engleski

Long-term meteorological preconditions for the flooding of the North Adriatic coast

15. Events of flooding (acqua alta) of the North Adriatic coast are examined through 13-year series of hourly sea-level data, recorded at Bakar. The threshold-exceeding sea levels are studied in respect to three major contributions: (i) tides, (ii) elevations generated by synoptic and smaller-scale meteorological disturbances (storm surges and seiches of the Adriatic), and (iii) low-frequency oscillations (0.1 < f < 0.01 cpd) predominantly induced by planetary atmospheric waves, seasonal processes rendering only a minor contribution to the total sea-level maxima. Effects of meteorological forcing associated with the travelling cyclones, being the major contribution to the peak events, have amply been studied, and relative phases of the storm surge, the pre-existing fundamental Adriatic seiche and the astronomical tide have been recognized as the decisive factor for the flooding. However, the lower-frequency, planetary atmospheric waves can give rise to sea-level changes in the range of 70 cm, thus posing strong, days lasting preconditions for the flooding events. It is shown that in the absence of these long-period sea-level variations, the total number of sea-level events exceeding the 99.5% threshold value is reduced more than ten times. Consideration of the forecast of planetary-wave lows, which are best visible at the 500 mbar surface, may significantly improve the prediction of severe flooding events

North Adriatic; flooding; low-frequency variability; planetary-scale atmospheric disturbances

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