Evaluating spatial variability and scale effects on hydrologic processes in a midsize river basin

The impact of spatial variability and scale on the dynamics of hydrologic processes in the Monongahela river basin of USA was investigated using a physically based spatially distributed hydrologic model developed by Yildiz (2001). The hydrologic model simulations were performed at 1 and 5 km spatial scales for a 5 month period from April through August of 1993. Effects of spatial variability in topography, vegetation and hydrogeology and of spatial scale were evaluated through comparisons of the simulated and observed streamflows for the prescribed resolutions at different locations across the river basin. The evaluation of observed and simulated streamflows using the statistical measures of mean, standard deviation, coefficient of variation, root mean square error and bias showed that model statistics of streamflow followed closely the spatial patterns of those of existing observations, that is, the model captured the space-time features of the 1993 flood across the basin. The changes in the nature of the rainfall-runoff response due to changes in the spatial resolution of the model indicated that there was also a change in governing physical processes at different resolutions. Here, this change was expressed in terms of the relative contributions of surface and subsurface flows.