Impact of DEM cell size on calibration and predictions of runoff and sediment, using SWAT-CU P

Hydrological conceptual models such as SWAT lay on numerous inputs and parameters that make calibration process complicated and time consuming. Digital Elevation Model (DEM) is one of the important inputs that its resolution affects watershed delineation and models simulations. However, DEM with more fine pixels is costly. This paper aims to assess the effect of DEM resolution on parameters calibration and estimation of runoff and sediment in the SWAT model. To this end, three sources of DEM with 50, 90 and 1000 meter pixel sizes are applied for daily rainfall-runoff and sediment simulation within the Gamasyab watershed. Furthermore the parameters, which are directly derived from DEM like watershed slope and river slope, are excluded from calibration process. The calibration of the model was done by SWAT-CUP that uses inverse modeling approach. It is observed that the runoff simulation results by the three DEMs are relatively similar. However, in case of sediment, the differences were a little more significant. The reason for these similarities can be attributed to the non-uniquness property of inverse modeling, in which an observe signal could be reproduced by many different parameter sets. Therefore, considering limitations about available observations for calibration process; significant improvement in results cannot be expected while using three DEM cell sizes.