Evaluation of Open Source Dems for Regional Hydrology Analysis in a Medium-Large Basin

Nowadays exist a variety of topographic source with different spatial resolution obtained by using distinct methodologies. Choosing a data source that is the more accurately possible in area relief, has become fundamental in hydrological studies. The aim of this study is to compare the accuracy of four open source DEMs (TOPO_IGN, SRTM_30m, SRTM_90m and ASTER-GDEM) in the Quequen Grande River Catchment (QGRC), in the south-west of Buenos Aires Province in Argentina, in two different ways. Determining the vertical error of four source DEMs using geodesic points established by the National Geographic Institute of Argentina (GCP_IGN); and examining the association of DEMs error with hydrological parameters associated to drainage network obtained in each case. The results confirmed differences between GCP_IGN and open source DEMs elevation values. The Root-Mean-Square Error (RMSE) value shows that the uncertainty of elevation measurement is bigger in high altitudinal zones. This is due to two factors (i) the complex landscape pattern in areas characterized by high elevation values within flat study area; and (ii) the level of precision and spatial resolution of each open source DEM. The calculated slope is overestimated in all DEMs, indicating a positive bias and due to this, that slope accuracy is influenced by terrain roughness and pixel size of DEM, mainly. The extract catchments and drainage information from all DEMs area also affect the outcome. The terrain morphology strongly influences the DEM accuracy. So, coming to a conclusion, as in a QGRC, that include zones with high slopes and flat areas, SRTM_30m can be used to obtain height data. SRTM_90m can be used to obtain automatic drainage and catchment delineation. Both DEMs are similar to the obtained by using IGN topographic data. Lastly, the ASTERGDEM model although possessing a high spatial resolution, turned out giving the lesser appropriate topographic information. These results can be useful for further hydrological, agronomical and environmental studies that employ these DEMs in modeling exercises.