 The Soil Wetness Index, SWI, derived from the Advanced Scaterometer, ASCET, Sensor on Board the European Meteorological Operational Satellite, METOP, was tested against the soil moisture temporal pattern derived from a continuous rainfall runoff model, MYSTC. The results showed that the SWI matched the range of variability of the model data, and thus it was successfully assimilated into the model. Three synthetic experiments were conducted to investigate the SWI potential under uncertain conditions. The results revealed that the SWI derived from the ASCET sensor can be used to improve runoff prediction in the study area, especially when initial soil wetness conditions are unknown. This article was authored by Elbraca, F. Maloney, T. Moremarco, and others.