A real-time combination method for the outputs of different rainfall-runoff models

Application of the concept of combining the estimated forecast output of di fferent rainfall-runoff models to yield an overall combined estimated outpu t in the context of real-time river flow forecasting is explored. A Real-Ti me Model Output Combination Method (RTMOCM) is developed, based on the stru cture of the Linear Transfer Function Model (LTFM) and utilizing the concep t of the Weighted Average Method (WAM) for model output combination. A mult iple-input single-output form of the LTFM is utilized in the RTMOCM. This f orm of the LTFM model uses synchronously the daily simulation-mode model-es timated discharge time series of the rainfall-runoff models selected for co mbination, its inherent updating structure being used for providing updated combined discharge forecasts. The RTMOCM is applied to the daily data of f ive catchments, using the simulation-mode estimated discharges of three sel ected rainfall-runoff models, comprising one conceptual model (Soil Moistur e Accounting and Routing Procedure-SMAR) and two black-box models (Linear P erturbation Model-LPM and Linearly-Varying Variable Gain Factor Model-LVGFM ). In order to get an indication of the accuracy of the updated combined di scharge forecasts relative to the updated discharge forecasts of the indivi dual models, the LTFM is also used for updating the simulation-mode dischar ge time series of each of the three individual models. The results reveal t hat the updated combined discharge forecasts provided by the RTMOCM, with p arameters obtained by linear regression, can improve on the updated dischar ge forecasts of the individual rainfall-runoff-models.