ABSTRACT Hydrology has important contributions to make to the development of global models by providing independent calibration of land surface components of global circulation models (GCMs), by validation of GCM outputs at the basin level through comparison of recorded and simulated streamflows and by examining the implications of climatic change scenarios on water resources. Most importantly, hydrological models are necessary to provide the lateral links needed to close the land surface/boundary layer feedback loops. At grid scales, lateral water fluxes significantly affect soil moisture availability for evapotranspiration. At regional scales, accumulated runoff determines the freshwater inflows to the oceans which drives the sea-ice cover and ocean salinity flows. A hierarchy of hydrological models (HHM) has been developed using a ‘grouped response unit’ (GRU) approach to link process parameters to land cover, basin topography and the areal extent of climatological phenomena. The GRU allows land-use/land-cover to vary from element to element within a unit. Analyses of data suggest a grid element in the order of 10 km × 10 km is appropriate for hydrological modelling. Temporal resolution is accommodated by using three hydrological models operating at hourly, daily and monthly time scales.