Storm climate and morphological imprints on the danube delta coast

Abstract

Coastal storms hitting the Danube Delta coast are recurring high-energy events (of high winds and waves), which in most cases are the result of Mediterranean (extratropical) cyclones following different trans-Balkan routes. By using long-term wind (1962–2012) and wave (1949–2013) data, we investigated the climatology of storms and their impact on the deltaic coast. There are on average 30 storms/year occurring with a distinct seasonality, from which ca. 3 events/year correspond to severe storms (wind speed v ≥ 20 m/s; significant wave height H s ≥ 4 m) usually registered during the winter months. Storminess shows a significant multidecadal variability with certain periods of increased activity as during the late ’60s, the ’70s and the ’90s, and less active in the ’80s or 2000s especially since 2006. These periods correlate well with the variations in the teleconnection patterns over Europe (NAO, EA, EARW, SCAND with −0.76, −0.55, 0.56, 0.55 as correlation coefficients). A 5-category scale of storms has been established using wind speed thresholds and associated wave heights that define morphological changes on the coast. The extreme storm of January 1998 is the only category V event for which data on topographic change is recorded, suggesting significant sediment losses and an extremely variable longshore response dictated by shoreline exposure to storm waves and pre-storm site morphology. Moreover, the large prevalence of the northern waves during storms created an apparent unidirectional (southward) development of the coastal features—islands, spits, and beach barriers, subaqueous deltaic platforms, depocenters—and finally ended up by conferring an asymmetric architecture to each of the five open-coast lobes with completely distinct features updrift (sandy strandplains) and downdrift (barrier-marsh plains and deltaic mud plains) of the river mouth.