Climate change induced sea level rise will affect shallow estuarine habitats, which are already under threat from multiple anthropogenic stressors. Here, we present the results of modelling to predict potential impacts of climate change associated processes on seagrass distributions. We use a novel application of relative environmental suitability (RES) modelling to examine relationships between variables of physiological importance to seagrasses (light availability, wave exposure, and current flow) and seagrass distributions within 5 estuarine embayments. Models were constructed separately for Posidonia australis and Zostera muelleri subsp. capricorni using seagrass data from Port Stephens estuary, New South Wales, Australia. Subsequent testing of models used independent datasets from four other estuarine embayments (Wallis Lake, Lake Illawarra, Merimbula Lake, and Pambula Lake) distributed along 570 km of the east Australian coast. Relative environmental suitability models provided adequate predictions for seagrass distributions within Port Stephens and the other estuarine embayments, indicating that they may have broad regional application. Under the predictions of RES models, both sea level rise and increased turbidity are predicted to cause substantial seagrass losses in deeper estuarine areas, resulting in a net shoreward movement of seagrass beds. Seagrass species distribution models developed in this study provide a valuable tool to predict future shifts in estuarine seagrass distributions, allowing identification of areas for protection, monitoring and rehabilitation.
Sea-level Rise, Coastal Flooding, and Storm Events
The upland nature of the Scottish landscape means that much of the social and economic activity has a coastal bias. The importance of the coast is further highlighted by the wide range of ecosystem services that coastal habitats provide. It follows that the threat posed by coastal erosion and flooding has the potential to have a substantial effect on the socioeconomic activity of the whole country. Currently, the knowledge base of coastal erosion is poor and this serves to hinder the current and future management of the coast. To address this knowledge gap, two interrelated models have been developed and are presented here: the Underlying Physical Susceptibility Model (UPSM) and the Coastal Erosion Susceptibility Model (CESM). The UPSM is generated within a GIS at a 50 m2 raster of national coverage, using data relating to ground elevation, rockhead elevation, wave exposure and proximity to the open coast. The CESM moderates the outputs of the UPSM to include the effects of sediment supply and coastal defence data. When validated against locations in Scotland that are currently experiencing coastal erosion, the CESM successfully identifies these areas as having high susceptibility. This allows the UPSM and CESM to be used as tools to identify assets inherently exposed to coastal erosion, areas where coastal erosion may exacerbate coastal flooding, and areas are inherently resilient to erosion, thus allow more efficient and effective management of the Scottish coast.
There is a pressing need to assess resilience of coastal ecosystems against sea level rise. To develop appropriate response strategies against future climate disturbances, it is important to estimate the magnitude of disturbances that these ecosystems can absorb and to better understand their underlying processes. Hammocks (petenes) coastal ecosystems are highly vulnerable to sea level rise linked to climate change; their vulnerability is mainly due to its close relation with the sea through underground drainage in predominantly karstic soils. Hammocks are biologically important because of their high diversity and restricted distribution. This study proposes a strategy to assess resilience of this coastal ecosystem when high-precision data are scarce. Approaches and methods used to derive ecological resilience maps of hammocks are described and assessed. Resilience models were built by incorporating and weighting appropriate indicators of persistence to assess hammocks resilience against flooding due to climate change at “Los Petenes Biosphere Reserve”, in the Yucatán Peninsula, Mexico. According to the analysis, 25% of the study area is highly resilient (hot spots), whereas 51% has low resilience (cold spots). The most significant hot spot clusters of resilience were located in areas distant to the coastal zone, with indirect tidal influence, and consisted mostly of hammocks surrounded by basin mangrove and floodplain forest. This study revealed that multi-criteria analysis and the use of GIS for qualitative, semi-quantitative and statistical spatial analyses constitute a powerful tool to develop ecological resilience maps of coastal ecosystems that are highly vulnerable to sea level rise, even when high-precision data are not available. This method can be applied in other sites to help develop resilience analyses and decision-making processes for management and conservation of coastal areas worldwide.
Similar to several other countries in Europe, a policy debate has emerged in Flanders (Belgium) arguing that flood risks should no longer be tackled by water managers alone but should become a shared responsibility between water managers, other governmental actors and citizens. Hence, a form of ‘co-production’ is advocated, whereby both governmental and non-governmental actors participate in bringing flood risk management into practice. This new approach represents a remarkable break with the past, since flood management in Flanders is traditionally based on flood probability reduction through engineering practices. The intended shift in private-public responsibilities can thus be expected to challenge the existing flood policy arrangement. Based on quantitative and qualitative research, this paper compares the attitudes towards individual responsibilities in flood protection among public officials and residents of flood-affected areas in the flood-prone basin of the river Dender. We find that whereas most public officials are in favour of sharing flood risk responsibilities between authorities and citizens, the majority of residents consider flood protection as an almost exclusive government responsibility. We discuss the challenges this discourse gap presents for the pursuit of a co-produced flood risk management and how these can be addressed. It is argued that a policy of co-production should embrace a co-evolutionary approach in which input, output and throughput legitimacy become intertwined.
Wave extreme events can be understood as the combination of Storm-intensity, Directionality and Intra-time distribution. However, the dependence structure among these factors is still unclear. A methodology has been developed to model wave-storms whose components are linked together. The model is composed by three parts: an intensity module, a wave directionality module, and an intra-time distribution module. In the Storm-intensity sub-model, generalized Pareto distributions and hierarchical Archimedean copulas have been used to characterize the storm energy, unitary energy, peak wave-period and duration. In the Directionality and Intra-time sub-models, the wave direction (at the peak of the storm) and the storm growth–decay rates are linked to the variables from the intensity model, respectively. The model is applied to the Catalan coast (NW Mediterranean). The outcomes denote spatial patterns that coincide with the state of knowledge. The proposed methodology is able to provide boundary conditions for wave and near-shore studies, saving computational time and establishing the dependence of the proposed variables. Such synthetic storms reproduce the inter-variable co-dependence of the original data.
Situated along the coast of southern China and facing the South China Sea, Hong Kong has been experiencing a significant rise in sea level by about 2.9 mm year−1 since the 1950s. For a densely populated coastal city prone to storm surge impacts during the passages of tropical cyclones, accentuated by the threat of sea-level rise as a result of global warming and local vertical land displacement, projection of the sea-level change for Hong Kong is essential for local risk assessment and long-term planning of adaptation measures. This study presented the projection of sea-level change in Hong Kong and its adjacent waters under the Representative Concentration Pathway 4.5 and 8.5 (RCP4.5 and RCP8.5) scenarios in the 21st century based on climate projections by models in phase 5 of Coupled Model Intercomparison Project, in combination with contributions from land ice and land water storage determined from published literatures, and local vertical land displacement as estimated by using continuous high-precision GPS observations in Hong Kong. The results show that the sea level in Hong Kong and its adjacent waters is projected to rise by 0.67 (0.50–0.84) m and 0.84 (0.63–1.07) m in 2081–2100 relative to 1986–2005 under RCP4.5 and RCP8.5, respectively, about 0.2 m higher than the global mean values projected by the Fifth Assessment Report of Intergovernmental Panel on Climate Change. The higher projected sea-level rise in Hong Kong and its adjacent waters as compared with the global mean values is primarily due to local vertical land displacement which contributes around 28% and 23% of the projected sea-level rise in 2081–2100 relative to 1986–2005 in the two respective RCP scenarios.
Sea-level rise associated with climate change presents a major challenge to plant diversity and ecosystem service provision in coastal wetlands. In this study, we investigate the effect of sea-level rise on benthos, vegetation, and ecosystem diversity in a tidal wetland in west Wales, the UK. Present relationships between plant communities and environmental variables were investigated through 50 plots at which vegetation (species and coverage), hydrological (surface or groundwater depth, conductivity) and soil (matrix chroma, presence or absence of mottles, organic content, particle size) data were collected. Benthic communities were sampled at intervals along a continuum from saline to freshwater. To ascertain future changes to the wetlands' hydrology, a GIS-based empirical model was developed. Using a LiDAR derived land surface, the relative effect of peat accumulation and rising sea levels were modelled over 200 years to determine how frequently portions of the wetland will be inundated by mean sea level, mean high water spring and mean high water neap conditions. The model takes into account changing extents of peat accumulation as hydrological conditions alter.
Model results show that changes to the wetland hydrology will initially be slow. However, changes in frequency and extent of inundation reach a tipping point 125 to 175 years from 2010 due to the extremely low slope of the wetland. From then onwards, large portions of the wetland become flooded at every flood tide and saltwater intrusion becomes more common. This will result in a reduction in marsh biodiversity with plant communities switching toward less diverse and occasionally monospecific communities that are more salt tolerant.
While the loss of tidal freshwater wetland is in line with global predictions, simulations suggest that in the Teifi marshes the loss will be slow at first, but then rapid. While there will be a decrease in biodiversity, the model indicated that at least for one ecosystem service, carbon storage, there is potential for an increase in the near future.
Sea-level rise (SLR) is one of the most apparent climate change stressors facing human society1. Although it is known that many people at present inhabit areas vulnerable to SLR2, 3, few studies have accounted for ongoing population growth when assessing the potential magnitude of future impacts4. Here we address this issue by coupling a small-area population projection with a SLR vulnerability assessment across all United States coastal counties. We find that a 2100 SLR of 0.9 m places a land area projected to house 4.2 million people at risk of inundation, whereas 1.8 m affects 13.1 million people—approximately three times larger than indicated by current populations. These results suggest that the absence of protective measures could lead to US population movements of a magnitude similar to the twentieth century Great Migration of southern African-Americans5. Furthermore, our population projection approach can be readily adapted to assess other hazards or to model future per capita economic impacts.
Sea level rise (SLR) imposes an increasing flooding hazard on low-lying coastal communities due to higher exposure to high-tide conditions and storm surge. Additional coastal flooding hazard arises due to reduced effectiveness of gravity-based drainage systems to drain rainwater during heavy rain events. Over the past decade, several coastal communities along the US Atlantic coast have experienced an increasing rate of flooding events. In this study, we focus on the increasing flooding hazard in Miami Beach, Florida, which has caused severe property damage and significant disruptions to daily life. We evaluate the flooding frequency and its causes by analyzing tide and rain gauge records, media reports, insurance claims, and photo records from Miami Beach acquired during 1998–2013. Our analysis indicates that significant changes in flooding frequency occurred after 2006, in which rain-induced events increased by 33% and tide-induced events increased by more than 400%. We also analyzed tide gauge records from Southeast Florida and detected a decadal-scale accelerating rates of SLR. The average pre-2006 rate is 3 ± 2 mm/yr, similar to the global long-term rate of SLR, whereas after 2006 the average rate of SLR in Southeast Florida rose to 9 ± 4 mm/yr. Our results suggest that engineering solutions to SLR should rely on regional SLR rate projections and not only on the commonly used global SLR projections.
Human-caused climate change is contributing to global sea level rise and consequently aggravating coastal floods. This analysis removes the assessed human-caused component in global sea level from hourly water level records since 1950 at 27 U.S. tide gauges, creating alternative histories simulating the absence of anthropogenic climate change. Out of 8,726 days when unaltered water level observations exceeded National Weather Service local “nuisance” flood thresholds for minor impacts, 5,809 days (3,517-7,332 days, >90% confidence interval) did not exceed thresholds in the alternative histories. In other words, human-caused global sea level rise effectively tipped the balance, pushing high water events over the threshold, for about two-thirds of the observed flood days. The fraction has increased from less than half in the 1950s, to more than three-quarters within the last decade (2005-2014), as global sea level has continued to rise.
Also within the last decade, at sites along Florida’s Atlantic coast and the Keys, as well as in San Diego (La Jolla), Seattle, and Honolulu, more than 90% of observed flood days would not have occurred if the central estimate for anthropogenic sea level signal were removed. The same applies to more than half the flood days at each of the 25 out of 27 study gauges averaging more than one total nuisance flood day per year since 2005. Overall, gauges averaged 12.2 flood days per year over this period.
In the central estimate, the human-caused increase in global sea level also accounts for more 80% of the increase in nuisance flood days between the period 1955-1984 and the period 1985-2014 – periods across which flood frequency tripled for study gauges collectively. Anthropogenic climate change is not just a problem for the future: through sea level rise, it is driving most coastal flooding in the United States today. There are human fingerprints on thousands of recent floods.
This analysis makes the simplifying assumption that the climate-driven human contribution to sea level across the U.S. is uniform and equal to the global mean contribution, putting aside smaller static-equilibrium and dynamic effects that vary in space and time.