Warming slows the drainage of Alpine catchments

The mechanisms by which mountain landscapes store and release water are undergoing profound transformation under a warming climate. Over the past half century, the Alps have experienced accelerated glacier retreat, reduced snow cover duration, and widespread permafrost thaw, all of which are expected to reshape groundwater–surface water interactions. How these changes affect the timescales of catchment water storage and discharge to streams remains largely unknown.Here, we analyze long-term streamflow recession behavior across more than 200 catchments in the Alps to quantify multi-decadal changes in drainage timescales. Individual streamflow recessions were automatically identified and fitted between discharge peaks and subsequent recharge events. For each event, storage-discharge parameters were estimated, and a characteristic recession timescale was derived. Although recession timescales exhibit substantial spatial and temporal variabilities, we found that their aggregated behavior reveals a coherent long-term signal.Across the Alps, streamflow recession timescales increase markedly from the mid-1970s onward, with the multi-catchment mean rising by more than 20 days and remaining persistently elevated thereafter. This widespread lengthening indicates that Alpine catchments are draining more slowly today than in the mid-20th century. The timing of this shift closely coincides with the onset of accelerated warming and points to a climate-driven reorganization of subsurface storage and drainage. The strongest increases occur in high-elevation catchments of the northern and central Alps, where pronounced changes in precipitation regimes, permafrost thaw, increasing evapotranspiration demand, and reorganization of groundwater flow partitioning jointly promote slower drainage. In contrast, lower-elevation and southern Alpine catchments exhibit weaker changes, consistent with a more stable, rainfall-dominated hydroclimate. We conclude by presenting a conceptual framework for the coupled cryo-hydrogeological processes driving this change and by discussing its implications for water resources in the Alps.