(phone +33 1 64 15 36 48; fax 7 +33 1 64 15 37 64) 8 9 Abstract 10 In this paper we suggest to innovatively use scaling laws and more specifically 11 Universal Multifractals (UM) to analyse simulated surface runoff and compare the retrieved 12 scaling features with the rainfall ones. The methodology is tested on a 3 km 2 semi-urbanised 13 with a steep slope study area located in the Paris area along the Bièvre River. First Multi-14 Hydro, a fully distributed model is validated on this catchment for four rainfall events 15 measured with the help of a C-band radar. The uncertainty associated with small scale 16 unmeasured rainfall, i.e. occurring below the 1km x 1km x 5min observation scale, is 17 quantified with the help of stochastic downscaled rainfall fields. It is rather significant for 18 simulated flow and more limited on overland water depth for these rainfall events. Overland 19 depth is found to exhibit a scaling behaviour over small scales (10 m-80 m) which can be 20 related to fractal features of the sewer network. No direct and obvious dependency between 21 the overland depth multifractal features (quality of the scaling and UM parameters) and the 22 rainfall ones was found. 23