Digital Elevation Models are commonly used to hydrological features extraction to feed distributed models. One of the first steps for this data acquisition is the choice of the threshold area needed for stream initiation definition. For three French Mediterranean catchments of almost 50 km2 these thresholds were tested. Based on previous results, it was retained 7 proportions of the catchments for these thresholds to analyze the influence over the SCS-CN model ability to calculate the effective precipitation. Calculations have been done using a SPOT4 image interpretation resampled to 50m-grid resolution and the CORINE Land Cover map of the region. For any event, any catchment and for both land cover classifications, the effective precipitation estimation does not depend on the threshold choice until breaks. These breaks correspond to surface thresholds of 1 km2 and 6 km2 (ie around 2% and 10% of the total surface). The paper contributes to proposing assumptions on the relationships between surface thresholds and land cover / land use descriptions.