Increase In Mean Sea Level Research Articles

Loss of reef roughness increases residence time on an idealized coral reef

Through idealized, numerical models this paper investigates flows on a reef geometry which has received significant attention in the literature; a shallow, fringing reef with deeper, shore-ward pools or lagoons. Given identical model geometries and varying only reef flat drag coefficients between model runs (C_D = [0.001,0.005,0.01,0.05,0.1]), two distinct circulation patterns emerge. One is related to low reef water levels and high roughness, and efficiently flushes the entire reef system resulting in low residence times (an ‘open reef’). The other is related to high reef water levels and low roughness, and in spite of the development of an offshore undertow, this dynamic is inefficient at flushing the reef-pool system and facilitating exchange flow with offshore waters (a ‘closed reef’). This paper shows that even given indistinguishable geometry and offshore conditions, this information is insufficient to predict reef dynamics, and suggests that reef roughness (and thus reef health) plays a comparable role in determining circulation patterns and residence times. Furthermore, a transition from open to closed or vice versa caused by e.g., a loss of reef roughness or increase in mean sea level could have implications for transport and mixing of nutrients and water masses, as well as larval dispersal.

Predicting coastal inundation triggered by the oceanic forcing across Jakarta Bay

Coastal inundation becomes a severe hazard to many world’s cities near shorelines. A recent publication by the Intergovernmental Panel on Climate Change (IPCC) in 2021 projected the increase in mean sea level and the probability of extreme waves in the future that would add more pressure to the cities like Jakarta, Indonesia. Hence, the estimations of the region’s vulnerability due to the hazard are critical steps for designing the adaptation measures. The study is aimed to spatially estimate the future coastal flooding in Jakarta Bay caused by oceanic forcing under the IPCC 2021 scenarios, including the High Highest Water Level (HHWL), the predicted sea level rise by 50 years, the extreme wave setup, and the infragravity (IG) waves. The spatial inundation is generated by projecting the estimated total water level to the Jakarta region’s Digital Surface Model (DSM) and further overlaid on the rectified Google Earth image. The result shows that the increase in water level due to climate change may reach ~1.8 m, increasing the spatial inundation area around the Jakarta shoreline by 37 %. Considering the severe impacts of the projected inundation, the decision-makers need to focus on adaptation efforts soon.

Sea-level rise in Denmark: paleo context, recent projections and policy implications

We present the most recent Intergovernmental Panel on Climate Change Sixth Assessment Report (AR6) sea-level projections for four Danish cities (Aarhus, Copenhagen, Esbjerg and Hirtshals) under the Shared Socioeconomic Pathway (SSP) family of climate scenarios. These sea-level changes projected over the next century are up to an order of magnitude larger than those observed over the previous century. At these cities, year 2150 sea-level changes of between 29 and 55 cm are projected under the very low emissions scenario (SSP1-1.9), while changes of between 99 and 123 cm are projected under the very high emissions scenario (SSP5-8.5). These differences highlight the potentially significant impact of remaining opportunities for climate change mitigation. Due to this increase in mean sea level, the mean recurrence time between historically extreme events is expected to decrease. Under the very high emissions scenario, the historical 100-year storm flood event will become a 1- to 5-year event at most Danish harbours by 2100. There is considerable uncertainty associated with these sea-level projections, primarily driven by uncertainty in the future evolution of the Antarctic ice sheet and future sterodynamic changes in ocean volume. The AR6 characterises collapse of the West Antarctic ice sheet as a low-probability but high-impact event that could cause several metres of sea-level rise around Denmark by 2150. In climate adaptation policy, the scientific landscape is shifting fast. There has been a tremendous proliferation of diverse sea-level projections in recent years, with the most relevant planning target for Denmark increasing c. 50 cm in the past two decades. Translating sea-level rise projections into planning targets requires value judgments about acceptable sea-level risk that depend on local geography, planning timeline and climate pathway. This highlights the need for an overarching national sea-level adaptation plan to ensure municipal plans conform to risk and action standards.

Relationships between ecosystem properties and sea-level rise vulnerability of tidal wetlands of the U.S. Mid-Atlantic.

Tidal wetlands in the Mid-Atlantic, USA, are experiencing high rates of relative sea level rise, and it is unclear whether they will be resilient in the face of future flooding increases. In a previous study, we found 80% of our study areas in tidal freshwater and salt marshes in the Delaware Estuary and Barnegat Bay had elevation change rates lower than the 19-year increase in mean sea level. Here, we examine relationships between marsh elevation dynamics and abiotic and biotic parameters in order to assess their utility as indicators of vulnerability to relative sea level rise. We further apply a range of marsh vulnerability indicators including elevation change rates to evaluate their ability to corroborate marsh habitat change over the last 30years. Of the field measurements, soil bulk density and belowground plant biomass were among the strongest predictors of elevation change and accretion dynamics across all marsh types and settings. Both tidal freshwater and salt marshes tended to have higher rates of elevation increase and surface accretion in areas where soil bulk density and live belowground biomass were higher. Nine of the ten marshes experienced a net loss of area from the 1970s to 2015 ranging from 0.05 to 14%. Although tidal freshwater marshes were low in elevation and experienced variable elevation change rates, marsh area loss was low. Conversely, salt marshes closest to the coast and perched high in the tidal frame with a higher degree of human modification tended to experience the greatest marsh loss, which incorporated anthropogenic impacts and edge erosion. Thus, our regional assessment points to the need for a comprehensive understanding of factors that influence marsh resilience including human modifications and geomorphic settings.

Coastal Floods Induced by Mean Sea Level Rise—Ecological and Socioeconomic Impacts on a Mesotidal Lagoon

Coastal floods are currently a strong threat to socioeconomic activities established on the margins of lagoons and estuaries, as well as to their ecological equilibrium, a situation that is expected to become even more worrying in the future in a climate change context. The Ria de Aveiro lagoon, located on the northwest coast of Portugal, is not an exception to these threats, especially considering the low topography of its margins which has led to several flood events in the past. The growing concerns with these regions stem from the mean sea level (MSL) rise induced by climate changes as well as the amplification of the impacts of storm surge events, which are predicted to increase in the future due to higher mean sea levels. Therefore, this study aims to evaluate the influence of MSL rise on the inundation of Ria de Aveiro habitats and to assess the changes in inundation patterns resulting from frequent storm surges (2-year return period) from the present to the future, assessing their ecological and socioeconomic impacts. For this, a numerical model (Delft3D), previously calibrated and validated, was used to simulate the lagoon hydrodynamics under different scenarios combining MSL rise and frequent storm surge events. The numerical results demonstrated that MSL rise can change the vertical zonation and threaten the local habitats. Many areas of the lagoon may change from supratidal/intertidal to intertidal/subtidal, with relevant consequences for local species. The increase in MSL expected for the end of the century could make the lagoon more vulnerable to the effect of frequent storm surges, harming mostly agricultural areas, causing great losses for this sector and for many communities who depend on it. These extreme events can also affect artificialized areas and, in some cases, endanger lives.

Wave driven Setup across the North Coast Region of West Java

Wave energy dissipation on the surf zone is compensated with the increase of mean sea level, the so-called wave setup, within the area. This study used the numerical model Delft3D to investigate the dynamics of setup across the north coast region of West Java (Losari to Indramayu) influenced by monsoon variations. The wave forcing was obtained from previous field studies on Cirebon coastal region. The waves within the region were largely dissipated far from the coastline, mainly at the area between Babakan and Karangampel, due to the gentle slope of the North coast of Java. The waves approaching the shoreline were mainly influenced by the east monsoon associated with the longer fetch from that direction. The wave setup varied from ~0.03 to 0.15 m, with the maximum setup occurred near the coastline of the east (Losari) and west (Indramayu) parts of the model domain that consisted of steeper slopes. This, potentially inducing severe coastal inundation that became a serious problem across the coastlines. Meanwhile, the setup near the coastline of the middle area of the domain (Babakan to Karangampel) was very weak, which was correlated to the larger wave dissipation within the offshore area of that region.

Shoreline Dynamics in East Java Province, Indonesia, from 2000 to 2019 Using Multi-Sensor Remote Sensing Data

Coastal regions are one of the most vulnerable areas to the effects of global warming, which is accompanied by an increase in mean sea level and changing shoreline configurations. In Indonesia, the socioeconomic importance of coastal regions where the most populated cities are located is high. However, shoreline changes in Indonesia are relatively understudied. In particular, detailed monitoring with remote sensing data is lacking despite the abundance of datasets and the availability of easily accessible cloud computing platforms such as the Google Earth Engine that are able to perform multi-temporal and multi-sensor mapping. Our study aimed to assess shoreline changes in East Java Province Indonesia from 2000 to 2019 using variables derived from a multi-sensor combination of optical remote sensing data (Landsat-7 ETM and Landsat-8 OLI) and radar data (ALOS Palsar and Sentinel-1 data). Random forest and GMO maximum entropy (GMO-Maxent) accuracy was assessed for the classification of land and water, and the land polygons from the best algorithm were used for deriving shorelines. In addition, shoreline changes were quantified using Digital Shoreline Analysis System (DSAS). Our results showed that coastal accretion is more profound than coastal erosion in East Java Province with average rates of change of +4.12 (end point rate, EPR) and +4.26 m/year (weighted linear rate, WLR) from 2000 to 2019. In addition, some parts of the shorelines in the study area experienced massive changes, especially in the deltas of the Bengawan Solo and Brantas/Porong river with rates of change (EPR) between −87.44 to +89.65 and −18.98 to +111.75 m/year, respectively. In the study areas, coastal erosion happened mostly in the mangrove and aquaculture areas, while the accreted areas were used mostly as aquaculture and mangrove areas. The massive shoreline changes in this area require better monitoring to mitigate the potential risks of coastal erosion and to better manage coastal sedimentation.

MAPEAMENTO DA LINHA DE COSTA E AVALIAÇÃO DA VULNERABILIDADE E SUSCEPTIBILIDADE À EROSÃO COSTEIRA ENTRE A FOZ DO RIO SÃO JOÃO E A FOZ DO RIO UNA – CABO FRIO/RJ

O presente trabalho trata de uma avaliação da vulnerabilidade e susceptibilidade à erosão costeira através do uso de geoindicadores e do mapeamento da linha de costa entre a foz do rio São João e a do rio Una no município de Cabo Frio (RJ). Devido à ocorrência de eventos com ondas de alta energia, foram identificadas características erosivas em parte do arco praial, mesmo que tal praia não possua um quadro de erosão costeira constatada. A metodologia adotada envolve o uso de geoindicadores para a análise de dois pontos no arco praial, através do uso de uma série temporal de fotografias aéreas e imagens de alta resolução(anos 1970, 2005 e 2018) para a classificação do uso do solo da orla marítima e vetorização da linha de costa em ambiente SIG. Os resultados mostram que o ponto localizado mais ao norte do arco praial possui uma alta vulnerabilidade e susceptibilidade à erosão costeira, enquanto no ponto mais ao sul há uma baixa vulnerabilidade e susceptibilidade. Havendo um alto crescimento urbano e a intensificação da ocupação na orla marítima, com construções próximas ao perfil dinâmico praial, esta passa a sofrer ataque direto das ondas de alta energia. Em meio às possíveis alterações no clima, projetadas em estudos recentes, com elevação no nível médio do mar, maior frequência de eventos extremos, aumento da potência das ondas e ocupação massiva dos ambientes costeiros, estudos que embasem o planejamento de ocupação e gestão da orla marítima fazem-se necessários.
 Palavras-chave: geoindicadores, praias arenosas, linha de costa, erosão costeira.

An Update on the Status of Mean Sea Level Rise around the Korean Peninsula

The threat of sea level rise to the heavily populated Korean Peninsula, which contains around 15,000 km of coastline bordering open sea margins, has profound and far reaching implications. This study updates and extends previous detailed studies with the addition of a further 2 years of data to the end of 2019, providing renewed robustness to the identification of emerging threats associated with sea level rise within the warming sea margins around the Korean Peninsula. The study analyzes tide gauge records and satellite altimetry around the Republic of Korea using enhanced time series analysis techniques to detect coastal vertical land motion and current rates of rise in mean sea level to augment planning, design and risk management activities. Despite fluctuations over time at each site, the highest “relative” mean sea level at each of the seven longest tide gauge records occurs in 2019, with weak evidence of an acceleration in the increase in mean sea level around the Republic of Korea. Trends in sea surface height from satellite altimetry across this region note two discreet areas east and west of the Korean Peninsula around 37.5° N (around Ulleungdo Island and in the Gyeonggi Bay region of the Yellow Sea), where rates of rise are well above the global average trend.

Is the Ocean Speeding Up? Ocean Surface Energy Trends

AbstractA recent paper by Hu et al. (https://doi.org/10.1126/sciadv.aax7727) has raised the interesting question of whether the ocean circulation has been “speeding up” in the last decades. Their result contrasts with some estimates of the lack of major trends in oceanic surface gravity waves and wind stress. In general, both the increased energy and implied power inputs of the calculated circulation correspond to a small fraction of the very noisy background values. An example is the implied power increase of about 3 × 108 W, as compared to wind energy inputs of order 1012 W. Here the problem is reexamined using a state estimate that has the virtue of being energy, mass, etc. conserving. Because it is an estimate over an entire recent 26-yr interval, it is less sensitive to the strong changes in observational data density and distribution, and it does not rely upon nonconservative “reanalyses.” The focus is on the energy lying in the surface layers of the ocean. A potential energy increase is found, but it is almost completely unavailable—arising from the increase in mean sea level. A weak increase in kinetic energy in the top layer (10 m) is confirmed, corresponding to an increase of order 1 cm s−1 yr−1 over 26 years. An estimate of kinetic energy in the full water column shows no monotonic trend, but the changes in the corresponding available potential energy are not calculated here.

Hurricane Risk Assessment of Petroleum Infrastructure in a Changing Climate

Hurricanes threaten the petroleum industry in the United States and are expected to be influenced by climate change. This study presents an integrated framework for hurricane risk assessment of petroleum infrastructure under changing climatic conditions, calculating risk in terms of monetary loss. Variants of two synthetic probabilistic storms and one historical storm (Hurricane Ike) are simulated using the SWAN+ADCIRC model, representing a range of potential scenarios of impacts of a changing climate on hurricane forward speed and sea-level rise given uncertainties in climate projections. Model outputs inform an infrastructure impact and cascading economic loss analysis that incorporates various sources of uncertainty to estimate five types of losses sustained by petroleum facilities in surge events: land value loss, process-unit damage loss, cost of spill clean-up and repair of aboveground storage tanks, productivity loss, and civil fines. The proposed risk assessment framework is applied as a case study to seven refineries along the Houston Ship Channel (HSC), a densely-industrialized corridor in Texas. The results reveal that either an increase in mean sea level or a decrease in storm forward speed increases the maximum water elevations in the HSC for storms that produce maximum wind setup in Galveston Bay (FEMA 33 and FEMA 36), resulting in larger economic loss estimates. The role of refinery features such as storage capacity and average elevation of the refinery and its critical equipment in the refinery response to hurricane hazards is studied, and the probability distribution of refinery total loss and the loss risk profile in different hurricane scenarios are discussed. Loss estimates are presented, demonstrating the effects of hurricane forward speed and sea level on the losses for the refineries as well as the HSC. Such a framework can enable hurricane risk assessment and loss estimation for petroleum infrastructure to inform future policies and risk mitigation strategies. Potential policy implications for a region like the HSC are highlighted herein as an illustration.

The impact of Sea level rise in the guadiana estuary

Understanding the impact of sea level rise on coastal areas is crucial as a large percentage of the population live on the coast. This study uses computational tools to examine how two major consequences of sea level rise: salt intrusion and an increase in water volume affect the hydrodynamics and flooding areas of a major estuary in the Iberian Peninsula. A 2D numerical model created with the software MOHID was used to simulate the Guadiana Estuary in different scenarios of sea level rise combined with different freshwater flow rates considering varying tidal amplitudes. An increase in salinity was found in response to an increase in mean sea level in both high and low freshwater flow rates at all areas around the estuary. An increase in flooding areas around the estuary was also positively correlated with an increase in mean sea level.

Modeling Floodplain Inundation, Circulation and Residence Time Under Changing Tide and Sea-Levels.

Sea-level rise will have unknown effects on the structure and function of valuable tidal freshwater floodplains. One reason for this knowledge gap is our poor constraint on the physical controls on complex floodplain inundation and circulation processes. Here, a high-resolution light detection and ranging (lidar) digital elevation model (DEM) is applied to fine-scale numerical simulations of flow and tracer exchange in a 0.43 km2 river floodplain in Southeast Florida, USA. The sequence of inundation and associated circulation patterns is assessed at 1-hour intervals of the rising and falling tide in the context of floodplain geomorphic structure. The depth averaged velocity vectors show concomitant flow divergence and convergence over small spatial scales, and this complexity arises from the submergence and emergence of subtle floodplain topography over the tidal cycle. Tracer exchange and associated residence times highlight the controls of floodplain topography on water storage at the end of the ebb cycle, or during low river stages. The effects of a 0.2 m and 0.5 m increase in mean sea-level on inundation extent and water retention times were also assessed. Percent change in inundated area and associated e-folding times reveal greater lateral inundation extent and a 20% increase in water retention times with up to a 0.5 m increase in mean sea-level. This work reveals the topographic influence on how, when, and where sea-level rise will impact the freshwater floodplain through increased hydro period and salt-water intrusion, and the importance of evaluating floodplain restoration benefits in the context of fine-scale surface flow processes and sea-level rise.

A Numerical Investigation on Tidally Induced Sediment Transport and Morphological Changes with Changing Sea Level in South-East England

The impact of tide-induced morphological changes and water level variations on the sediment transport in a tidally dominated system has been investigated using the numerical model Delft3D and South-East England as a test case. The goal of this manuscript is to explore the long-term changes in morphology due to sea level rise and the large-scale morphodynamic equilibrium of the South-East England. Our results suggest that the long term (century scale) tidally-induced morphological evolution of the seabed slows down in time and promotes a vanishing net transport across the large scale system. Century-scale morphologically updated simulations show that both morphological changes and net transport values tend to decrease in time as the system attains a dynamic equilibrium configuration. Results further suggest that the presence of a gradual increase in mean sea level accelerates the initial morphological evolution of the system whose morphological rate of change gradually attains, however, same plateau values as in the absence of sea level rise. Given the same base morphology, increasing water levels enhance residual currents and the net transport near the coastline; and vice-versa, decreasing sea levels minimize both residuals and net transport near the coastline. The areas that are more affected by, water level and morphological changes, are the ones where the net transport is the highest. This manuscript explores and allows extending the idea of morphodynamic equilibrium at a regional scale, larger than the one for which this concept has been generally explored i.e., estuarine scale.

INTERCONNECTIVITIES BETWEEN HAZARD, DAMAGE, AND SHORELINE TYPE: LESSONS LEARNED FROM HURRICANE IRMA’S IMPACT ON THE FLORIDA KEYS

The 2017 Atlantic hurricane season had 17 named storms, 10 hurricanes, and 6 major hurricanes, generating over 226 units of accumulated cyclone energy (ACE), a measure used by the National Oceanographic and Atmospheric Association (NOAA) that refers to the combined the intensity and duration of a hurricane. These statistics earned the hurricane season’s classification as “extremely active,” the most active since 2005. Preliminary estimates of damage due to Hurricanes Harvey, Irma, and Maria amount to over $200 billion dollars in the United States alone. Recent studies suggest that the frequency of these high intensity Category 4 and 5 hurricanes is increasing (e.g. Mendelsohn et al., 2012). The 2017 hurricane season may thus be representative of an expected season. Accounting for projected increases in mean sea level, storm impacts may be exacerbated in coastal regions. These trends emphasize the need for effective damage mitigation techniques that improve the robustness and resiliency of coastal communities. Structures must be designed to not only avoid wave and surge loads, but also resist these forces in the event of a wave impact. Furthermore, creative, cost-effective solutions are required to mitigate waves and surge before they reach developed coastal areas. Thus, engineers require a robust, science-based methodology for predicting details of wave propagation over land and inland effects to ensure life safety and reduce economic loss due to extreme events. While traditional engineering strategies (e.g. seawalls, bulkheads) have been used to prevent coastal erosion and mitigate inland effects of hurricane waves and surge, recent storm events have shown potential of nature and natural based features (e.g. dune vegetation, mangroves, wetlands, salt-marshes, coral reefs, and seagrass) to protect coastal structures during storm events.

THE RELATIVE CONTRIBUTION OF SEA LEVEL RISE AND STORM EROSION TO LONG TERM NET COASTLINE RECESSION

The potential Climate change (CC) impacts on coasts and associated socio-economic and environmental risks are widely recognised internationally. One of the most talked about CC impacts is coastline recession. Any increase in mean sea level is expected to result in an upward and landward shift of the entire active profile causing net coastline recession (Bruun, 1962). Another phenomenon that can result in net coastline recession is the cumulative effect of storm erosion. This is due to the hysteresis effect in the storm erosion/dune recovery cycle (Ranasinghe et al., 2012). But what causes more recession: storms or sea level rise? This is a commonly asked question, to which science-backed answers have not been presented to date. This paper addresses this question via the application of a physics based, probabilistic numerical model at a typical swell and storm beaches located in SE Australia and The Netherlands, respectively.

Practical tools for quantitative analysis of coastal vulnerability and sea level rise impacts—application in a Caribbean island and assessment of the 1.5 °C threshold

The quantitative analysis of hurricane impacts on coastal development in the Caribbean is surprisingly infrequent and many tools to assess physical vulnerability to sea level rise (SLR) are insufficient to evaluate risk in coastal areas exposed to wave attack during extreme events. This paper proposes a practical methodology to quantify coastal hazards and evaluate SLR impact scenarios in coastal areas, providing quantitative input for coastal vulnerability analysis. We illustrate the implementation of the proposed methodology with results from a site-specific analysis. We quantify how storm wave impacts penetrate farther inland and reach higher elevations for increasing SLR conditions. We also show that the increase in elevation of storm wave impacts is more than the nominal increase in mean sea level, and that elevation increase may be on the order of up to twice the nominal SLR. By developing design parameters for multiple scenarios, as opposed to the determination of a single SLR value for design established by consensus, this approach generates information that we argue encourages resilient design and embedding future adaptation in coastal design. We discuss how government planners and regulators, as well as real estate developers, lenders, and investors, can improve coastal planning and resilient design of coastal projects by using this approach.

Mass balance of the Antarctic Ice Sheet from 1992 to 2017.

The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992-2017 (5±46 billion tonnes per year) being the least certain.

Regional marine climate scenarios in the NE Atlantic sector close to the Spanish shores

We present an overview of the changes expected during the 21st century in key marine parameters (sea surface temperature, sea surface salinity, sea level and waves) in the sector of the NE Atlantic Ocean close to the Spanish shores. Under the A1B scenario, open-sea surface temperatures would increase by 1°C to 1.5°C by 2050 as a consequence of global ocean warming. Near the continental margin, however, the global temperature rise would be counteracted by an enhancement of the seasonal upwelling. Sea surface salinity is likely to decrease in the future, mainly due to the advection of high-latitude fresher waters from ice melting. Mean sea level rise has been quantified as 15-20 cm by 2050, but two contributions not accounted for by our models must be added: the mass redistribution derived from changes in the large-scale circulation (which in the NE Atlantic may be as large as 15 cm in 2050 or 35 cm by 2100) and the increase in the ocean mass content due to the melting of continental ice (for which estimates are still uncertain). The meteorological tide shows very small changes, and therefore extreme sea levels would be higher in the 21st century, but mostly due to the increase in mean sea level, not to an increase in the storminess. The wave projections point towards slightly smaller significant wave heights, but the changes projected are of the same order as the natural variability.

Long-term trends (1989-2013) in the seabird community breeding in the lagoon of Venice (Italy)

The community of seabirds breeding in the lagoon of Venice, one of the largest around the Mediterranean, was monitored over the 1989-2013 period. Six species have been recorded (<em>Larus michahellis, Chroicocephalus ridibundus, Larus melanocephalus, Sternula albifrons, Sterna hirundo, Sterna sandvicensis</em>). Over the study period, 346 colonies were surveyed; they were located on saltmarsh islets, dredge islands and other artificial sites, in descending order of importance. Beaches were used only at the beginning of the survey. About 4,900 pairs bred in the 2009-2013 years. The community has been always dominated by <em>L</em>. <em>michahellis</em>; in the 2009-2013, this species and <em>S. sandvicensis</em> comprised about 70% of the total. The longterm trends show moderate increase in the size of the whole community. Contrasting trends were observed in different species, with <em>L. michahellis</em>,<em> S. albifrons</em> and <em>S. sandvicensis</em> stable or increasing, whereas <em>C. ridibundus</em> and <em>S. hirundo</em> were declining. The number of pairs nesting on artificial sites increased over the last 15 years, while those on saltmarsh islets decreased correspondingly. This was possibly a response to the increase of mean sea level and storminess observed in the last twenty-five years. <em>S. albifrons</em> and <em>S. sandvicensis</em> populations reached national importance; the population of the latter species is noteworthy at a Mediterranean level.