How do geological map details influence geology-streamflow relationships in large-sample hydrology studies?

Abstract. Large-sample hydrology datasets have advanced hydrological research, yet the impact of landscape attribute level of detail on inferring dominant streamflow generation processes across scales remains underexplored. This study investigates the role of geology using maps of increasing detail—global, continental, and regional—each reclassified into four relative permeability classes. These geological attributes, combined with topography, soil, vegetation, land use and climate attributes, were analyzed across 4,000 European catchments from the EStreams dataset, to identify dominant controls on streamflow signatures. We conducted analyses at three scales: large (63 European river basins), intermediate (the Moselle basin), and small (five Moselle sub-catchments). The large-scale study used global and continental maps, while the intermediate and small-scale experiments also incorporated regional maps. On the large scale, no consistent correlation emerged between baseflow and landscape attributes, though landscape effects outweighed climate influences. The continental map generally showed stronger correlations than the global map, but with tradeoffs in the number of geological classes versus spatial resolution. At the intermediate scale, geology transitioned from being insignificant to dominant as map detail increased, underscoring the importance of refined geological data. The small-scale experiment mirrored large-scale findings, showing varying dominant controls across catchments. However, the regional map provided consistent, physically meaningful correlations, aligning with established hydrological understanding. Overall, this illustrates the considerable benefit of integrating detailed, region-specific geological data into large sample hydrology studies. Overall, our findings have implications for hydrological regionalization and the prediction of streamflow in ungauged catchments.