Analysis of the eastern Adriatic sea level extremes

Abstract

Aim: To examine the frequency, strength, and driving mech-anisms of the eastern Adriatic sea level extremes. Methods: In 2017, a tide-gauge station, and a meteorological station have been installed at Stari Grad (Hvar Island, east-ern middle Adriatic Sea). Three years of sea level and at-mospheric measurements were analysed. Ten strongest ep-isodes of the following extreme types were extracted from sea level data: positive long-period (T >210 min) extremes; negative long-period (T >210 min) extremes; short-period (T < 210) extremes. Long-period extremes were defined as situations when sea level surpasses (is lower than) 99.7 (i.e., 2) percentile of residual long-period sea level height, and short-period extremes as situations when 2.5-h variance of short-period sea level oscillations is higher than 99.4 per-centile of total variance of short-period series. Types of sea level extremes were subsequently associated to characteris-tic atmospheric situations. Results: Positive long-period extremes commonly appeared during the presence of low-pressure atmospheric systems over the Adriatic – such system were accompanied with strong SE winds. Negative long-period extremes were as-sociated with presence of high atmospheric pressure fields over the Adriatic Sea, either with strong NE winds, or calm weather. Appearance of short-period sea level extremes corresponded to either low atmospheric pressure fields and strong SE wind, or normal/high pressure fields and calm weather/no winds over the Adriatic. A strong seasonal sig-nal was detected, with the positive long-period extremes occurring mostly during November to February, and the negative long-period extremes occurring during January to February. The short-period extremes appeared throughout the year, but strongest events appeared during May to July. Conclusion: Results show that Stari Grad is a flood-prone lo-cation, both when it comes to positive long-period extremes and to short-period extremes. Furthermore, long-period and short-period extremes occasionally occur simultane-ously in Stari Grad, pointing to a previously unknown added hazard level