General circulation models (GCMs) currently perform vertical water and energy balances at 20- or 30-min time intervals for grid points 2¿-4¿ apart but generally contain no information on the land-phase transfer of water between grid points or within watersheds. As a result, they operate on an incomplete hydrological cycle. This study combines a hydrological model with a GCM for a macroscale watershed. A water balance was carried out at 12-hour time intervals for a 10-year period using the Canadian Climate Centre GCM II data set for grid points within and surrounding the 1.6¿106 km2 Mackenzie River Basin in northwestern Canada. The water surpluses from each relevant grid point were accumulated to provide a simulated hydrograph at the outlet of the Mackenzie River. A hydrological model was calibrated and verified using 5 years of recorded climatological and hydrometric data as well as land cover data from classified National Oceanic and Atmospheric Administration advanced very high resolution radiometer images. The climatological outputs from the GCM (precipitation, temperature, and evaporation) were then used as inputs to the hydrological model, generating a second hydrograph for the Mackenzie River. The results show that using the hydrological model with the GCM data produces a better representation of the recorded flow regime. The study provides a means of verifying the performance of the GCM and is a first step in developing a continental-scale hydrological model which will, ultimately, form a part of a full model of the global hydrological cycle. ¿ American Geophysical Union 1994