Preliminary Study on Responses of Offshore Tidal Level to Sea Temperature Rise in the Yangtze River Estuary

Warming of the climate system is unequivocal. The 5th IPCC report points out that the sea temperature shows a warming of 0.85 (0.65 to 1.06) °C, over the period 1980–2010. Over the period 1901 to 2010, the global mean sea level has risen by 0.19 m. Meanwhile, the rate of sea level rise due to sea temperature rise during 1963 to 2003 with the value 0.4-0.6 mm/y is smaller than that during 1993 to 2003 with the value 1.0-2.0 mm/y. However, the contribution of sea temperature rise on sea level rise is not clear. In this paper, the Yangtze River Estuary is chosen as a prototype to preliminary study the responses of the mean tidal level change to the sea temperature. Firstly, MIKE21 is selected to establish a depth-averaged sea temperature numerical model covering the Yangtze River Estuary and the Hangzhou Bay. Then, this model is well validated with the measured data. The temperature data from 1960 to 2008 at the Yinshuichuan and Chengshan stations are applied to analyze the sea temperature trend in the Yangtze River Estuary. The rates of STR at the two stations are both 0.025 °C/y, which is regarded as the sea temperature rate in the Yangtze River Estuary. The sea temperatures at boundaries are raised 0.25, 1 and 5 °C respectively to represent the sea temperature in 10, 40 and 200 years later. The results indicate that 1) the mean tidal level rises as the sea temperature increases; 2) the mean tidal level increase at the Dajishan station is greater than that at the Lvsi station; 3) the amplification rate of mean tidal level decreases as the sea temperature increases, which shows that the mean tidal level increases nonlinearly as the sea temperature increases.