The North Atlantic Oscillation Influence on the Climate and Flow Variability of the Lower Danube Valley, between the Towns of Olteniţa and Călărăşi, Romania
Abstract: As previous international research has identified, the large-scale NAO atmospheric circulation pattern dominates climate variability in the northern hemisphere. In this study we investigate the impact of the North Atlantic Oscillation (NAO) index on annual/winter precipitation and river flow regimes for a sector of the lower Danube Valley. An important goal was to test the relation between the NAO pattern and the occurrences of extreme events. We assume that precipitation variability and river flow are harder to assimilate into a modified anthropogenic environment as the situation of the Danube in the study area. During the communist regime, this valley sector was transformed from a wetland environment into a farming area. Understanding NAO – rainfall and NAO – river flow relationships were based on monthly data in the time period between January 1977 and December 2010 for the NAO index, the river basin average precipitation over the Danube and the Danube river flow measured at Oltenita and at Calarasi Stations. Results showed that the large inter-annual variability in the precipitation regime and flows of the Danube is largely modulated by the NAO phenomenon. The four-time series in study are weak stationary, which means that the natural events vary moderately along a constant mean and the extreme events do not have the power to propagate, vanishing after few time steps.