Transnational assessment of HydroBASINS catchment areas against official ICPDR and ISRBC data

DOI registering

Abstract

This study assessed the accuracy of HydroBASINS catchment-area estimates against official ICPDR and ISRBC values for 23 catchments in the Danube River Basin, many spanning international and EU–non-EU boundaries. HydroBASINS polygons at hierarchical levels 3 through 7 were dissolved and reprojected to the EPSG:3035. Agreement was assessed using a paired t-test, the Wilcoxon signed-rank test, linear regression, the Bland–Altman method, Spearman rank correlation, and the Area Accordance index. No statistically significant systematic difference was found between the datasets (paired t-test, p = 0,179; Wilcoxon signed-rank test, p > 0,05). Relative deviations were below 4 % for 19 of 23 catchments, while the mean Area Accordance was 0,9668, with higher values for larger catchments. The Vrbas (18,13 %) and Ialomita (13,54 %) catchments exhibited the largest deviations. Independent delineation using GRASS GIS/SRTM and MERIT Hydro produced highly consistent catchment-area estimates for the Vrbas catchment, supporting the interpretation that its discrepancy from the official value is more likely related to catchment definition in karstic terrain, whereas more divergent estimates were obtained for the Ialomita catchment, suggesting greater sensitivity to DEM selection in low-gradient terrain. HydroBASINS provides generally reliable catchment-area estimates for regional applications in the Danube Basin, but caution is needed in karstic and flat areas.