We find that flow-weighting the tracer concentrations in streamwater resulted in roughly 26 % larger young water fractions compared to the corresponding unweighted values, reflecting the fact that young water fractions tend to be larger when catchments are wet and discharge is correspondingly higher. However, flow-weighted and unweighted young water fractions are strongly correlated with each other among the catchments. They also correlate with terrain, soil and land use parameters, as well as with mean precipitation and measures of hydrologic response.
Within individual catchments, young water fractions increase with discharge, indicating an increase in the proportional contribution of faster flowpaths at higher flows. We present a new method to estimate the linear slope of this relationship between flow and young water fractions, which we call the discharge sensitivity of Fyw. Among the 22 catchments, discharge sensitivities of Fyw are highly variable and only weakly correlated with Fyw itself, implying that these two measures reflect catchment behaviour differently.