Climate-driven changes to streamflow patterns in a groundwater-dominated catchment

This study aims to investigate trends and regime changes in streamflow and basic factors driving these changes. The investigated area is located in central Poland and is influenced by temperate transitional climate. New insight is provided into the phenomenon of past climatedriven changes to streamflow patterns over a 65-year period (1951–2015). The Mann–Kendall test for monotonic trends and the CUSUM test are used to determine the presence or absence of changes in climatic variables, shallow groundwater level, and streamflow. Time series are explored to detect the direction of trends and the period when the significant change occurred. Differences in climatic conditions and streamflow patterns are discussed for two sub-periods, before and after the change. Overall, the results suggest stability in precipitation, with limited evidence for change in the annual amount, but reveal a significant change in streamflow regime in the 1980s, attributed to higher temperature driving evapotranspiration and reducing shallow groundwater recharge. It is concluded that the catchment is prone to increased evapotranspiration and in effect to greatly reduced runoff.