Change of Annual Extreme Water Levels and Correlation with River Discharges in the Middle-lower Yangtze River: Characteristics and Possible Affecting Factors

As one of the fastest developing regions in China, the middle-lower Yangtze River （MLYR） is vulnerable to floods and droughts. With obtained time series of annual highest water level （HWL）, annual lowest water level （LWL） and the corresponding fiver discharges from three gauging stations in MLYR that covering the period 1987-2011, the current study evaluated the change character- istics of annual extreme water levels and the correlation with fiver discharges by using the methods of Vend test, Mann-Whitney-Pettitt （MWP） test and double mass analysis. Major result indicated a decreasing/increasing trend for annual HWL/LWL of all stations in MLYR during the study period. A change point in 1999 was identified for annual HWL at the Hankou and Datong stations. The year 2006 was found to be the critical year that the relationship between annual extreme water levels and fiver discharges changed in the MLYR. With contrast to annual LWL in MLYR, further investigation revealed that the change characteristics of annual HWL were highly consistent with regional precipitation in the Yangtze River Basin, while the linkage with Three Gorges Dam （TGD） operation is not strong. Our observation also pointed out that the effect of serious down cutting of the riverbed and the enlargement of the cross-section area during the initial period of TGD operation caused the downward trend of the relationship between annual LWL and river discharge. Whereas, the relatively raised river water level before the flood season due to TGD regulation since 2006 explained for the changing upward trend of the relationship between annual HWL and river discharge.

Characteristics Analysis and Risk Assessment of Extreme Water Levels Based on 60-Year Observation Data in Xiamen, China

Extreme water levels are related to astronomical tides and storm surges.Eleven typhoon systems,which have caused extreme water level rises,were selected based on 60-yr water level data from the Xiamen tide gauge station.In these 11 typhoon systems,the astronomical tide component accounts for 71%-95%of the total water level.The Gumbel distribution of extreme water level rise was estimated,and the impact of typhoon surges on water levels during the return period was analyzed.The ex-treme tide levels caused by typhoons Herb(1996)and Dujuan(2015)are much higher than those of other typhoons and correspond to the return period of 76 yr and 71 yr,respectively.The differences of sea levels in the presence and absence of these two typhoons in the 10-100 yr return period are 5.8-11.1 cm.For the 100-yr return period,the total risks within 10,25,50,and 100 yr increase by 94.3%,85.4%,72.9%,and 54.4%,respectively,if the Herb and Dujuan are not considered.Assuming that typhoon Herb(1996)occurred during the highest astronomical tide,it will produce a water level higher than that of the 1000-yr return period.Sea level rise has an important influence on the water level return period,and the contribution of nonlinear sea level rise in the next 100 yr is estimated to be 10.34%.

Changes in key indicators of coastal marine climate in China

Based on the observation data from China coastal marine stations,the key indicators of marine climate along China coast were explored,including sea surface t emperature(SST),sea level and sea ice.Results show that:(a)The SST along China coast continues rising and increased by 0.25℃/decade during 1980-2019,the warming accelerated significantly after 2011 and it has been well above normal for five consecutive years since 2015.In 2019,the average SST along China coast was 1.1℃ higher than normal(with 1981-2010 taken as a reference period),ranking the highest since 1980.Besides,the SST extremes have been explored based on four long-term marine stations for the period 1960-2019.(b)Sea level along China coast continues to rise at an accelerated rate.The mean sea level rise rate along China Coast was about 2.4 mm/yr during 1960-2019,3.4 mm/yr during 1980-2019,and 3.9 mm/yr during 1993-2019,with significant regional differences.The relatively stronger sea level rise trends were observed along the coastal waters of the Bohai Bay,the Laizhou Bay,the Yangtze River Estuary,the Pearl River Estuary,and the Hainan Island,respectively.Besides,the extreme sea levels along China coast showed an obvious upward trend from 1980 to 2019.During this period,the annual rise rate of extreme high water level along China coast was 4.4 mm/yr,and had obvious regional characteristics,with the highest rate of 9.9 mm/yr observed at Yantai of Shandong Province,(c)The annual sea ice period and sea ice cover of the Bohai Sea(BS)decreased substantially during 1963-2019 by 0.7-1.3 days/yr and 45-59%/yr,respectively,and the decrease rate of ice cover is larger in the north than that in the south.2019 was the year of light icing.

Prediction of China's Submerged Coastal Areas by Sea Level Rise due to Climate Change

Based on the simulation with the Ocean-Atmosphere Coupled Model CCSM and Ocean Model POP under the green- house gas emission scenario of the IPCC SRES A2 （IPCC, 2001）, and on the earth crust subsidence and glacier melting data, the relative sea level change is obtained along the coast of China in the 21 st century. Using the SRTM elevation data the submergence of coastal low land is calculated under the extreme water level with a 100-year retum period. The total flooding areas are 98.3× 10^3 and 104.9× 10^3 km2 for 2050 and 2080, respectively. For the three regions most vulnerable to extreme sea level rise, i.e., the coast of Bohai Bay, the Yangtze River Delta together with neighboring Jiangsu Province and northern Zhejiang Province, and the Pearl River Delta, the flooded areas are 5.0× 10^3, 64.1×10^3 and 15.3 × 10^3 km2 in 2050 and 5.2 × 10^3, 67.8×10^3 and 17.2 × 10^3 km2 in 2080, respectively.

Design Code Calibration of Offshore Platform Against Typhoon/Hurricane Attacks

Hurricanes Katrina and Rita resulted in the largest number of platforms destroyed and damaged in the history of Gulf of Mexico operations. With the trend of global warming, sea level rising and the frequency and intensity of typhoon increase. How to determine a reasonable deck elevation against the largest hurricane waves has become a key issue in offshore platforms design and construction for the unification of economy and safety. In this paper, the multivariate compound extreme value distribution （MCEVD） model is used to predict the deck elevation with different combination of tide, surge height, and crest height. Compared with practice recommended by American Petroleum Institute （API）, the prediction by MCEVD has probabilistic meaning and universality.