Interannual summer streamflow variability over Romania and its connection to large-scale atmospheric circulation

In this study, the spatial and temporal variability of summer (June–July–August, JJA) streamflow over Romania, as recorded at 46 hydrological stations over the period 1935–2010 is analysed. An empirical orthogonal function analysis and a canonical correlation analysis (CCA) were used to characterize the spatial and temporal variability of summer streamflow and its relationship with large-scale atmospheric factors. The dominant summer mode captures in-phase variability of river flow anomalies over the entire country, while the second mode of variability is characterized by a northwest–southeast dipole, emphasizing the influence of topography over the streamflow variability. Based on a CCA analysis, more than 50% of the summer streamflow variability is shown to be influenced by cloud cover and summer temperatures, via the modulation of precipitation and potential evapotranspiration. In general, positive (negative) streamflow anomalies, at country level, are associated with cyclonic (anticyclonic) circulation, the advection of moist (warm and dry) air, enhanced (reduced) precipitation and positive (negative) cloud cover anomalies