Effect of Uncertainty of Grid DEM on TOPMODEL: Evaluation and Analysis

TOPMODEL, a semi-distributed hydrological model, has been widely used. In the process of simulation of the model, Digital Elevation Model (DEM) is used to provide the input data, such as topographic index and distance to the drainage outlet; thus DEM plays an important role in TOPMODEL. This study aims at examining the impacts of DEM uncertainty on the simulation results of TOPMODEL. In this paper, the effects were evaluated mainly from quantitative and qualitative aspects. Firstly, DEM uncertainty was simulated by using the Monte Carlo method, and for every DEM realization, the topographic index and distance to the drainage outlet were extracted. Secondly, the obtained topographic index and the distance to the drainage outlet were input to the TOPMODEL to simulate seven rainstorm-flood events, and four evaluation indices, such as Nash and Sutcliffe efficiency criterion (EFF), sum of squared residuals over all time steps (SSE), sum of squared log residuals over all time steps (SLE) and sum of absolute errors over all time steps (SAE) were recorded. Thirdly, these four evaluation indices were analyzed in statistical manner (minimum, maximum, range, standard deviation and mean value), and effect of DEM uncertainty on TOPMODEL was quantitatively analyzed. Finally, the simulated hydrographs from TOPMODEL using the original DEM and realizations of DEM were qualitatively evaluated under each flood cases. Results show that the effect of DEM uncertainty on TOPMODEL is inconsiderable and could be ignored in the model's application. This can be explained by: 1) TOPMODEL is not sensitive to the distribution of topographic index and distance to the drainage outlet; 2) the distribution of topographic index and distance to the drainage outlet are slightly affected by DEM uncertainty.