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Báo cáo "Extreme values and rising tendencies of sea levels along Vietnam coast "

A review of the investigations on the sea 1eve1 changes in South-china sea is presented. The full set of year1y sea 1eve1 data at 25 tide gauges a1ong Vietnam coast is used for extreme analysis and trend analysis. Based on the level data collection up to year 2007 the empirical extreme analysis yields new estimates of the design values of sea level with different rare frequencies. The results of extreme analysis are compared with the theoretical extreme heights of tide obtained by predicting hourly tide heights in a 20-year period. . | VNU Journal of Science Earth Sciences 25 2009 116-124 Extreme values and rising tendencies of sea levels along Vietnam coast Hoang Trung Thanh Pham Van Huan College of Science VNU Received 5 August 2009 received in revised form 23 August 2009 Abstract. A review of the investigations on the sea level changes in South-china sea is presented. The full set of yearly sea level data at 25 tide gauges along Vietnam coast is used for extreme analysis and trend analysis. Based on the level data collection up to year 2007 the empirical extreme analysis yields new estimates of the design values of sea level with different rare frequencies. The results of extreme analysis are compared with the theoretical extreme heights of tide obtained by predicting hourly tide heights in a 20-year period. For stations with 11 harmonic constants of main tidal constituents the theoretical astronomical extreme tide levels were calculated by the Peresipkin iteration method. The comparison showed a good agreement between two methods. The analysis also showed that the tidal extremes and design level values of 20-year return period are of the same range. The level values of longer return period are affected mainly by floods and surges at a decreasingly extent. The rate of yearly changes of sea level due to global warming and other effects is evaluated to be about 1 mm per year. Keywords Extreme analysis Trend analysis Return period Design levels Sea level rise. 1. Introduction The extreme sea levels are research subject of many purposes. The maximal and minimal values of sea levels and their occurrence probabilities are taken into account in designing hydro-technical installations and in building navigation maps with minimum sea level being the zero of the navigation maps. The issues of sea level changeableness are of a common interest especially in the context of the global warming. The observation of sea level along Vietnam coast is mainly carried out by a system of tidal Tel 84-912116661 E-mail