A large-scale grid-based hydrological model of the Severn and Thames catchments

This paper addresses the issues of scale and appropriate model complexity for large-scale hydrological models. A grid-based hydrological model, which employs the UK Meteorological Office: Rainfall and Evaporation Calculation System, is applied to the Severn and Thames reproduce the observed mean annual runoff over a 10-year period to within 6% with no prior calibration. The variation in the model performance is strongly correlated with the linearity of the annual rainfall/runoff relationship and a climate index. At the monthly scale, runoff routing becomes significant, and the introduction of a two-parameter routeing algorithm significantly improves the monthly runoff simulations giving efficiencies of 90% and 88% for the Severn and. Thames respectively The results provide guidance to climate modellers looking for efficient and robust land-surface parameterizations, and indicate the potential application. of such a modelling scheme to water resource managers.