Changes In Extreme Sea Levels Research Articles

Assessing changes in extreme sea levels along the coast of China

AbstractHourly tide‐gauge data along the coast of China are used to evaluate changes in extreme water levels in the past several decades. Mean sea level, astronomical tide, nontidal component and the tide‐surge interaction was analyzed separately to assess their roles in the changes of extreme sea levels. Mean sea level at five tide gauges, Kanmen, Keelung, Zhapo, Xiamen and Quarrybay, show significant increasing trends during the past decades (1954–2013) with a rate of about 1.4–3.5 mm/yr. At Keelung, Kaohsiung and Quarrybay the mean high waters increased during 1954–2013 with a rate from 0.6 to 1.8 mm/yr, while the annual mean tidal range rose at the same time by 0.9 to 3.8 mm/yr. In terms of storm surge intensities, there is interannual variability and decadal variability but five tide gauges show significant decreasing trends, and three gauges, at Keelung, Xiamen and Quarrybay, exhibited significant increases of extreme sea levels with trends of 1.5–6.0 mm/yr during 1954–2013. Significant tide‐surge interactions were found at all 12 tide gauges, but no obvious change was found during the past few decades. The changes in extreme sea levels in this area are strongly related to the changes of mean sea levels (MSL). At gauges, where the tide‐surge interaction is large, the astronomic tides are also an important factor for the extreme sea levels, whereas tide gauges with little tide‐surge interaction, the changes of wind driven storm surge component adds to the change of the extreme sea levels.

Long‐term variations in global sea level extremes

AbstractDecadal to multidecadal variations in sea level extremes unrelated to mean sea level changes have been investigated using long tide gauge records distributed worldwide. A state space approach has been applied that provides robust solutions and uncertainties of the time evolving characteristics of extremes, allowing for data gaps and uneven sampling, both common features of historical sea level time series. Two different models have been formulated for the intensity and for the occurrence of extreme sea level events and have been applied independently to each tide gauge record. Our results reveal two key findings: first, the intensity and the frequency of occurrence of extreme sea levels unrelated to mean sea level vary coherently on decadal scales in most of the sites examined (63 out of 77) and, second, extreme sea level changes are regionally consistent, thus pointing toward a common large‐scale forcing. This variability of extremes associated with climate drivers should be considered in the framework of climate change studies.

Inverted barometer contributions to recent sea level changes along the northeast coast of North America

AbstractRegional sea level (SL) changes reflect dynamic and isostatic ocean effects. Recent works have interpreted accelerated and extreme SL changes along the northeast coast of North America primarily in terms of dynamic changes; however, dedicated study of isostatic changes related to surface atmospheric pressure loading—the inverted barometer (IB) effect—has been lacking. This investigation uses five different atmospheric pressure products to analyze the influence of the IB effect on annual mean SL from tide gauge records. The IB effect explains ∼25% of interannual SL variance and accounts for ∼50% of the magnitude of a recent extreme event of SL rise along Atlantic Canada and New England. Estimated IB effects also amount to ∼10–30% of recent multidecadal SL accelerations over the Mid‐Atlantic Bight and Southern New England. These findings reiterate the need for careful estimation and removal of isostatic effects for studies of dynamic SL.

Changes in extreme sea-levels in the Baltic Sea

In a climate change context, changes in extreme sea-levels rather than changes in the mean are of particular interest from the coastal protection point of view. In this work, extreme sea-levels in the Baltic Sea are investigated based on daily tide gauge records for the period 1916–2005 using the annual block maxima approach. Extreme events are analysed based on the generalised extreme value distribution considering both stationary and time-varying models. The likelihood ratio test is applied to select between stationary and non-stationary models for the maxima and return values are estimated from the final model. As an independent and complementary approach, quantile regression is applied for comparison with the results from the extreme value approach. The rates of change in the uppermost quantiles are in general consistent and most pronounced for the northernmost stations.

The impact of future changes in weather patterns on extreme sea levels over southern Australia

This study first compares two methods by which the global, variable resolution Cubic Conformal Atmospheric Model (CCAM) is forced by reanalysis over Australia. The methods are the spectral nudging and bias‐corrected sea surface temperature (SST) forcing. Surface winds and sea level pressure are compared since these influence coastal sea levels. SST forcing was found to better preserve the mean and standard deviation of these quantities. Second, a hydrodynamic model is used to model sea levels over southern Australia over 1980–1999 and 2080–2099 to investigate how changes in weather patterns affect extreme sea levels. Forcing from one Global Climate Model (GCM) and two CCAM simulations in which CCAM was used to downscale two GCMs over Australia with bias‐corrected SST forcing (including the GCM considered in this study) were used. While there are differences in the spatial patterns of change between seasons over the modeled coastline between the three models, extreme sea levels were mostly lower in the future period over the southern mainland coastline from autumn to spring due to reduced westerlies in the climate models. The sea level changes around Tasmania varied from positive to negative depending on the model and season. The projected extreme sea level changes were within 10 cm of current climate values. This suggests that over southern Australia extreme sea level changes will be dominated by changes in mean sea level due to thermal expansion and ice sheet and glacier melt rather than changes in weather patterns.

Evidence for Century-Timescale Acceleration in Mean Sea Levels and for Recent Changes in Extreme Sea Levels

Two of the most important topics in Sea Level Science are addressed in this paper. One is concerned with the evidence for the apparent acceleration in the rate of global sea level change between the nineteenth and twentieth centuries and, thereby, with the question of whether the twentieth century sea level rise was a consequence of an accelerated climate change of anthropogenic origin. An acceleration is indeed observed in both tide gauge and saltmarsh data at different locations around the world, yielding quadratic coefficients ‘c’ of order 0.005 mm/year2, and with the most rapid changes of rate of sea level rise occurring around the end of the nineteenth century. The second topic refers to whether there is evidence that extreme sea levels have increased in recent decades at rates significantly different from those in mean levels. Recent results, which suggest that at most locations rates of change of extreme and mean sea levels are comparable, are presented. In addition, a short review is given of recent work on extreme sea levels by other authors. This body of work, which is focused primarily on Europe and the Mediterranean, also tends to support mean and extreme sea levels changing at similar rates at most locations.

Carboniferous–Permian carbon isotope stratigraphy of successions from China (Yangtze platform), USA (Kansas) and Russia (Moscow Basin and Urals)

The Pennsylvanian and Early Permian were times of extreme sea-level changes of > 100 to perhaps up to 200 m. For example, glacio-eustatic sea-level changes are well documented from the US Midcontinent, Moscow Basin and Yangtze Platform, where more than 100 stacked subtidal to supratidal sequences have been described. In contrast, carbonates developed in the Ural Mountains and South Guizhou of the Yangtze Platform were deposited in ramp and slope settings. δ 13C values of whole rock samples from the US Midcontinent and Moscow Basin were intensively affected by diagenesis. Only well-preserved brachiopod shells maintained their original carbon isotope ratios. In contrast, limestones deposited in the deeper water slope environments were not affected by meteoric diagenesis and are interpreted to have mainly retained their carbon isotope ratios. Mean δ 13C values of slope carbonates of the Yangtze Platform increase from about 3‰ during the Viséan and Serpukhovian to 5‰ at the Carboniferous–Permian boundary and decrease to values around 2‰ in the early Kungurian. This positive δ 13C excursion coincides with low δ 13C values in the Yangtze Platform successions, which were reset by meteoric diagenesis. The highest δ 13C values recorded in the slope succession coincide with the inferred maximum glaciation that caused pronounced sea-level lowstands. Short-lived, but significant negative δ 13C excursions in the Chinese slope succession are interpreted to reflect changes in ocean circulation due to sea-level rises which caused enhanced production and/or preservation of organic matter which influenced the subsequent early diagenetic cementation.

Interpreting Century-Scale Changes in Southern North Sea Storm Surge Climate Derived from Coupled Model Simulations

Abstract This paper describes numerical experiments using a climate–storm surge simulation system for the coast of the United Kingdom, with a particular focus on the southern North Sea and the Thames estuary in southeastern England. Time series of surges simulated in the southern North Sea by a surge model driven by atmospheric data from a regional climate model and surges simulated by the same surge model driven by atmospheric data from a global climate model are compared. A strong correspondence is demonstrated, and a linear scaling factor relating them is derived. This factor varies slowly with location. Around the Thames estuary, extreme surges are compared in the same way, and the linear scaling factor for the extremes is found to be similar to that for the full time series. The authors therefore assert that in seeking significant trends in surge at this location using this model arrangement, the regional model downscaling stage could be avoided, if observations were used to establish a suitable scaling factor for each location. The influence of the tide–surge phase relationship is investigated, and extreme sea levels at the mouth of the River Thames from regional-model-driven simulations are compared to the extreme event of 1953. Although the simulated levels are slightly lower, they are found to be comparable given the observational uncertainty. The assumption that time-mean sea level changes can be added linearly to surge changes is investigated at this location for large changes in time-mean sea level. The authors find that the primary effect of such an increase is on the speed of propagation of tide and surge, supporting the case for a simple linear addition of mean and extreme sea level changes.

Estimating 21st century changes in extreme sea levels around Western Australia

Extreme sea levels are likely to increase in the future with an expected accelerated rise in mean sea level and through possible changes in storminess. Society is becoming more vulnerable to extreme sea levels due to considerable growth in human populations and economy at the coastal zone and this is particularly true for Western Australia, the fastest growing Australian state or region. This paper describes a novel approach used to estimate future changes in extreme sea level around the southwest coastline of Western Australia. Probabilities of extreme sea level for the present climate have been estimated using a 60 year hindcast of sea levels. The impact of climate change has been explored by adding a range of mean sea level rise projections to these probabilities. Estimates of possible future changes in recurrence intervals every decade over the 21st century are presented, showing that climate change has the potential to significantly reduce current average recurrence intervals and that the amount of reduction varies significantly around the coastline.

Assessing changes in extreme sea levels: Application to the English Channel, 1900–2006

A recently extended and spatially rich English Channel sea level dataset has been used to evaluate changes in extreme still water levels throughout the 20th century. Sea level records from 18 tide gauges have been rigorously checked for errors and split into mean sea level, tidal and non-tidal components. These components and the interaction between surge and tide have been analysed separately for significant trends before determining changes in extreme sea level. Mean sea level is rising at 0.8–2.3 mm/year, depending on location. There is a small increase (0.1–0.3 mm/year) in the annual mean high water of astronomical tidal origin, relative to mean sea level, and an increase (0.2–0.6 mm/year) in annual mean tidal range. There is considerable intra- and inter-decadal variability in surge intensity with the strongest intensity in the late 1950s. Storm surges show a statistically significant weak negative correlation to the winter North Atlantic Oscillation index throughout the Channel and a stronger significant positive correlation at the boundary with the southern North Sea. Tide–surge interactions increase eastward along the English Channel, but no significant long-term changes in the distribution of tide–surge interaction are evident. In conclusion, extreme sea levels increased at all of the 18 sites, but at rates not statistically different from that observed in mean sea level.