The Mechanism Of Sea Level Changes In Pearl River Estuary And The Accessement Of Coastal Flooding Risk

The Pearl River Delta is one of the most densely populated areas and one of the main economic hubs in China.The sea level of the Pearl River Estuary(PRE)is strongly affected by rapid economic development and also affected by the inflow of the Pearl River and water exchanges with adjacent ocean currents.The study of sea level change in this area can not only reveal the effect of human activities,but also reflect the comprehensive impacts of multiple factors,which will guide the reasonable utilization of marine resources and prevent the coastal flood inundation disasters of sea level rise.The nearshore and offshore sea levels show similar changes in the Pearl River Estuary.The long term sea level rise rate is 3.03±0.35 mm/a over 1954-2012.Since 1990 s,sea level has risen rapidly at the rate of 4.45±1.11 mm/a The long term sea level presents the change periods of 0.51,1,2~7,~19,~28 and ~43 years.The coastal ocean environmental changes are higher than the global mean level.The 0.06?/a rise rate of nearshore ocean temperature is faster than the offshore one,0.04? /a.Seawater acidification rate in the coastal water is 0.01±0.002 /a,which is faster than the global mean rate.The effect of humam activities on sea level in the PRE was studied using the path analysis method.Results show that land reclaim and land water inflow have direct impacts on sea level rise.The direct path coefficients of land reclaim and land water inflow on sea level rise are 0.17 and 0.16,respectively.Antropogenic activities have indirect impacts on sea level through the indicators of ocean temperature and seawater pH which reflects the carbon emission level.The total effects of population and per capita GDP on sea level are 0.38 and 0.34.The corresponding increase in population of 10 million will cause sea level rise about 0.05 m.Ten thousand dollors increase in per capita GDP will cause sea level rise about 0.04 m.The anomalously low/high sea level in PRE is related to El Ni?o/La Ni?a(EN/LN).The impact of EN/LN on sea level ranges from-8.70 ~ 8.11 cm and the periodic impact of EN/LN on local sea level is pronounced at ~3-year and ~5-year.Sea level in PRE responds to EN/LN in tropical Pacific Ocean with ~3 months lag.The main mechanism is that low/high SLAs in EN/LN events can be attributed to less/more seawater transported into the PRE through the anomalously weak/strong southward wind.The anomalously low/high sea levels are created through seawater convergent/divergent.At the same time,the local anomalously high/low sea level pressure also aggregates the low/high sea level anomalies.Sea level in the PRE will rise about 0.02 m in the next 5 years using the exponent smoothing method and rise about 0.15~0.26 m in the next 10 years based on the social economic effects.The nonlinear prediction using neural network method shows that sea level rise rate will increase from the present 3.03±0.35 mm/a to 3.58±0.28 mm/a in the next 15 years.The sea level in the north central South China Sea will rise about 0.18 m over 2041-2050 compared with that of 2012 using the numerical modeling method.The extreme water levels at recurrence periods(RP)of 500-year and 1000-year were simulated using the Monte Carlo method based on sea level rise,storm surge and the maximum astronomical tide.Under the extreme water level with RP of 500-year,the disaster affected population and economic loss will be at least 1 million people and 50 billion Yuan,respectively.At present situation,the RP of flooding level for Ling'ao nuclear power plant is only 362-year,which can't meet the design flood level with RP of 1000-year.