Snowmelt–Baseflow Lags as Indicators of Elevation-Dependent Storage Buffering in Snow-Dominated Mountain Catchments

Snowmelt is a critical seasonal water source in mountain catchments, yet the dynamics of catchment water storage and release, as well as the redistribution of snowmelt signals into low-flow periods, remain poorly constrained, particularly across the snow–rain transition. In this study, we focus on one diagnostic question: how long does the snow signal persist before it emerging in baseflow, and how does that lag change with elevation and snow regime? We analyse 88 near-natural mountain catchments in Czechia and Switzerland using HBV-Light simulations of snow water equivalent (SWE) and baseflow and apply wavelet coherence to quantify phase-derived SWE–baseflow lags as a signal-based indicator of storage modulation. Across both regions, SWE and baseflow exhibit stable annual coupling, with SWE consistently leading baseflow. Mean lags are systematically longer in higher, colder, and snow-richer catchments, consistent with stronger storage buffering and delayed meltwater release. At the regional scale, the characteristic lag is ~69 days in Czech catchments and ~100 days in Swiss catchments, and the lag increases with elevation in both countries. These storage-linked delays align with stronger snow support to summer baseflow at higher elevations, while mid-elevation catchments near the snow–rain transition show shorter lags and weaker persistence of snow influence. This lag-based indicator provides a compact, transferable way to diagnose where snowmelt most strongly sustains baseflow through storage buffering, and where this mechanism is most likely to weaken as snow seasons shorten under warming.