Trends in Extreme Mean Sea Level Quantiles from Satellite Altimetry

Satellite altimetry allows the study of sea-level long-term variability on a global and spatially uniform basis. Here quantile regression is applied to derive robust median regression trends of mean sea level as well as trends in extreme quantiles from radar altimetry time series. In contrast with ordinary least squares regression, which only provides an estimate on the rate of change of the mean of data distribution, quantile regression allows the estimation of trends at different quantiles of the data distribution, yielding a more complete picture of long-term variability. Trends derived from basin-wide averaged regional mean sea level time series are robust and similar for all quantiles, indicating that all parts of the data distribution are changing at the same rate. In contrast, trends are not robust and diverge across quantiles in the case of local time series. Trends are under- (over-)estimated in the western (eastern) equatorial Pacific. Furthermore, trends in the lowermost quantile (0.05) are larger than the median trend in the western Pacific, while trends in the uppermost quantile (0.95) are lower than the median trend in the eastern Pacific. These differences in trends in extreme mean sea level quantiles are explained by the exceptional effect of the strong 1997–1998 El Niño–Southern Oscillation (ENSO) event.     

Human impacts on tides overwhelm the effect of sea level rise on extreme water levels in the Rhine–Meuse delta

With the aim to link tidal and subtidal water level changes to human interventions, 70 years of water level data for the Rhine–Meuse tidal river network is analysed using a variety of statistical methods. Using a novel parameterization of probability density functions, mean high and low water levels are examined, and extreme water levels are investigated by applying the combined Mann–Kendall and Pettitt tests to find trends and trend changes. Tidal water levels are studied based on harmonic analysis. Results show that the mean water levels throughout the system rise with the same pace as the mean sea level. However, high- and low water levels do not show the same increase, and the spatial variability in decadal trends in high- and low water levels is high. High water and low water extremes generally decrease. Both the extreme water level analysis and the harmonic analysis display significant trend breaks in 1970, 1981 and 1997. These breaks can be attributed to the closure of the Haringvliet estuary, the removal of sluices and the removal of a dam, respectively, which radically alter the tidal motion. These results demonstrate that the direct human influence on the tidal motion can overwhelm the effect of mean sea level rise on water level extremes.     

Extreme Statistics of Storm Surges in the Baltic Sea

Statistical analysis of the extreme values of the Baltic Sea level has been performed for a series of observations for 15–125 years at 13 tide gauge stations. It is shown that the empirical relation between value of extreme sea level rises or ebbs (caused by storm events) and its return period in the Baltic Sea can be well approximated by the Gumbel probability distribution. The maximum values of extreme floods/ebbs of the 100-year recurrence were observed in the Gulf of Finland and the Gulf of Riga. The two longest data series, observed in Stockholm and Vyborg over 125 years, have shown a significant deviation from the Gumbel distribution for the rarest events. Statistical analysis of the hourly sea level data series reveals some asymmetry in the variability of the Baltic Sea level. The probability of rises proved higher than that of ebbs. As for the magnitude of the 100-year recurrence surge, it considerably exceeded the magnitude of ebbs almost everywhere. This asymmetry effect can be attributed to the influence of low atmospheric pressure during storms. A statistical study of extreme values has also been applied to sea level series for Narva over the period of 1994–2000, which were simulated by the ROMS numerical model. Comparisons of the “simulated” and “observed” extreme sea level distributions show that the model reproduces quite satisfactorily extreme floods of “moderate” magnitude; however, it underestimates sea level changes for the most powerful storm surges.     

Les surcotes et les décotes marines à Brest, étude statistique et évolution

Sea surges (positive or negative) are short-period events (several hours to several days) among the most extreme oceanic phenomena resulting from climatic variability. A statistical study of hourly tide-gauge records at Brest does not allow any clear trend in long-term variations of these extreme sea levels to be detected. However, the frequency of extreme positive sea surges has increased recently (1953–1994), whereas extreme and sub-extreme negative sea surges has decreased. Such trends for the highest values strengthen the prevalence of positive sea surges over negative ones. The general evolution appears to be organised around several time scales, with a strong interannual variability superimposed on periods of amplification or regression of decennial order.     

Spatial and temporal variability of coastal storms in the North Atlantic Basin

Over the past three to four decades, there has been a growing awareness of the important controls exerted by large-scale meteorological events on coastal systems. For example, definitive links are being established between short-term (timescales of 5–10 years) beach dynamics and storm frequency. This paper assesses temporal variability of coastal storms (both tropical and extratropical) and the wave climatology in the North Atlantic Basin (NAB), including the Gulf of Mexico. With both storm types, the empirical record shows decadal scale variability, but neither demonstrates highly significant trends that can be linked conclusively to natural or anthropogenic factors. Tropical storm frequencies have declined over the past two or three decades, which is perhaps related to recent intense and prolonged El Niños. Some forecasts predict higher frequencies of tropical storms like that experienced from the 1920s to the 1960s to occur in coming decades. Results from general circulation models (GCMs) suggest that overall frequencies of tropical storms could decrease slightly, but that there is potential for the generation of more intense hurricanes. These data have important implications for the short-term evolution of coastal systems.

There is strong suggestion that extratropical systems have declined overall over the past 50–100 years, but that there is an increase in frequency of very powerful storms, especially at higher latitudes. Both ENSO and the North Atlantic Oscillation (NAO) are shown to have associations with frequencies and tracking of these systems. These empirical results are in general agreement with GCM forecasts under global warming scenarios. Analyses of wave climatology in the NAB show that the last two to three decades have been rougher at high latitudes than several decades prior, but this more recent sea state is similar to conditions from about 100 years ago. The recent roughness at sea seems to be related to high NAO index values, which are also expected to increase with global warming. Thus, when coupled to an anticipated continued rise in global sea level, this trend will likely result in increasing loss of sediment from the beach-nearshore system resulting in widespread coastal erosion.     

Modeling erosion of sedimentary coasts in the western Russian Arctic

Morphodynamic modeling is employed in the present work to predict the long-term evolution (over the next 100 years) of typical sedimentary coasts in the western Russian Arctic. The studied objects are the coasts of Varandey (the Barents Sea), Baydaratskaya Bay and Harasavey (the Kara Sea). The model developed takes into account both the short-term processes (storm events) and long-term factors (for example, changes in sea level, inter-annual variations in gross sediment flux, lack or excess of sediment supply). Predicted and observed morphological changes in coastal profiles are shown to agree well for time scales ranging from weeks to decades. It is revealed that under given environmental conditions, the morphological evolution is strongly influenced by storm surges and associated wind-driven circulation. The water level gradient created by a surge generates a seaward flow at the bed. This outflow is shown to be an important destructive mechanism contributing to the erosion and recession of Arctic coasts. The rate of change is found to depend on both the exposure of the coast (relative to the direction of dominant winds) and its height above the sea. The open coast of Varandey is expected to retreat as much as 300–500 m over 100 years, while recession of the less exposed coasts of Baydaratskaya Bay would not exceed about 100 m/century. If long-term sediment losses are insignificant, the rate of erosion decays with time and the morphodynamic system may tend toward equilibrium. It is concluded that the expected relative sea-level rise (up to 1 m over the nearest 100 years) is non-crucial to the future coastal evolution if an erosion activity is already high enough.     

Variability of Sea Surface Heights in the Baltic Sea: An Intercomparison of Observations and Model Simulations

Sea level changes in the Baltic Sea are dominated by internal, short-term variations that are mostly caused by the ephemeral nature of atmospheric conditions over the Baltic area. Tides are small and their influence decreases from western parts of the Baltic Sea to the Baltic Proper. Superimposed to the large short-term sea level changes (up to few decimeters from day to day) are seasonal and interannual variations (centimeters to decimeters). This study focuses on the comparison of sea surface heights obtained from observations and from a high resolution oceanographic model of the Baltic Sea. From this comparison, the accuracy of the modeled sea surface variations is evaluated, which is a necessary precondition for the further use of the oceanographic model in geodetic applications. The model reproduces all observed Baltic sea level variations very reliably with an accuracy of 5 to 9 cm (rms) for short-term variations (up to 2 months) and 8 cm (rms) for long-term variations (>2 months). An additional improvement of the model can be attained by including long-period sea level variations of the North Sea. The model performs well also in the case of extreme sea level events, as is shown for a major storm surge that occurred at the southern coast of the Baltic Sea in November 1995.     

环日本岛沿岸海平面长期变化特征与机制的研究

利用环日本岛沿岸38个验潮站连续36 a的实测水位资料,分析了环日本岛沿岸平均海平面的长期变化特征,结果表明平均海平面的异常变化在1984年前后发生较大转折,近20多年来主要呈现持续上升趋势,部分站位在1997年前后也有较明显的下降趋势,表明海平面的长期变化中存在较长周期的波动情况。通过对所有验潮站的日平均海平面序列进行平均,发现与西北太平洋SST异常变化呈正相关,相关系数为0.908;与太平洋年代际变化(PDO)指数呈负相关,相关系数为-0.6;与西北太平洋风旋度场的异常变化呈正相关,相关系数为0.402。结果表明环日本岛沿岸平均海平面的长期变化受到海水热膨胀效应、太平洋年代际变化以及风应力引起的海水堆积和流失等因素的影响。同时,发现从2000年开始西北太平洋的SST开始下降,而平均海平面仍然在持续上升,其上升原因还需作进一步研究与探讨。     

江苏近岸海域水位变化特征分析

基于江苏沿海连云港、吕四两个测点的验潮站多年的观测资料以及AVISO卫星高度计资料,利用统计分析方法和潮汐调和分析方法研究江苏沿海地区的海洋水位变化特征。结果表明:江苏沿海海平面和潮差均呈上升趋势,海平面上升速度达3.35 mm/a,高于全球和区域海平面的上升速度;对采样间隔为1 h的潮位连续观测数据作调和分析,各验潮站主要半日分潮的振幅呈上升趋势,全日分潮的振幅呈下降趋势,S_a分潮的周期性变化与El Nino现象有关。     

Effect of Sea Level Variation on Calculation of Design Water Level

The long-term variation and seasonal variation of sea level have a notable effect on the calculation of engineering water level. Such an effect is first analyzed in this paper. The maximal amplitude of inter-annual anomaly of monthly mean sea level along the China coast is larger than 60 cm. Both the storm surge disaster and cold wave disaster are seasonal disasters in various regions, so the water level corresponding to the 1% of the cumulative frequency in the cumulative frequency curve of hourly water level data for different seasons in various sea areas is different from design water level, for example, the difference between them reaches maximum in June, July and August for northern sea area, and maximum in September, October and November for Southern China Sea. The hourly water level data of 19 gauge stations along the China coast are analyzed. Firstly, the annual mean sea level for every station is obtained; secondly, linear chan ging rates of annual mean sea level are obtained with the stochasti     

Effects of two decades of rising sea surface temperatures on sublittoral macrobenthos communities in Northern Ireland,UK

We examined whether two decades of rising sea surface temperatures have resulted in significant changes in the benthic community and frequency of occurrence of Northern and Southern species in three areas of Northern Ireland, using visual census data collected by SCUBA surveys undertaken during two periods: pre-1986 and post-2006. We found little evidence to suggest that rising sea surface temperatures have contributed to the changes in benthic assemblage structure between the pre-1986 and post-2006 surveys. However, there were slight but not significant declines in extreme Northern species at Rathlin Island, and increases in the mean number and frequency of occurrence of extreme Southern species in all three areas. There were also substantial declines in the spatial presence of 7 extreme Northern species and notable increases in distribution of 19 extreme Southern species. In contrast, there were no clear trends in the intermediate to Northern and intermediate to Southern species. These results suggest that rising sea surface temperatures have had significant impacts on the occurrence of rarer marine invertebrate species at the edges of their biogeographic range however the trends differed between areas in Northern Ireland.     

海平面上升、强台风和风暴潮对厦门海域极值水位的影响及危险性预估

气候变化背景下海平面上升、强台风和风暴潮对我国东南沿海地区的洪涝灾害影响日益严重,为应对气候变化的影响,本文以位于我国东南沿海的厦门地区为例,应用多种海洋大气观测资料和数理统计及模拟方法,分析了历史上9914号和1614号两次台风对厦门海域极端海面高度(极值水位)的影响,预估了未来海平面上升情景下厦门海域极值水位的变化...     

Effects of tropical cyclone paths and shelf bathymetry on inducement of severe storm surges in the Gulf of Thailand

The influences of tropical cyclone paths and shelf bathymetry on the inducement of extreme sea levels in a regional bay are investigated. A finite volume coastal ocean model(FVCOM) has been configured for the Gulf of Thailand-Sunda Shelf. A parametric wind model is used to drive the FVCOM. The contributions of the tropical cyclone characteristics are determined through a scenario-based study. Validation based on a historical extreme sea level event shows that the model can resolve the oscillation mechanism well. The intensification of severe storm surges in the region highly depends on four factors including phase propagation of the storm surge wave determined by the landfall position, funnel effect caused by locality of the coastline, and shelf bathymetry determined by the state of mean sea level and coastline crossing angle of the storm path. The coexistence of these factors can cause particular regions e.g. the Surat Thani Bay, inner Gulf of Thailand and Ca Mau Peninsular to experience a larger surge magnitude. These areas are found to be highly related to monsoon troughs that develop during the onset and early northeastern monsoon season(October–November).     

Sea level change along the coast of China relative to the isostatic datum

On the basis of the analyses of significant periods for the sea level observation data taken from recent several decades at 12 tide stations, the monthly mean sea level observations are fitted by a model of linear trend of sea level change superimposed with several variations of different fixed periods. The trends of sea level relative changes and their errors are estimated by the LS method. The results are reduced to the isostatic datum proposed and established in the paper (Huang et al. , 1991, Seismology and Geology , 1, 1-15). The trends of sea level changes in the near future along the coast of China are studied. It is pointed out that the general trend of the sea level change along the coast of China is going up slowly and the rate of the change is not the same in different segments of the coasts. In a few segments, the sea level is even relatively going down. The numerical results given in this paper provide a basis for the predictions of the future sea level changes and their effects.     

Sea Levels and Coastal Inundation Due to Tropical Cyclones in Indian Coastal Regions of Andhra and Orissa

Coastal inundation associated with extreme sea levels is the main factor which leads to the loss of life and property whenever a severe tropical cyclonic storm hits the Indian coasts. The Andhra and Orissa coasts are most vulnerable for coastal inundation due to extreme rise in sea levels associated with tropical cyclones. Loss of life may be minimized if extreme sea levels and associated coastal flooding is predicted well in advance. Keeping this in view, location specific coastal inundation models are developed and applied for the Andhra and Orissa coasts of India. Several numerical experiments are carried out using the data of past severe cyclones that struck these regions. The simulated inland inundation distances are found to be in general agreement with the reported flooding.     

Spatial Variation of Sea Level Trend Along the Bangladesh Coast

The Bangladesh coast is threatened by rising sea level due to various factors. The results based on the analysis of past 22 years of tidal data of the Bangladesh coast reveal that the annual mean tidal level in the eastern Bangladesh coast is rising at an alarmingly high rate of 7.8 mm/year, which is almost twice the observed rate in the western region. This type of sea level trend seems to be the result of changing local conditions like increased precipitation and land subsidence during the recent decades. It seems that the higher rate of land subsidence in the eastern Bangladesh coast is the main causative factor for the steeper sea level trends there. The differential sea level trends show that the subsidence component in the sea level rise may be as high as 4 mm/year in the eastern Bangladesh coast. However, this needs to be verified with actual geological observations.     

Shifts in multi-decadal sea level trends in the East/Japan Sea over the past 60 years

Data derived from altimetry shows that since 1993 the mean sea level over the East /Japan (EJS) Sea is increasing at a rate of ~3 mm/year, but tide gauge records indicate that a multidecadal reversal trend occurred prior to the early 1980s. We here characterize and quantify the multi-decadal trend of mean sea level in the EJS from the reconstructed sea levels and the in-situ ocean profiles over the past 60 years. Our analysis shows that sea level trends have undergone a shift, revealing a declining trend before the early 1980s, followed by a rising trend from the early 1980s onward with a near basin-wide sea level fluctuation. The trend reversal strongly corresponds to changes in the upper-ocean heat content over the EJS, revealing a negative correlation with the Pacific Decadal Oscillation (PDO) index that correlates negatively with wind stress curl (WSC) in the subtropical North Pacific. The PDO-related WSC, which changes the transport of the western boundary current in the subtropical gyre, may account for the observed trend reversal in the EJS sea level on a multi-decadal time scale.     

Spatial Variation of Sea Level Trend Along the Bangladesh Coast

The Bangladesh coast is threatened by rising sea level due to various factors. The results based on the analysis of past 22 years of tidal data of the Bangladesh coast reveal that the annual mean tidal level in the eastern Bangladesh coast is rising at an alarmingly high rate of 7.8 mm/year, which is almost twice the observed rate in the western region. This type of sea level trend seems to be the result of changing local conditions like increased precipitation and land subsidence during the recent decades. It seems that the higher rate of land subsidence in the eastern Bangladesh coast is the main causative factor for the steeper sea level trends there. The differential sea level trends show that the subsidence component in the sea level rise may be as high as 4 mm/year in the eastern Bangladesh coast. However, this needs to be verified with actual geological observations.     

Sea Levels and Coastal Inundation Due to Tropical Cyclones in Indian Coastal Regions of Andhra and Orissa

Coastal inundation associated with extreme sea levels is the main factor which leads to the loss of life and property whenever a severe tropical cyclonic storm hits the Indian coasts. The Andhra and Orissa coasts are most vulnerable for coastal inundation due to extreme rise in sea levels associated with tropical cyclones. Loss of life may be minimized if extreme sea levels and associated coastal flooding is predicted well in advance. Keeping this in view, location specific coastal inundation models are developed and applied for the Andhra and Orissa coasts of India. Several numerical experiments are carried out using the data of past severe cyclones that struck these regions. The simulated inland inundation distances are found to be in general agreement with the reported flooding.     

热带西太平洋水位的年际变化与ENSO事件

根据美国ＴＯＧＡ水位中心所提供的１９７５—１９８８年水位月平均资料，分析、讨论了热带西太平洋水位的年际变化特征，特别是与ＥＮＳＯ事件有关的低水位现象。此外，还重点叙述了１９８６—１９８７年ＥＮＳＯ事件中水位沿经向和赤道剖面的变化，以及与此有关的赤道流系的变化。文中还定性地讨论了赤道开尔文波沿赤道剖面的传播特性。