A commonly used landscape model to simulate wetland change – the Sea Level Affecting Marshes Model (SLAMM) – has rarely been explicitly assessed for its prediction accuracy. Here, we evaluated this model using recently proposed neutral models – including the random constraint match model (RCM) and growing cluster model (GrC), which consider the initial landscape conditions instead of starting with a blank or randomized initial map as traditional neutral models do. Thus, the SLAMM's performance, due to processes accounted for in the model, could be more accurately assessed. RCM allocates change randomly in space, while in the GrC, change allocation is prioritized at the locations with pairs of to-be-increased land type and to-be-reduced land type adjacent to each other. The metrics we applied to evaluate the SLAMM vs. the neutral models accounted for five main components in map comparison: (1) reference change simulated correctly as change (hits), (2) reference persistence simulated correctly as persistence (correct rejections), (3) reference change simulated incorrectly as change to the wrong category (wrong hits), (4) reference change simulated incorrectly as persistence (misses), and (5) reference persistence simulated incorrectly as change (false alarms). These methods improved the way that we currently evaluate land change models, where we either do not compare to a neutral model, or the neutral model does not have the same boundary conditions and constraints as the assessed dynamics models. The results showed that the SLAMM could simulate wetland change more accurately compared to the GrC and RCM at a 10-year time step for the lower Pascagoula River basin, Mississippi, with higher hits and correct rejections, and lower misses and false alarms. The magnitude of simulated changes using the SLAMM was 46% of reference changes. The number of wrong hits for the SLAMM was also lower than those for the neutral models after combining some land or water types into broader categories. After the aggregation, the SLAMM performance improved substantially. How the errors of this relatively short-term simulation propagate into longer-term predictions requires further investigation. This study also showed the importance of implementing elevation data with high vertical accuracy, and conducting local calibration when we apply the SLAMM.
Sea-level Rise, Coastal Flooding, and Storm Events
Conventionally flood mapping typically includes only a static water level (e.g. peak of a storm tide) in coastal flood inundation events. Additional factors become increasingly important when increased water-level thresholds are met during the combination of a storm tide and increased mean sea level. This research incorporates factors such as wave overtopping and river flow in a range of flood inundation scenarios of future sea-level projections for a UK case study of Fleetwood, northwest England. With increasing mean sea level it is shown that wave overtopping and river forcing have an important bearing on the cost of coastal flood events. The method presented converts inundation maps into monetary cost. This research demonstrates that under scenarios of joint extreme surge-wave-river events the cost of flooding can be increased by up to a factor of 8 compared with an increase in extent of up to a factor of 3 relative to “surge alone” event. This is due to different areas being exposed to different flood hazards and areas with common hazard where flood waters combine non-linearly. This shows that relying simply on flood extent and volume can under-predict the actual economic impact felt by a coastal community. Additionally, the scenario inundation depths have been presented as “brick course” maps, which represent a new way of interpreting flood maps. This is primarily aimed at stakeholders to increase levels of engagement within the coastal community.
Currently, risk assessments related to rising sea levels and the adoption of defensive or adaptive measures to counter these sea level increases are underway for densely populated deltas where economic losses might be important, especially in the developed world. However, many underpopulated deltas harbouring high biological and cultural diversity are also at risk but will most likely continue to be ignored as conservation targets. In this study, we explore the potential effects of erosion, inundation and salinisation on one of the world's comparatively underpopulated megadeltas, the Orinoco Delta. With a 1 m sea level rise expected to occur by 2100, several models predict a moderate erosion of the delta's shorelines, migration or loss of mangroves, general inundation of the delta with an accompanying submersion of wetlands, and an increase in the distance to which sea water intrudes into streams, resulting in harm to the freshwater biota and resources. The Warao people are the indigenous inhabitants of the Orinoco Delta and currently are subject to various socioeconomic stressors. Changes due to sea level rise will occur extremely rapidly and cause abrupt shifts in the Warao's traditional environments and resources, resulting in migrations and abandonment of their ancestral territories. However, evidence indicates that deltaic aggradation/accretion processes at the Orinoco delta due to allochthonous sediment input and vegetation growth could be elevating the surface of the land, keeping pace with the local sea level rise. Other underpopulated and large deltas of the world also may risk immeasurable biodiversity and cultural losses and should not be forgotten as important conservation targets.
This study presents estimates of the impact adaptation costs due to damage to coastal and marine structures located along the Mediterranean coast of Israel caused by sea-level rise in the 21st century. The study examines the effects on various types of constructions, including seaports, power plants, marinas, desalination plants, sea walls, detached breakwaters, and bathing beach infrastructures for sea-level rises of 0.5 m and 1 m. To this end, we conduct an analysis of hydrodynamic forces on the structures and an uncertainty analysis of their occurrence. The study find that the impact of wave overtopping of breakwaters can lead to extensive damage to port infrastructure and to the vessels moored inside. Adaptation costs are computed as the corrective measures to be taken to maintain the functionality of the structures.
The impact of mean sea level rise (SLR) on extreme water levels is investigated using a numerical model that covers the entire North Sea, but has its highest spatial resolution in the northern part of the German Bight. A 40-year hindcast covering the period 1970 to 2009 is conducted using observed mean sea level (MSL) changes, tides and atmospheric forcing as boundary conditions. The model reproduces the observed water levels well for this control period. A second 40-year run is then conducted considering the same atmospheric forcing but adding + 0.54 m to the MSL to explore the effects of sea level rise on storm surges in the investigation area. At most locations, the second model run leads to changes in the storm surge water levels that are significantly different from the changes in MSL alone. The largest increases of the order of 15 cm (in addition to the MSL changes) occur in the shallow water areas of the Wadden Sea. These increases in storm surge water levels are caused by nonlinear changes in the tidal constituents which are spatially not coherent. The response of the tidal propagation to SLR is investigated based on the results from a tidal analysis of each individual event. These analyses point to an increase in the M2 amplitude and decrease in the amplitudes of frictional and overtides accompanied by less tidal wave energy dissipation. Attributed effects are changes in phase lags of individual constituents leading to a different tidal modulation, thus additionally increasing tidal water levels. Finally, we estimate how SLR affects return water levels in the northern part of the German Bight, with the result that relevant design water levels increase due to the non-linear relationship between SLR and changes in extremes.
The coastal zones face much higher risks disasters and vulnerability to natural and anthropogenic forcing because of their location in extremely high-energy and rapidly developing environment. We develop and implement an updated set of indicators of coastal vulnerability that characterise relatively low-lying coastal segments with negligible tidal range but affected by substantial storm surges driven by atmospheric factors. The study area is about 90 km long coast of Lithuania in the south-eastern Baltic Sea. The classical methods for building the coastal vulnerability index (CVI) are combined with the outcome analytical hierarchical process (AHP) based approach for incorporating experts' judgements to specify the weights of used criteria. The CVI relies mostly on geological parameters (shoreline change rate, beach width/height, underwater slope, sand bars, and beach sediments) and involves only significant wave height as the representative of direct physical drivers. The selected criteria were integrated into CVI calculation using two options: (I) all criteria contribute equally, (II) each criteria may have a different contribution. Based on the weights and scores derived using AHP vulnerability maps are prepared to highlight areas with very low, low, medium, high and very high vulnerability. CVIw calculation based on option II highlighted 32% of the coast being of very high to high vulnerability, 22% of moderate vulnerability and 41% of low to very low vulnerability. Although these numbers vary to some extent depending on the viewpoint, in general about 10% of the coast in the study area is under very high risk, which calls for urgent planning and protective measures.
Traditional methods for assessing coastal hazards have not typically incorporated a rigorous treatment of uncertainty. Such treatment is necessary to enable risk assessments which are now required by emerging risk based coastal zone management/planning frameworks. While unresolved issues remain, relating to the availability of sufficient data for comprehensive uncertainty assessments, this will hopefully improve in coming decades. Here, we present a modelling framework which integrates geological, engineering and economic approaches for assessing the climate change driven economic risk to coastal developments. The framework incorporates means for combining results from models that focus on the decadal to century time scales at which coasts evolve, and those that focus on the short term and seasonal time scales (storm bite and recovery). This paper demonstrates the functionality of the framework in deriving probabilistic coastal hazard lines and their subsequent use to establish an economically optimal setback line for development at a case study site; the Narrabeen–Collaroy embayment in Sydney, New South Wales.
Today scores of coastal communities are seeing more frequent flooding during high tides. As sea level rises higher over the next 15 to 30 years, tidal flooding is expected to occur more often, cause more disruption, and even render some areas unusable — all within the time frame of a typical home mortgage.
An analysis of 52 tide gauges in communities stretching from Portland, Maine to Freeport, Texas shows that most of these communities will experience a steep increase in the number and severity of tidal flooding events over the coming decades, with significant implications for property, infrastructure, and daily life in affected areas.
Given the substantial and nearly ubiquitous rise in the frequency of floods at these 52 locations, many other communities along the East and Gulf Coasts will need to brace for similar changes.