The sensitivity to spatial scale of runoff produced by the variable infiltration capacity (VIC) macroscale hydrologic model is investigated by implementing the model over the Columbia and Arkansas-Red River basins at spatial resolutions from one-eighth to 2¿ latitude by longitude. At lower resolutions the meteorological, topographical, and land cover data at the highest spatial resolution are averaged spatially. Simulated mean annual streamflow at lower resolutions is as much as 18 and 12% lower for the Arkansas-Red and Columbia River basins, respectively, as compared to the one-eighth degree implementation. When the VIC model subgrid parameterization for spatial precipitation variability is implemented, the model's sensitivity to spatial scale decreases slightly in the Arkansas-Red River basin, where total runoff at lower resolutions decreases by up to 14% relative to the high-resolution runs. In the Columbia River basin, total runoff is only 4% lower at 2¿ resolution than at one-eighth degree resolution when precipitation variation with elevation is reparameterized at lower resolutions in a manner that replicates mean annual precipitation in the corresponding higher-resolution cells.