The objective of this study was to simulate the evolution of soil erosion in a semi-arid mountainous watershed (225 km2, High Atlas Mountains, Morocco) under different scenarios of climate and land use change to the end of 21st century. Erosion plots monitored over four years showed spatially contrasted results. Most of the soils produced from 0.015 to 2.5 t/ha/y, whereas badlands produced 350 t/ha/y The average sediment yield measured at the outlet during the same period was approximately 4 t/ha/y. The STREAM distributed erosion model was parameterized using these field measurements (infiltration rates and runoff sediment concentrations). The results showed an overall agreement between the modelled and measured annual cumulative sediment yields. Simulations of the ARPEGE meteorological model were used for the 1960-1990 and 2070-2100 periods. The changes between these two periods were downscaled using three different methods, decreasing annual precipitations by 10-14%, although with more rainfall in summer and fall. Climate change alone increased sediment yield by 4.7-10.1%. However, simulations showed that land use changes might potentially induce much larger changes in erosion (up to 250%), approximately proportional to the evolution of the extension of badlands.