rheris watershed in southeastern Morocco is highly vulnerable to water erosion and desertification, exacerbated by an arid Saharan climate with low rainfall and rising temperatures. This study aims to analyze the morphometric characteristics of the Oued Rheris watershed to assess its hydrological response time, erosion susceptibility, and sensitivity to desertification, thereby supporting natural resource management and decision-making in at-risk areas. The analysis is based on a 30m resolution ASTER GDEM (Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model) and Geographic Information Systems (GIS) using ArcGIS 10.8 software. Morphometric parameters including drainage density, stream length, compactness index (Kc), equivalent rectangle, Horton index (Kh) were calculated. The basin covers an area of 12,606.7 km² with a perimeter of 687.018 km. The hydrographic network, classified according to Strahler (1957), comprises six orders with a total stream length of 4,412.594 km. The first-order streams dominate (50.16% of total length). The Gravelius compactness coefficient (Kc = 1.71) and Horton index (Kh = 0.46) indicate an elongated shape, approximately seven times longer than wide (length = 300.96 km; width = 41.88 km). The drainage density is 0.35 km/km², reflecting the influence of the basin's geology and arid climate. The elongated morphology of the Oued Rheris watershed implies a prolonged concentration time and attenuated peak flows. However, the low drainage density and arid conditions increase vulnerability to flash floods and sediment transport. These findings are critical for watershed management, soil conservation, and sustainable water resource planning in southeastern Morocco.