Storm climate on the Danube delta coast: evidence of recent storminess change and links with large-scale teleconnection patterns

This paper presents an overview of storminess along the Danube delta coast since 1949 by analysing wind and wave data and discusses the influences of teleconnections on climate variability. To this end, a five-category storm classification is proposed based on wind speed intensity and storm duration. On average, this coast experiences 30 storms/year occurring predominantly in winter, three of them considered severe (categories III–IV). The extreme storms (cat. V) endanger most the coastal settlements and the back-beach ecosystems (sand dunes, wetlands, lagoons) and have a mean recurrence rate of 7 years, but occur with a large inter-annual variability more frequent during the late 1960s, the 1970s and the 1990s. The prevalence of northern storms, in particular for the severe ones (>90% frequency for wind speeds >20 m/s) is responsible for the vigorous southward longshore sediment transport, which shaped the Danube delta physiognomy over the last millennia. The application of the newly developed energetic (Storm Severity Index—SSI) and morphologic (Storm Impact Potential—SIP) proxies allowed the better assessment of both the storm strength and the temporal variation in storm energy. It appears that storm climate follows a cyclic pattern with successive periods of 7–9 years of high, moderate and low storminess in accordance with the main teleconnections patterns (North Atlantic Oscillation—NAO, East Atlantic oscillation—EA, East Atlantic/Western Russia—EAWR, Scandinavian oscillation—SCAND). If NAO succeeded to explain best most of the storminess evolution (r = −0.76 for 1962–2005), it failed during the latest decade (since 2006) when an unprecedented low in storminess occurred. There is also evidence of increased southern circulation during the latter period, associated with a reversal of correlation with NAO (from negative to positive). Significant correlations were also found for the EA, EAWR and SCAND (r = −0.55, 0.56, 0.55, respectively, significant at p