Operational flood forecasting on the River Meuse in Belgium is based on both hydrologic and hydraulic modelling. The hydrologic models take into account the rainfall-runoff relationships for the main subcatchments. This allows to handle the spatially-variable hydrologic behaviour of the total basin. Classical modelling procedures such as a time-invariant stochastic approach, cannot handle problems related to the changing dynamics of the hydrologic processes. This paper discusses a methodology based on on-line estimation of parameters, to model short variations in the response of the main subcatchments of the Meuse. The variation of the parameters is modelled by means of a random walk method. Some objective criteria for evaluation forecasting performance are introduced. It can be concluded that, in general, adaptive modelling improves the real-time performance within the linear framework.