Title Projection of future sea level changes around Taiwan
Dept Transportation Technology Research Center
Year 2016
Month 3
Price
Summary In recent years, global sea level rise resulting from global warming has been one of the highly respected and important issues. Since the rates of sea level changes are not uniform in worldwide oceans and sea level trend around Taiwan is rising and faster than global averaged trend, accurate estimation and projection of sea level changes around Taiwan are both extremely important.

Traditionally, tide gauges and satellite altimetry are the common instruments used to determine sea level changes; however, the time span of data (< 20 years) is too short to avoid the influence of low-frequency signals on determining sea level trend. In this study, we attempt to analyze the relationship between climate factors and sea level around Taiwan by two techniques, including Ensemble Empirical Mode Decomposition (EEMD) method and multivariate fitting method. We will also focus on understanding the contributions of sea level rise around Taiwan using the combination of satellite altimetry data, space gravimetry data and in-situ ocean temperature and salinity data. Finally, the future sea level change projection around Taiwan is calculated using the trends derived from satellite altimetry data.

The results show that the sea level trend from altimetry data, corrected by low-frequency signals from tide gauges decomposed by EEMD, is not significantly improved (the trends without and with low-frequency correction: 1~8 mm/yr and 1~7 mm/yr). On the other hand, we used multivariable linear function to fit altimeter measurements during the period of 1993-2012 which allows us to reduce impacts of interannual (El Niño Southern Oscillation, ENSO) and decadal (Pacific Decadal Oscillation, PDO) climate factors on the determination of sea level trend around Taiwan. Without considering the impacts of climate factors, the absolute sea level trends around Taiwan derived by six-parameter fitting method gradually increase from the north of Taiwan at a rate of 2~3 mm/yr to the south of Taiwan at 8~12 mm/yr; however, the rates of sea level trends are roughly uniform (-2~4 mm/yr) using the multivariate fitting method.

The ENSO phenomenon strongly influences the regional sea level within the latitude of 20°N~20°S, and sea level all around Taiwan could be possibly affected by PDO phenomenon. Moreover, the results of sea level budget show that steric sea level and ocean mass changes contribute to total absolute sea level at the northeast of Taiwan at a similar rate, but contribute about 70%~90% and 20% at the southeast of Taiwan, respectively. In the western ocean of Taiwan, the temperature and salinity data are lack, so the steric sea level is not accurate. Finally, the projected sea level around Taiwan by 2050 with and without considering climate factors would reach 200 m and 90 m relative to the estimated sea level in 2012, respectively.
Post date 2016/05/12
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