The examination of surge-tide interaction at two ports on the central south coast of England

When only a few years of sea level observations are available to the coastal engineer concerned with the design and maintenance of coastal defences at a location, a method other than that of annual maxima analysis must be used for the estimation of the frequency of occurrence of exceptional high sea levels. The most attractive and suitable method is that of joint surge-tide probability analysis. Negligible surge-tide interaction at the location enables the simplest kinds of joint probability methods to be applied and investigated, but, if the tide and surge components cannot be regarded as independent, it does entail computations of increasing complexity and length whilst of diminishing accuracy. It is shown how a detailed tide and interaction analysis for two major ports in close proximity can reveal substantial differences in interaction behaviour and hence the applicability of joint probability methods.     

1982–2019年渤、黄海海洋热浪时空变化特征分析

基于1982–2019年美国国家海洋和大气管理局最优插值海表温度资料,运用多种统计方法分析了渤、黄海海洋热浪（频次、持续时间、强度）的时空分布特征及与之相关的环流背景。结果表明:（1）海洋热浪具有一定的区域性差异,更强、更持久和更多的海洋热浪多集中在渤海和北黄海海区;（2）近38年来,渤、黄海海洋热浪变化趋势也具有明显的区域性差异,频次、年平均持续时间、年平均平均强度和最大强度总体呈增多、增强趋势,但朝鲜半岛沿岸海域没有显著变化,这与该地区的平均海温变化密切相关;（3）根据日平均海表面温度将海洋热浪分为中等、强、严重和极端4种等级,结果表明,除极端海洋热浪外,其他3种不同等级海洋热浪发生频次和增长趋势均存在显著的地理差异,中等强度海洋热浪在渤、黄海所有区域均频次偏多且有显著的增加趋势,而强和严重海洋热浪主要集中在我国的渤海海域,但渤、黄海区域极端海洋热浪几乎没有发生;（4）就渤、黄海区域平均而言,38年间,共发生83次海洋热浪,平均每年2.2次;海洋热浪具有明显的季节差异,不同等级强度的海洋热浪的多发季节均在夏季;（5）合成分析结果表明,夏季渤、黄海海洋热浪与大气环流密切相关,当从高层到低层贝加尔湖区域上空表现为大范围的相当正压结构的暖性高压异常时,盛行的下沉运动和高空西北气流,带来了晴朗的天气和更多的地面净太阳短波辐射,有利于渤、黄海海洋热浪的形成和维持。     

The impact of sea level rise and climate change on inshore wave climate: A case study for East Anglia (UK)

In coastal areas, offshore wave propagation towards the shore is influenced by water depth variations, due to sea bed bathymetry, tides and surges. Considering implications of climate change both on atmospheric forcing and sea level rise, a simple methodology involving numerical modelling is implemented to compute inshore waves from 1960 to 2099. Simulations take into account five scenarios of linear sea level rise and one climatic scenario for storm surges and offshore waves. The methodology is applied to the East Anglia coast (UK). Extreme event analysis is performed to estimate climate change implication on inshore waves and the occurrence of extreme events. It is shown, for this coastal region, that wave statistics are sensitive to the trend in sea level rise, and that the climate change scenario leads to a significant increase of extreme wave heights in the northern part of the domain. For nearshore points, the increase of the mean sea level alters not only extreme wave heights but also the frequency of occurrence of extreme wave conditions.     

The 44-year Mediterranean HIPOCAS wind database: A useful tool to analyse offshore extreme wind events from a long-term regional perspective

Nowadays, many efforts are leading to use the high potential offshore wind energy resources. A detailed assessment of the offshore wind resources arises as a first-rate requirement. Most of such assessment is based on extreme offshore wind atlas generated mainly from global reanalysis and satellite data. Both sort of data show certain shortcomings related, among others, to coarse spatial resolution and time inhomogeneity issues, respectively. This snag seems to be crucial over areas such as the Mediterranean Basin, which is characterized by a complex land–sea distribution and a significant orography. The HIPOCAS Mediterranean long-term (1958–2001) wind database comes to overcome the aforementioned reanalysis shortcoming and provides a Mediterranean wind data set useful to perform extreme wind analysis. This contribution also deals with a statistical extreme wind analysis over the whole Mediterranean offshore areas. Extreme return periods and levels are obtained from annual maxima using a number of distributions. Additionally, an alternative regional statistical method based on regional L-moment statistics is also proposed. The regional technique is applied to reduce uncertainty and allows a higher number of measurements to be included in the analysis, using data from a homogeneous region instead of from a single location. The herein performed extreme wind analysis provides a detailed assessment of high wind offshore areas over the Mediterranean and constitutes a subject of great interest for evaluation of wind resources.     

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.     

Wave climate variability of Taiwan waters

Global sea surface wind field data derived from NCEP reanalysis were used in driving a SWAN wave model to reconstruct historical wave records from 1948 to 2008. The reconstructed wave data were compared and verified by the observation of the data buoys of the Central Weather Bureau and the Water Resources Agency, Taiwan, and the National Data Buoy Center/National Oceanic and Atmospheric Administration, United States. Over the past six decades, the wave climate in Taiwan waters has undergone considerable changes. The annual mean significant wave heights have reduced an average of 0.31 cm/year. Winter wave heights have gradually dropped 0.86 cm/year, which are related to the weakening of winter monsoons. Regarding the inter-annual wave climate variation, the influence of El Niño/southern oscillation was substantial; the wave heights increased in La Niña years and decreased in El Niño years. In the past 60 years, extreme wave events have been concentrated in two periods: 1967–1974 and 2000–2008. More severe extreme wave events occurred in the latter compared with the former, and all were induced by typhoons. A clear trend, in which the summer (winter) extreme wave events have increased (decreased) gradually, has been identified. The 1980s was the transition period. After the transition period, the annual occurrence of extreme wave events caused by typhoons exceeded those caused by an intense outbreak of winter cold surges, although the total number of the annual extreme wave events has not changed substantially.     

New estimates of annual sea level maxima in the Bristol Channel

Observed sea level maxima in the form of annual extremes have been analysed for 4 ports in the Bristol Channel. The data analysed has been extended to include levels recorded in December 1981, when previous estimates of maximum return levels were exceeded.     

Aerial radiometry of sea surface temperatures on the east coast,North Island,New Zealand

The results of two airborne radiometer surveys of sea surface temperatures carried out east of New Zealand on 11 March and 28 April 1969 are presented, discussed in terms of the known oceanic circulation in the region, and compared with the pattern of sea surface temperature derived from a shipboard survey east of New Zealand, 1–14 March 1969. Short‐term temperature variations may be almost as large as the extreme annual range of sea surface temperatures.     

最平滤波器在分析月平均潮位资料中的应用

应用数字滤波方法来消除验潮资料中的高频扰动而分离出海平面的趋势性变化，并设计了最平滤波器；对其幅频响应特性和相位特性的验证表明，最平滤波器的技术性能基本上是可靠的。应用最平滤波器对月平均验潮序列进行低通数字滤波，可以有效地消除验潮资料中的高频扰动，分离出低频变化。从数值计算过程、高频扰动机制及实测验潮资料的估算结果来看，低通数字滤波在确定海平面长期变化趋势中，对消除高频扰动的影响是非常重要而有效的。     

Numerical Simulation of Extreme Sea Levels Using Location Specific High Resolution Model for Gujarat Coast of India

Although the frequency of tropical cyclones is less in the Arabian sea compared to that of the Bay of Bengal, there are several severe tropical cyclones which caused extensive damage along the Gujarat coast. In view of the high tidal range in the funnel-shaped gulfs of the Khambhat and the Kachch, it is very useful to study the surge response in these regions. There is always a possibility of abnormal rise of sea level when the occurrence of surge coincides with high tide, which may eventually cause inundation of vast stretches of shallow coastal areas. In view of this, a location specific fine resolution model is developed for the Gujarat coast. The east-west and north-south grid distances for the model are 5.1 km and 5.2 km, respectively. Several numerical experiments are carried out to compute the extreme sea levels using the wind stress forcings representative of 1982, 1996, and 1998 cyclones, which crossed this region. The model-computed extreme sea levels are in good agreement with the available observations.     

Numerical Simulation of Extreme Sea Levels Using Location Specific High Resolution Model for Gujarat Coast of India

Although the frequency of tropical cyclones is less in the Arabian sea compared to that of the Bay of Bengal, there are several severe tropical cyclones which caused extensive damage along the Gujarat coast. In view of the high tidal range in the funnel-shaped gulfs of the Khambhat and the Kachch, it is very useful to study the surge response in these regions. There is always a possibility of abnormal rise of sea level when the occurrence of surge coincides with high tide, which may eventually cause inundation of vast stretches of shallow coastal areas. In view of this, a location specific fine resolution model is developed for the Gujarat coast. The east-west and north-south grid distances for the model are 5.1 km and 5.2 km, respectively. Several numerical experiments are carried out to compute the extreme sea levels using the wind stress forcings representative of 1982, 1996, and 1998 cyclones, which crossed this region. The model-computed extreme sea levels are in good agreement with the available observations.     

A comparison of the main methods for estimating probabilities of extreme still water levels

Sea-level return periods are estimated at 18 sites around the English Channel using: (i) the annual maxima method; (ii) the r-largest method; (iii) the joint probability method; and (iv) the revised joint probability method. Tests are undertaken to determine how sensitive these four methods are to three factors which may significantly influence the results; (a) the treatment of the long-term trends in extreme sea level; (b) the relative magnitudes of the tidal and non-tidal components of sea level; and (c) the frequency, length and completeness of the available data. Results show that unless sea-level records with lengths of at least 50 years are used, the way in which the long-term trends is handled in the different methods can lead to significant differences in the estimated return levels. The direct methods (i.e. methods i and ii) underestimate the long (> 20 years) period return levels when the astronomical tidal variations of sea level (relative to a mean of zero) are about twice that of the non-tidal variations. The performance of each of the four methods is assessed using prediction errors (the difference between the return periods of the observed maximum level at each site and the corresponding data range). Finally, return periods, estimated using the four methods, are compared with estimates from the spatial revised joint probability method along the UK south coast and are found to be significantly larger at most sites along this coast, due to the comparatively short records originally used to calibrate the model in this area. The revised joint probability method is found to have the lowest prediction errors at most sites analysed and this method is recommended for application wherever possible. However, no method can compensate for poor data.     

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.     

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.     

湄洲湾海雾的发生规律和成因分析

利用湄洲湾及近海3个气象站1974～2003年和1个气象站1985～2003年的地面观测资料,统计分析了湄洲湾海雾的天气气候特征.湄洲湾海雾具有明显的年际变化,而且季节差异显著,其中2～5月是海雾的盛季.初步分析了湄洲湾海雾的成因,归纳得出2～5月该海湾海雾生成前的3种环流天气形势:锋面型、入海高压后部型、高压底部型.在对海雾生成的水文气象要素分析的基础上,得出了2～5月海雾发生的一般规律,为海洋预报和服务提供一定的参考依据.     

Estimating extreme water level probabilities: A comparison of the direct methods and recommendations for best practise

Over the past five decades, several approaches for estimating probabilities of extreme still water levels have been developed. Currently, different methods are applied not only on transnational, but also on national scales, resulting in a heterogeneous level of protection. Applying different statistical methods can yield significantly different estimates of return water levels, but even the use of the same technique can produce large discrepancies, because there is subjective parameter choice at several steps in the model setup. In this paper, we compare probabilities of extreme still water levels estimated using the main direct methods (i.e. the block maxima method and the peaks over threshold method) considering a wide range of strategies to create extreme value dataset and a range of different model setups. We primarily use tide gauge records from the German Bight but also consider data from sites around the UK and Australia for comparison. The focus is on testing the influence of the following three main factors, which can affect the estimates of extreme value statistics: (1) detrending the original data sets; (2) building samples of extreme values from the original data sets; and (3) the record lengths of the original data sets. We find that using different detrending techniques biases the results from extreme value statistics. Hence, we recommend using a 1-year moving average of high waters (or hourly records if these are available) to correct the original data sets for seasonal and long-term sea level changes. Our results highlight that the peaks over threshold method yields more reliable and more stable (i.e. using short records leads to the same results as when using long records) estimates of probabilities of extreme still water levels than the block maxima method. In analysing a variety of threshold selection methods we find that using the 99.7th percentile water level leads to the most stable return water level estimates along the German Bight. This is also valid for the international stations considered. Finally, to provide guidance for coastal engineers and operators, we recommend the peaks over threshold method and define an objective approach for setting up the model. If this is applied routinely around a country, it will help overcome the problem of heterogeneous levels of protection resulting from different methods and varying model setups.     

渤、黄海冰情与华北地区降水关系的分析

本文利用北京1932～2000年逐月降水量资料、渤、黄海海冰资料及1951～2000年气候因子资料，运用相关分析方法对冬季渤、黄海冰情与华北地区降水的关系进行了探讨，研究结果表明：冰情与降水存在着条件相关，如果海冰冰级达到2.5级以上且冬季副高较前一年有增强趋势，年降水大于平均值的可能性很大。这一点是对华北降水进行预测的一个新发现，对华北年降水趋势预测有着积极的作用。根据冰情与副高可判断当年降水的趋势。     

黄河三角洲造陆速率对夏季风强度变化和人类活动的响应

以夏季风强度指数和年均气温作为反映气候变化的指数,以人类净引水量和流域水土保持面积作为反映人类活动变化的指标,并以黄河流域为例,研究了三角洲造陆对气候变化和人类活动的响应.研究表明,夏季风强度指数的变化可分为三个阶段:(1)在1951~1963年夏季风强度指数呈持续增强的变化趋势;(2)在1963~1965年夏季风强度指数呈突变式减弱;(3)在1966~2000年夏季风强度指数保持在较低的水平上,且呈缓慢减弱的趋势.年降水量变化与夏季风强度指数有同步关系.从1950到1970年的年均温度在波动中略呈降低趋势,然而从1970年开始年均温度在波动中具有持续上升的趋势.气候变化会导致入海泥沙通量的变化,并可能进一步导致三角洲造陆速率的变化.黄河三角洲造陆速率、入海泥沙通量在1952~1964年均呈增大的趋势,1964年后则呈减小的趋势,在总体上与夏季风强度指数的变化趋势相同.除了气候变化以外,流域水土保持和引水对三角洲造陆也有影响.多元回归分析表明,三角洲造陆速率随夏季风强度指数的减弱而减小,随年气温的升高而减小,随梯田林草面积的增加而减小,随年净引水量的增加而减小,同时还表明,夏季风强度指数、年均气温、水土保持措施面积和人类净引水量对三角洲造陆速率变化的贡献率分别为34.94%,3.80%,53.82%和7.44%.表示气候变化的两个变量的贡献率之和为38.7%,说明气候变化对黄河三角洲造陆过程的影响是不容忽视的.     

不同气候情景下中国滨海城市海岸极值水位重现期预估

气候变化背景下,海平面上升叠加台风—风暴潮、天文大潮等产生的海岸极值水位事件趋多增强,对我国滨海城市社会经济可持发展构成了严重威胁。为认识未来我国滨海城市海岸极值水位危害性（强度和频率）的变化,本文首先采用第五次国际耦合模式比较计划（CMIP5）数据,分析了不同气候情景下（RCP2.6, 4.5, 8.5,简称为RCPs）下,未来不同年代（2030年、2050年和2100年）我国滨海城市沿岸海平面变化幅度;其次,基于沿海验潮站的历史观测资料和文献数据,分析了未来热带气旋强度变化对海岸极值水位的影响;最后,利用皮尔逊Ⅲ型（P-Ⅲ）水文概率曲线方法,预估了不同气候（RCPs）情景下未来不同年代（2030年、2050年和2100年）我国9个滨海城市海岸极值水位重现期的变化。结果表明：（1）在不同气候情景下,我国滨海城市沿海平均海平面均呈现上升趋势,其中,到21世纪末,长三角地区沿海海平面上升幅度最大,上升速度比全国平均高出约30%;（2）热带气旋的强度与台风—风暴潮的增水幅度存在正相关关系。预计到21世纪末,热带气旋的整体强度很可能将增强,热带气旋引发的台风—风暴潮的增水幅度较当前很可能有明显提高。（3）未来我国滨海城市沿海极值水位将有显著增高的趋势,当前极值水位的重现期将明显缩短。到21世纪末,我国滨海城市当前百年一遇的极值水位,重现期几乎都将缩短至20年一遇以下,其中,大连、青岛、上海和厦门等城市海岸极值水位重现期很可能缩短为（或低于）1年一遇。本文虽在一定程度上反映了不同气候情景下海岸洪水危害性的变化,但对于未来热带气旋的变化及其影响的研究尚有待进一步深入。     

设计波高推算的一种新模型

考虑台风影响海域的设计波高,结合复合极值理论和最大熵原则,构造了1种新型的具有4个待定参量和1个台风频次参量的poisson-最大熵分布函数模型,并推导出求解参数的方程组,参数的数值解可通过年极值实测数据的期望、方差、偏度和峰度得到.以黄海某观测站26 a极值波高的实测数据为例计算了新模型中4个待定参量和多年一遇设计波高,并与传统常用计算方法得到的结果进行比较.比较表明,新模型相比传统方法具有一定的优势.