Streamflow variability in the Tatra Mountains, Western Carpathians: Combined effects of climate change, teleconnection patterns, extreme events, and human pressure

Mountains are vital freshwater sources for nearly half of the global population but face increasing threats from climate change and human pressure. Understanding the impacts of these changes in mountain catchments is essential for developing effective mitigation strategies and conserving their unique ecosystems. Our study investigates the effect of climatic changes and large-scale teleconnection patterns (Arctic Oscillation, North Atlantic Oscillation) on streamflow dynamics in headwater mountain catchments under varying degrees of human pressure. The study is based on time series analysis of streamflow records, meteorological data, and teleconnection indices from 1971 to 2020, and employs trend analysis, wavelet analysis, and paired catchment observations.

Our findings reveal a significant increase in air temperature in the region (+0.4°C decade^-1) over the past 5 decades. While total precipitation remained stable, annual snowfall totals declined by 69 mm decade^-1. Air temperature and precipitation changes varied with altitude and season: temperature changes were more pronounced in summer at lower altitudes, while precipitation shifts were most evident in winter at higher altitudes.

Snow depths remained relatively unchanged, but snow cover duration decreased by up to 4 days per decade. These climatic shifts resulted in a notable increase in annual low flows (up to 11.5% per decade), as well as winter low, average, and high flows. The impact of teleconnection patterns on streamflow varied over time and was more pronounced at longer time scales (≥1 year).

Streamflow changes were more pronounced in semi-natural catchments compared to human-altered catchments. Climatic-driven streamflow trends were most evident in winter, while land use changes (windthrow) and human activities drove year-round trends. Precipitation and discharge exhibited stronger coherence across all time scales in human-altered catchments, suggesting greater susceptibility of these catchments to precipitation extremes. The amplification of the annual precipitation cycle and semi-annual snow cover cycle at higher altitudes, coupled with the intensification of the semi-annual streamflow cycle, underscores the impact of ongoing climatic changes. The observed streamflow variability reflects the intricate interplay of climate change, large-scale atmospheric oscillations, extreme events, and human activities.