Changing discharge patterns of springs characterized by nival flow regimes in the Austrian Alps

Alpine spring runoff patterns recorded at gauging stations offer a unique observational window into the hydrological state of Alpine water systems. These systems play a crucial role in supplying water to downstream areas and are particularly sensitive to changes in temperature and precipitation. Using a dataset of spring discharge monitored at 29 stations by the Austrian Hydrographic Service, spanning 24 years, we conducted a trend analysis on both the quantity and timing of mean and extreme flows. The springs, which were clustered into groups based on the Pardé coefficient and autocorrelation analysis, are distributed over the whole area of the Austrian Alps with mean catchment elevation reaching up to 2500 m above sea level. The trend analysis was performed using the Mann-Kendall test and the Theil-Sen slope on seasonally and annually computed statistics describing the quantity and timing of the occurrence of mean and extreme flows. The results indicate that at springs with a nival flow regime (i.e., flow dominated by snow melt), winter discharge increased. However, during the summer period, differences emerged between two characteristic spring groups: (i) springs at higher-elevation catchments, mainly distributed in the west of the Austrian Alps, with a positive trend in summer, and (ii) springs in the eastern part of the Northern Alps, that displayed a decrease in summer discharge. Notably, differences in the trends for timing of maximum and minimum flows were also evident between these two groups. Furthermore, we compared the hydrological trends to precipitation trends in the spring areas to assess relationships between meteorological and hydrological patterns. These findings provide valuable insights into how the spring runoff patterns have evolved in the Austrian Alps over the past 24 years.