Temporal Differentiation East China Sea-level Change, The Impact And Risk Assessment Mechanism

Research on sea-level change focuses on the studies of the trend, spatialvariation, mechanism of impact and risk assessment of sea-level change, etc. Thepaper defines the East China Sea as a major research area to study the spatial andtemporal variation of sea level in the East China Sea, and discusses the impact ofsea-level change caused by spindle variability Kuroshio on the East China Sea. Then,taking Shanghai as an example, it analyzes the inundation risk of the coastal cityinfluenced by extreme sea-level change on the East China Sea.Based on the sea surface height data from satellite altimeter, tide gauge stations,the paper discusses the sea-level change multiscale cycle, the spatial distribution,and the peak variation in China Sea. It also predicts the future trends and future peakyears of the sea-level change. It is suggested that sea level change on the East ChinaSea has noticeablly seasonal and interannual trends. What’s more, it also has theperiod of30months,134months,230months, in which the30-month period maybe related to quasi two-year cycle atmospheric oscillation (QBO); the134-monthperiod is consistent with the period of sunspot; the230-month period iscorresponding to the declination angle change of the moon cycle (18.6years).After the spatial analysis of the sea level in the East China Sea, the sea level nearthe Yangtze River in the East China Sea waters has remained high for long, whosegrowth rate is5.45mm/a, reaching the maximum in summer and declining year afteryear. Coupled with the impact of superimpose storm surges and astronomical tide, itmay pose a threat to the safety of life and property and the ecological environmentin Yangtze River Delta and its adjacent areas.Based on the monthly and average sea level data of China Sea peak, the studyindicates that the rate of change in the monthly peak level is higher than the averagein the East China Sea. The sea level peak increases every year, which is mainlyembodied by the violent oscillations of sea level. Yet the main reason of theoscillation is thermal expansion of seawater caused by global warming.Based on Winters exponential smoothing model for trend forecasting available, future sea-level change will maintain a rising trend, and it is expected that comparedwith2006, by2015, the sea level will rise by about40to50mm, and by2030, thesea level will rise by140to150mm. From the angel of the medium and large scale,considering the sea-level change influenced by PDO, ENSO, sunspots and otherfactors, and the primary cycle and the impact of the above superimposed cycles, thesea-level change in the East China Sea can be predicted to have the next peak inaround2025.The East China Sea Kuroshio is an important influencing contributor to sea levelchange in the East China Sea. The paper is based on temperature, salinity, velocitydata, etc., boundary delimitation Kuroshio, extract Kuroshio axis, and research onsea-level change in response to variability Kuroshio axis. The study has suggestedthat with different seasons, the Kuroshio axis wobble has obvious and differentcharacteristics of the southern, the northern and central spindle. In summer andautumn, as the flow velocity increases, the middle part of the East China SeaKuroshio axis deviation contributes to and affects the depth of100m. As the spindlevelocity increases, the Kuroshio entrance to both the left and right side of theupward tends to rise in sea level, while sea level at the left side of the Kuroshiocentral spindle is on a declining trend, and the right side of the sea level is on the rise.As the Kuroshio with high speed flows to the north, it continuously exchanges energyand mass with the shelf water in the East China Sea, thus causing a declining speed inthe middle of the Kuroshio. With the declining speed in the main axis, the sea levelsat both sides tend to decline slowly or remain unchanged.Based on the ground-subsidence data, tide gauge data and tidal storm surgedata, with the paper accumulates the predicted rise of the sea level value, the groundsubsidence predictive value, the maximum surge storm values and the astronomicalhigh tide in2025(peak year) as the value of the extreme sea level in the East Chinasea. According to the previous sea-level predictions on the sea level trends, the papersets two scenarios which are the general and the strong typhoons in order to doinundated risk assessment in the Shanghai region. The results show that if a generaltyphoon hits Shanghai and the extreme sea level doesn’t reach the seawall’s height in Shanghai, it will not cause greater inundation risk to Shanghai if it doesn’t dike. If astrong typhoon sweeps Shanghai and overflowing embankment emerges, almost100%of the area will be flooded.