Trend analysis of Alpine spring discharge: Interplay between climate and discharge characteristics

Springs provide an important water source in alpine regions, particularly during dry periods. Many originate from high catchments, making them valuable indicators of climate change impacts on mountain hydrology. Despite their importance, relatively little is known about past climate change effects on spring discharge. This study analyzed discharge and meteorological data from 27 Austrian springs (1997-2022) to assess trends across distinct spring groups. The springs were classified - based on an existing typology - into four groups: fast-responding karst springs in the Northern Calcareous Alps, high-alpine snow-dominated springs, fractured rock springs in the southern Alps influenced by Mediterranean climate, and lowland springs with damped responses in the eastern foreland. The Mann-Kendall test and Sen's slope estimator were used to assess trends in annual discharge, seasonality, and magnitude and timing of extreme flows. Results showed a widespread increase in winter discharge and a general rise in low flows across most springs. Other hydrological responses varied by spring group: karst springs in the Northern Calcareous Alps showed reduced seasonality, earlier onset of high and low flows, and declining spring and summer flows, while high-alpine springs generally exhibited stable discharge. The most notable changes were observed in the low-flow regime of fast-responding karst springs, highlighting their sensitivity to shifts in snow dynamics driven by rising temperatures. Across spring types, the clearest hydrological signals were seasonal shifts, rather than changes in annual discharge volumes. Trends in some high-elevation spring flows did not consistently align with local hydrometeorological trends, suggesting that gridded climate datasets may not fully capture changes in high-altitude catchments with complex recharge areas. These findings highlight the growing need for better monitoring and modeling to improve predictions of future water availability in mountain catchments.