“…As experimental evidence has mounted on the mutual links among the hydrochemistry of waters in storage and in fluxes, climatic regimes, soil and landscape attributes, and the age of streamflows [e.g., Weiler and Fl€ uhler, 2004;McGuire et al, 2005;Hrachowitz et al, 2009;Soulsby et al, 2011;Tetzlaff et al, 2014], a growing awareness has developed of the fundamental importance of a unifying theoretical framework for catchment-scale flow and transport phenomena [e.g., Rinaldo and Marani, 1987;Kirchner, 2003;Sivapalan et al, 2003]. Such a framework must formally characterize the age dynamics in hydrologic systems and, as a consequence, comprehensively recapitulate hydrograph and tracer information.…”