Spatial and temporal variability of winter streamflow over Romania and its relationship to large-scale atmospheric circulation

In this study we have examined the spatial and temporal variability of winter (DJF) streamflow over Romania as recorded at 46 hydrological stations over the period 1935 -2010. An empirical orthogonal function analysis (EOFs) was employed to characterize the spatial variability of winter streamflow. The dominant mode captures in-phase variability of river flow anomalies over the entire country. The second mode is characterized by a north-south dipole, emphasizing the influence of topography over the streamflow variability. Both modes are related with large-scale atmospheric circulation and sea surface temperature patterns. We show that the Arctic/North Atlantic Oscillation, East Atlantic, East Atlantic/Western Russia and Scandinavian patterns control a significant part of the interannual winter streamflow variability as captured by these two modes. Moreover, we show that the winter streamflow is very sensitive to the influence of winter temperatures. Positive streamflow anomalies are recorded during warm winters, which are favorable to precipitation fallen as rain, while cold winters can favor snowy winters and frozen ground and hence reduced winter discharges