1,721,019 research outputs found
Sustainability of complex social-ecological systems: methods, tools, and approaches
Full text linkNo abstract available
Benefits of climate change mitigation for reducing the impacts of sea-level rise in G-20 countries
No full textThis paper assesses the potential benefits of climate change mitigation in reducing the impacts of sea-level rise over the 21st century in G-20 countries (excluding the European Union as a whole), using the Dynamic Interactive Vulnerability Assessment model. Impacts of the expected number of people flooded annually and wetland losses were assessed. To assess the benefits of mitigation, it was assumed that defences were not upgraded during the study. Globally, with a sea-level rise of 0.68m by the 2080s (with respect to 1980-1999), representing a potential future with limited climate change mitigation, and with the SRES A1 socio-economic scenario, 123 million additional people could be flooded annually and 39% of present global wetland stock could be lost. For a 0.19m rise in sea-level, associated with a substantial reduction in emissions, the number of people flooded could reduce to 13 million per year, with 21% of global wetland stock loss, unless new wetlands emerge. Collectively, non-Annex 1 G-20 countries experience a disproportionate higher number of people flooded in their nations compared with the proportion of population flooded globally. The greatest wetland losses for G-20 countries are projected for Australia, Indonesia and the USA. Thus, G-20 nations with the highest emissions or gross domestic product, frequently do not experience the greatest impacts, despite some of these nations being potentially more able to pay for adaptation. <br/
Non-linear interaction modulates global extreme sea levels, coastal flood exposure, and impacts
Full text linkWe introduce a novel approach to statistically assess the non-linear interaction of tide and non-tidal residual in order to quantify its contribution to extreme sea levels and hence its role in modulating coastal protection levels, globally. We demonstrate that extreme sea levels are up to 30% (or 70 cm) higher if non-linear interactions are not accounted for (e.g., by independently adding astronomical and non-astronomical components, as is often done in impact case studies). These overestimates are similar to recent sea-level rise projections to 2100 at some locations. Furthermore, we further find evidence for changes in this non-linear interaction over time, which has the potential for counteracting the increasing flood risk associated with sea-level rise and tidal and/or meteorological changes alone. Finally, we show how accounting for non-linearity in coastal impact assessment modulates coastal exposure, reducing recent estimates of global coastal flood costs by ~16%, and population affected by ~8%
Global estimates of the impact of a collapse of the West Antarctic ice sheet: an application of FUND
Full text linkThe threat of an abrupt and extreme rise in sea level is widely discussed in the media, but little understood in practise, especially the likely impacts of such a rise including a potential adaptation response. This paper explores for the first time the global impacts of extreme sea-level rise, triggered by a hypothetical collapse of the West Antarctic Ice Sheet (WAIS). As the potential contributions remain uncertain, a wide range of scenarios are explored: WAIS contributions to sea-level rise of between 0.5 and 5 m/century. Together with other business-as-usual sea-level contributions, in the worst case this gives an approximately 6-m rise of global-mean sea level from 2030 to 2130. Global exposure to extreme sea-level rise is significant: it is estimated that roughly 400 million people (or about 8% of global population) are threatened by a 5-m rise in sea level, just based on 1995 data. The coastal module within the Climate Framework for Uncertainty, Negotiation and Distribution (FUND) model is tuned with global data on coastal zone characteristics concerning population, land areas and land use, and then used for impact analysis under the extreme sea-level rise scenarios. The model considers the interaction of (dry)land loss, wetland loss, protection costs and human displacement, assuming perfect adaptation based on cost-benefit analysis. Unlike earlier analyses, response costs are represented in a non-linear manner, including a sensitivity analysis based on response costs. It is found that much of the world’s coast would be abandoned given these extreme scenarios, although according to the global model, significant lengths of the world’s coast are worth defending even in the most extreme case. This suggests that actual population displacement would be a small fraction of the potential population displacement, and is consistent with the present distribution of coastal population, which is heavily concentrated in specific areas. Hence, a partial defence can protect most of the world’s coastal population. However, protection costs rise substantially diverting large amounts of investment from other sectors, and large areas of (dry)land and coastal wetlands are still predicted to be lost. Detailed case studies of the WAIS collapse in the Netherlands, Thames Estuary and the Rhone delta suggest greater abandonment than shown by the global model, probably because the model assumes perfect implementation of coastal protection and does not account for negative feedbacks when implementation is imperfect. The significant impacts found in the global model together with the potential for greater impacts as found in the detailed case studies shows that the response to abrupt sea-level rise is worthy of further research
Tidal marsh restoration for flood risk mitigation: The effectiveness of managed realignment at Freiston Shore, Lincolnshire, UK
Full text linkThe ecosystem services delivered by coastal wetlands are among the most valuable onthe planet, including the mitigation of climate related risks by sequestering carbon at rates several orders of magnitudes faster than tropical rainforests as well as the provision of natural coastal protection. Despite their ecological and socio-economic importance, coastal wetlands have been lost on a large scale in the past centuries, mostly due to human induced stress factors. The projected acceleration of Sea-Level Rise (SLR) may exacerbate the vulnerability of wetlands in the coming centuries, particularly in case of limited accommodation space due to the presence of anthropogenic infrastructure.
Increasing flood risk for low lying coasts and the continued reliance on traditional engineered solutions that have become economically and ecologically unsustainable in many locations require the development of new measures to mitigate these risks. In the last decades, Managed Realignment (MR) has been implemented with the aim to provide a cost effective and ecologically sustainable alternative to conventional coastal defence schemes. MR constitutes one of several Nature-Based Solutions (NBS) making use of the natural wave and surge attenuating capacity of coastal wetlands and their ability to build up vertically at rates often higher than historical SLR. MR involves the realignment of river, estuary or coastal defences to (re-)establish tidal exchange, supporting the formation of coastal wetlands such as mudflats and saltmarshes. Yet, an important knowledge gap constitutes lacking evidence on the true protective value of MR, which fosters political and societal opposition, ultimately counteracting large scale coastal restoration efforts.
This thesis tackles the above knowledge gap in a combined approach, including field measurements and hydrodynamic modelling, to study the effectiveness of High Water Level (HWL) attenuation across one of the earliest and, at time of establishment, largest coastal MR schemes of the United Kingdom: Freiston Shore, located in Lincolnshire on the east coast of England. Between August and October 2017, a series of 16 water level loggers was deployed across the MR site and the adjacent natural saltmarsh to measure the reduction of peak water levels during the highest tides of the year. Subsequently, these data were used to calibrate and validate a hydrodynamic model of the study area, which enabled studying the effects of MR scheme design on the site’s HWL attenuation capacity during these tides. In a last step, the model was implemented to investigate HWL attenuation rates inside the MR site under the influence of very high storm surge levels, by additionally identifying MR width thresholds for HWL attenuation in relation to surge height and vegetation cover. The main findings of this thesis are: 1) The MR site of Freiston Shore does not provide effective HWL attenuation under all measured conditions. 2) At the open coast of Freiston Shore, only large and wide MR sites can effectively attenuate very high tides, and the reduction of storm surges with return periods of more than ten years requires MR widths of >1148 m (measured perpendicular to the coastline). 3) Increased vegetation cover and larger MR widths enable the attenuation of even higher surges. 4) Breaching dikes should be preferred over complete dike removal when coastal protection is the target of MR implementation.
Three priority areas for future research are recommended: 1) Generating more in situ data on MR internal water level dynamics and HWL attenuations, particularly under storm surge conditions. 2) Freiston Shore’s HWL attenuation function is particularly effective when tidal exchange is restricted through narrow dike breaches, which could also be achieved by applying sluices or culverts (i.e. Regulated Tidal Exchange (RTE)). However, this should be balanced against reduced sedimentation rates, limited MR drainage and vegetation establishment, and the potential erosion and widening of dike breaches, which may all result from breaches being designed too narrow or RTE. 3) Investigating the effectiveness and applicability of several MR schemes and other NBS to mitigate flood risks on a regional scale
A new global database for assessing the vulnerability of coastal zones to sea-level rise
No full textA new global coastal database has been developed within the context of the DINAS-COAST project. The database covers the world's coasts, excluding Antarctica, and includes information on more than 80 physical, ecological, and socioeconomic parameters of the coastal zone. The database provides the base data for the Dynamic Interactive Vulnerability Assessment modelling tool that the DINAS-COAST project has produced. In order to comply with the requirements of the modelling tool, it is based on a data model in which all information is referenced to more than 12,000 linear coastal segments of variable length. For efficiency of data storage, six other geographic features (administrative units, countries, rivers, tidal basins or estuaries, world heritage sites, and climate grid cells) are used to reference some data, but all are linked to the linear segment structure. This fundamental linear data structure is unique for a global database and represents an efficient solution to the problem of representing and storing coastal data. The database has been specifically designed to support impact and vulnerability analysis to sea-level rise at a range of scales up to global. Due to the structure, consistency, user-friendliness, and wealth of information in the database, it has potential wider application to analysis and modelling of the world's coasts, especially at regional to global scales
A comparison of two global datasets of extreme sea levels and resulting flood exposure
No full textEstimating the current risk of coastal flooding requires adequate information on extreme sea levels. For over a decade, the only global data available was the DINAS-COAST Extreme Sea Levels (DCESL) dataset, which applies a static approximation to estimate extreme sea levels. Recently, a dynamically derived dataset was developed: the Global Tide and Surge Reanalysis (GTSR) dataset. Here, we compare the two datasets. The differences between DCESL and GTSR are generally larger than the confidence intervals of GTSR. Compared to observed extremes, DCESL generally overestimates extremes with a mean bias of 0.6 m. With a mean bias of -0.2 m GTSR generally underestimates extremes, particularly in the tropics. The DIVA model is applied to calculate the present-day flood exposure in terms of the land area and the population below the 1 in 100-year sea levels. Global exposed population and is 28% lower when based on GTSR instead of DCESL. Considering the limited data available at the time, DCESL provides a good estimate of the spatial variation in extremes around the world. However, GTSR allows for an improved assessment of the impacts of coastal floods, including confidence bounds. We further improve the assessment of coastal impacts by correcting for the conflicting vertical datum of sea level extremes and land elevation, which has not been accounted for in previous global assessments. Converting the extreme sea levels to the same vertical reference used for the elevation data is shown to be a critical step resulting in 39-59% higher estimate of population exposure
Water-level attenuation in global-scale assessments of exposure to coastal flooding: a sensitivity analysis
Full text linkThis study explores the uncertainty introduced in global assessments of coastal flood exposure and risk when not accounting for water level attenuation due to land-surface characteristics. We implement a range of plausible water-level attenuation values for characteristic land-cover classes in the flood module of the Dynamic and Integrated Vulnerability Assessment (DIVA) modelling framework and assess the sensitivity of flood exposure and flood risk indicators to differences in attenuation rates. Results show a reduction of up to 44% in area exposure and even larger reductions in population exposure and expected flood damages when considering water level attenuation. The reductions vary by country, reflecting the differences in the physical characteristics of the floodplain as well as in the spatial distribution of people and assets in coastal regions. We find that uncertainties related to not accounting for water attenuation in global assessments of flood risk are of similar magnitude to the uncertainties related to the amount of SLR expected over the 21st century. Despite using simplified assumptions to account for the process of water level attenuation, which depends on numerous factors and their complex interactions, our results strongly suggest that an improved understanding and representation of the temporal and spatial variation of water levels across floodplains is essential for future impact modelling
Mediterranean UNESCO World Heritage at risk from coastal flooding and erosion due to sea-level rise
Full text linkUNESCO World Heritage sites (WHS) located in coastal areas are increasingly at risk from coastal hazards due to sea-level rise. In this study we assess Mediterranean cultural WHS at risk from coastal flooding and erosion under four sea-level rise scenarios until 2100. Based on the analysis of spatially explicit WHS data, we develop an index-based approach that allows for ranking WHS at risk from 15 both coastal hazards. Here we show that of 49 cultural WHS located in low-lying coastal areas of the Mediterranean, 37 are at risk from a 100-year flood and 42 from coastal erosion, already today. Until 2100, flood risk may increase by 50 % and erosion risk by 13 % across the region, with considerably higher increases at individual WHS. Our results provide a first-order assessment of where adaptation is most urgently needed and can support policymakers in steering local-scale research to devise suitable adaptation strategies for each WHS
- …
