Assessing grid size effects on runoff and flow response using a GIS-based hydrologic model

The effects of grid size on model parameters and on the performance of a GIS-based hydrological model intended for flood simulation is assesses in this paper. The WetSpa model is used to estimate runoff and flow discharge in the 1176 km2 Alzette river basin, Grand-duchy of Luxembourg. The GIS ArcView and its spatial analyst are used to extract hydrological model parameters from DEMs, soil and land use maps with cell sizes of 50, 100, 200, 400 and 800m. The value of the model parameter derived from the 50m data is used as the reference value, with estimates of model parameters of coarser resolutions compared against it. Results show that in this integrated model the grid size has a considerable effect on runoff and outflow hydrographs. However, coarser grid cell resolutions can be used for runoff simulations as long as parameters are appropriately calibrated.