Current Trends of the Regime of Precipitation and Atmospheric Circulation over the River Basins in European Russia

The current trends of changes in precipitation and large-scale atmospheric circulation, significant for the seasonal structure and long-term changes in runoff in river basins in the mid and in the north of European Russia, are discussed. Taking into account seasonal variations and the phase regime, the analysis of spatial and frequency-temporal features of precipitation changes is carried out, their connection with large-scale circulation, as well as manifestations in the changes in annual and average monthly discharge in the river basins Severnaya Dvina, Mezen, Oka, and Belaya rivers. Changes in the amount of liquid precipitation during the snow cover onset/offset seasons are correlated with the air temperature in these seasons, and despite the lack of statistical significance of trends, are sufficient for the redistribution of the phase composition of precipitation and, as a consequence, for the formation of anomalies of winter runoff and the growth of spring runoff at the period of the beginning of flood as well. The connection of the liquid precipitation anomalies during the transition seasons the ongoing warming allow as to consider them as a trend, in a contrast to the anomalies of maximum spring discharge and of spring flood volumes in the north of European Russia, which are mainly caused by variations of large-scale circulation and rather to have a fluctuation feature. The obtained regressional and spectral estimates of the contribution of the Scandinavian mode to the annual runoff variability in the Severnaya Dvina basin show that the leading factor of its anomalies is the strengthening/weakening of the westerly transport described by this circulation mode in the opposite phase.