In this study, we found large uncertainties in the simulation of Subsurface Stormflow (SSF) in a lumped hydrological model using only discharge data for parameter estimation. High-flow-based parameter estimation could extract some additional information, but SSF-specific data remain necessary to achieve more realistic SSF simulations. Occurrence uncertainty dominated total SSF uncertainty, suggesting proxy data on SSF occurrence could already substantially reduce SSF simulation uncertainties.

Many streams do not always contain flowing water. Because these streams are rarely monitored, we tested whether observations by citizen scientists could be used to track whether streams were flowing. Although these observations were irregular in space and time, identifying the order in which sites started or stopped flowing allowed us to fill data gaps and estimate daily flow conditions across the area. This shows that volunteers can effectively monitor streams that sometimes dry up.

We studied how well simple bucket-type models can reproduce observed river flow using large data sets from many regions in the world. Model performance varies widely depending on local conditions, so fixed performance thresholds are misleading. To better judge model performances, we propose lower and upper benchmarks. These benchmarks help to better understand what level of model performance is achievable and, thus, enable us to compare models across different catchments.

We show that geological maps with varying levels of detail may influence the identification of geology–streamflow relationships across European catchments at multiple scales. At the large scale, controls varied between basins, with no map consistently superior. At the intermediate and small scales, however, higher geological detail consistently strengthened correlations, particularly for baseflow signatures, with the regional map highlighting controls more consistent with process understanding.

Rain falling on snow (RoS) can accelerate snowmelt and affect runoff, potentially causing severe flooding. We assessed the regional and seasonal variations in the occurrence of RoS in mountainous catchments in central Europe under different perturbations of future climate. Our results showed that RoS changes driven by climate change vary greatly among regions, across elevations, and within the cold season. However, most projections suggested a decrease in RoS events and RoS-driven runoff.