Spatially uniform specific discharge from headwater to river basins on the Chinese Loess Plateau

Although there is a general consensus that spatial heterogeneity is ubiquitous in hydrological responses, it is common practice to assume a constant specific discharge among nearby catchments. This study addressed the contradiction in a similar to 18,000-km(2) loess area of the Chinese Loess Plateau using 11-year streamflow records at 16 streamflow gauging stations. The studied watersheds were intensively cultivated during the observational period but human regulation such as dams, irrigation, and diversions, was scarce. Results show that the high spatial variability observed at the intra-annual scale was smoothed out such that the specific discharges of total streamflow, baseflow, and surface flow at multi-annual scales were fairly uniform among the studied watersheds. As a result, a direct scale extrapolation was applicable across four orders of magnitude in drainage area sizes (from 0.107 to 3,893 km(2)); meanwhile, a constant would suffice for spatial predictions of the mean annual specific discharge with a moderate predictive error of similar to 13%, showing that a larger catchment is hydrologically the sum of its smaller catchments in the homogenous loess landscape.