Streamflow sensitivity regimes of alpine catchments and their relationship with elevation, temperature, and glacier cover

Alpine streams supply water to mountains and downstream regions, but their sensitivity to climatic variability is complex. Here we resolve seasonal and elevation-dependent patterns of streamflow sensitivity using long-term records from the European Alps. For each week of the year, we fit a multiple linear regression model that predicts streamflow as a function of temperature, precipitation, and storage (approximated by streamflow from the previous week). The resulting regression coefficients quantify the direction and magnitude of the influence of the three predictor variables and thus represent weekly sensitivities of streamflow in response to changes in temperature, precipitation, and storage. At high elevations with extensive glacier cover, weekly temperature and precipitation sensitivities peak in spring and summer when melt rates are high. At low elevations with no glacier cover, weekly temperature sensitivities are negative in summer, while precipitation sensitivities are highest under moist winter conditions. Storage sensitivities are particularly high at high elevations in winter, when streamflow is mostly sourced from subsurface storage. Our results indicate how the transition zone, which marks a change from negative to positive temperature sensitivities in spring and summer, could shift upwards with climate warming, showing that streamflow sensitivities are temperature-dependent and thus non-stationary. Weekly streamflow sensitivities enhance our understanding of the main drivers of the streamflow regime and can be used for the evaluation of hydrological simulation models.