Hydroclimatic change reorganizes karst spring discharge in the Alpine region across discharge regimes and karst-system properties

Felix Joger , Zhao Chen, Andreas Hartmann, Stefan Broda

Karst springs are important water resources for the Alpine region and are particularly sensitive to hydroclimatic change due to their comparably short response times. Yet how their hydroclimatic responses differ among discharge regimes and karst systems with different storage properties remains poorly understood. We analyzed 85 karst springs across the wider Alpine region over 2003-2022 to assess how recent trends in discharge, precipitation, and temperature vary across (i) contrasting discharge regimes and (ii) karst-system response types. To this end, we performed clustering based on discharge seasonality and derived three response types using an established karst-system classification framework. Trends in annual, seasonal, and monthly hydrometeorological variables, as well as in the magnitude and timing of low and high flows, were assessed using the modified Mann–Kendall test and Sen’s slope estimator. Results showed that seasonal flow redistribution was more pronounced than annual discharge change, with widespread increases in winter discharge. Responses differed strongly among the four identified discharge regimes. Winter-pluvial springs in the peri-Alpine region tended toward decreasing spring and summer discharge and increasing winter discharge, resulting in increasing seasonality, with these changes largely associated with precipitation trends. Low and high flows showed corresponding changes, with decreasing low-flow and increasing high-flow magnitudes. In contrast, snow-influenced springs in the core Alpine region showed decreasing seasonality, characterized by mostly increasing winter discharge and decreasing summer discharge, consistent with reduced snow storage and earlier snowmelt. Low-flow magnitudes generally increased, and low-flow occurrence shifted earlier. Thus, these contrasting seasonal shifts suggest that winter water-availability constraints may be reduced in the core Alpine region, whereas reduced summer discharge may increasingly constrain water availability in the peri-Alpine region. Discharge trend patterns were more clearly structured by discharge regime than by karst-system properties. However, trend magnitudes and variability among springs generally decreased from faster- to slower-responding systems. Overall, karst springs in the wider Alpine region respond clearly but heterogeneously to hydroclimatic change, highlighting their value as regional climate indicators and the need for sustained long-term monitoring.