Naslov
Will the future sea-level rise result in the North Adriatic flooding episodes of longer duration?

Autori
Orlić, Mirko ; Pasarić, Miroslava

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Lagoons and Coastal Wetlands in the Global Change Context: Impacts and Management Issues / - Venecija : Unesco, Corila, 2004, 33-34

Skup
Lagoons and Coastal Wetlands in the Global Change Context: Impacts and Management Issues

Mjesto i datum
Venecija, Italija, 26.04.2004. - 28.04.2004

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
flooding; atmospheric forcing; sea-level rise; Northern Adriatic

Sažetak
Tide-gauge data, collected at Venice and Bakar over 9 and 17 years, respectively, are analyzed in order to document sea-level variability in the North Adriatic. It is shown that residual sea levels are similar at the two stations, with some differences existing in the tidal regime (Pasaric and Orlic, 2001). A number of processes, contributing to the sea-level fluctuations, are isolated: (1) tides, (2) storm surges and seiches generated by synoptic-scale atmospheric disturbances, (3) response of the sea to the planetary atmospheric waves, (4) seasonal and year-to-year variability, (5) interdecadal variability, and (6) change of mean sea level (Orlic, 2001). It is found that among these processes the first four were most important for the occurrence of floods. The original time series are therefore decomposed into the four components: (i) the tides are calculated using seven harmonic constituents, (ii) seasonal signal is determined by fitting a sum of an annual and a semiannual sine to the series previously subjected to a low-pass filter (with the cut-off period being placed at 10 days), (iii) the "planetary" part is obtained by removing seasonal signal from the low-pass filtered values, and (iv) the "synoptic" part is determined by high-pass filtering the sea levels from which the tides have been removed. A flooding event is then defined as every case of hourly sea level exceeding the 99.5 percentile threshold value, and a flooding episode as an occurrence of at least two successive flooding events within 24 hours. From 17 years of Bakar data 761 events and 110 episodes are thus extracted, the longest episode lasting more than 200 hours. It is found that the longest episodes were predominantly caused by planetary atmospheric waves, whereas synoptic atmospheric disturbances gave rise to the shorter, albeit more intense episodes. In the future, the occurrence of extreme sea-level events and episodes could be significantly affected by changes in the mean sea level. Due to the expected warming, the global mean sea level is projected to rise 48 cm (with a range of uncertainty of 9-88 cm) by the year 2100 (Church et al., 2001). In order to get an insight into the possible consequences, we examine the effects of a moderate 30 cm mean sea-level rise on the existing statistics, by reducing the above mentioned threshold level by this amount. Underlying assumption is that the global rise of mean sea level will not be modified by regional processes, and that the other processes contributing to the sea-level variability will not be influenced by the climatic change. We find that the number of events would be greater more than 20 times, and that the number of episodes would increase to 554. The weeks lasting episodes would not be exceptional, and the longest one would last more than 62 days! The importance of planetary atmospheric waves would be further enhanced, since they provide the major contribution to long episodes. Of course, the statistics would be somewhat different with a different selection of the threshold value. But - to return to the question posed in the title of this contribution - the future rise of mean sea level is likely to support not only an increase in the frequency of floods but also a lengthening of the flooding episodes in the North Adriatic coastal zone. References Church J. A., Gregory J. M., Huybrechts P., Kuhn M., Lambeck K., Nhuan M. T., Qin D. and Woodworth P. L. (2001): Changes in sea level. J. T. Houghton et al. (Eds): Climate Change 2001 - The Scientific Basis, Cambridge University Press, Cambridge, 639-693. Orlic M. (2001): Anatomy of sea level variability - an example from the Adriatic. F. El-Hawary (Ed): The Ocean Engineering Handbook, CRC Press, Boca Raton (USA), 1.1-1.14. Pasaric M. and Orlic M (2001): Long-term meteorological preconditioning of the North Adriatic coastal floods. Continental Shelf Research 21, 263-278.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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