Differences in topographic characteristics computed from 100-and 1000-m resolution digital elevation model data

Topographic characteristics computed from 100- and 1000-m resolution digita l elevation model (DEM) data are compared for 50 locations representing var ied terrain in the conterminous USA. The topographic characteristics are th ree parameters used extensively in hydrological research and modelling - sl ope (S), specific catchment area (A(s)) and a wetness index computed as the logarithm of the specific catchment area divided by slope [ln(A(s)/S)]. Sl ope values computed from 1000-m DEMs are smaller than those computed from 1 00-m DEMs; specific catchment area and the wetness index are larger for the 1000-m DEMs compared with the 100-m DEMs. Most of the differences between the 100- and 1000-m resolution DEMs can be attributed to terrain-discretiza tion effects in the computation of the topographic characteristics and are not the result of smoothing or loss of terrain detail in the coarse data. I n general, the terrain-discretization effects are greatest on flat terrain with long length-scale features, and the smoothing effects are greatest on steep terrain with short length-scale features. For the most part, the diff erences in the average values of the topographic characteristics computed f rom 100- and 1000-m resolution DEMs are predictable; that is, biases in the mean values for the characteristics computed from a 1000-m DEM can be corr ected with simple linear equations. Copyright (C) 2000 John Wiley & Sons, L td.