 The study evaluates the effectiveness of using satellite-derived soil moisture estimates to improve flood estimation in the Upper Tiber River Basin, in central Italy. The advanced SC8 Arometer, ASCOT, sensor on board the METOP satellite was used to derive the Soil Wetness Index, SWI. The SWI was compared with modeled data from a continuous rainfall runoff model, MISDC, and then assimilated into the model using a simple data assimilation technique. Three synthetic experiments were conducted to investigate the potential of the SWI when uncertain conditions occur. Results show that the SWI can improve runoff prediction in the study area, particularly when initial soil wetness conditions are unknown. This article was authored by El Braca, F Maloney, T Moremarco, and others.