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Global coastal flood exposure (population and assets) has been growing since the beginning of the industrial age and is likely to continue to grow through 21st century. Three main drivers are responsible: (1) climate-related mean sea-level change, (2) vertical land movement contributing to relative sea-level rise, and (3) socio-economic development. This paper attributes growing coastal exposure and flood risk from 1860 to 2100 to these three drivers. For historic flood exposure (1860 to 2005) we find that the roughly six-fold increase in population exposure and 53-fold increase in asset exposure are almost completely explained by socio-economic development (>97% for population and >99% for assets). For future exposure (2005 to 2100), assuming a middle-of-the-road regionalized socio-economic scenario (SSP2) without coastal migration and sea-level rise according to RCP2.6 and RCP6.0, climate-change induced sea-level rise will become the most important driver for the growth in population exposure, while growth in asset exposure will still be mainly determined by socio-economic development.

The management of coastal flood risk is adapting to meet the challenges and increased risks posed by population change as well as by climate change, especially sea level rise. Protection is being targeted to areas where the benefits are highest, while elsewhere there is a shift towards more localized “living with floods” and “resilience” approaches. Such decentralized approaches to flood risk management (FRM) require a diverse range of stakeholder groups to be engaged as “flood risk citizens”. Engagement of households in FRM is central to this process. Despite significant research on stakeholder engagement in coastal and flood risk management, there is less focus on the nature of responsibility in coastal adaptation. There is no framework by which to assess the different types of responsibility in hazard management and adaptation, and little research on the implications of expecting these responsibilities of stakeholder groups. In this paper, we identify five types of responsibility that are embedded throughout the disaster risk reduction cycle of managing coastal flooding. We build this “typology of responsibility” on existing work on the evolution of stakeholder engagement and stakeholder responsibility relationships in risk management processes, and a dataset of institutional stakeholder interviews and households surveys conducted across three case studies in England, the United Kingdom, in 2018 and 2019. We analyze the interviews using thematic analysis to explore institutional stakeholder perceptions of responsibility in coastal FRM, and analyze the household survey through descriptive and inferential statistics. By developing the first disaster risk reduction focused typology of responsibility for coastal flooding, we provide researchers and decision-makers with a tool to guide their planning and allocation of responsibilities in risk management for floods and other climate-driven hazards.

The Ganges-Brahmaputra-Meghna (GBM) delta is one of the world's largest deltas. It is currently experiencing high rates of relative sea-level rise of about 5 mm/year, reflecting anthropogenic climate change and land subsidence. This is expected to accelerate further through the 21st Century, so there are concerns that the GBM delta will be progressively submerged. In this context, a core question is: can sedimentation on the delta surface maintain its elevation relative to sea level? This research seeks to answer this question by applying a two-dimensional flow and morphological model which is capable of handling dynamic interactions between the river and floodplain systems and simulating floodplain sedimentation under different flow-sediment regimes and anthropogenic interventions. We find that across a range of flood frequencies and adaptation scenarios (including the natural polder-free state), the retained volume of sediment varies between 22% and 50% of the corresponding sediment input. This translates to average rates of sedimentation on the delta surface of 5.5 mm/yr to 7.5 mm/yr. Hence, under present conditions, sedimentation associated with quasi-natural conditions can exceed current rates of relative sea-level rise and potentially create new land mass. These findings highlight that encouraging quasi-natural conditions through the widespread application of active sediment management measures has the potential to promote more sustainable outcomes for the GBM delta. Practical measures to promote include tidal river management, and appropriate combinations of cross-dams, bandal-like structures, and dredging.

Coastal areas are highly diverse, ecologically rich, regions of key socio-economic activity, and are particularly sensitive to sea- level change. Over most of the 20th century, global mean sea level has risen mainly due to warming and subsequent expansion of the upper ocean layers and the melting of glaciers and ice caps. Over the last three decades, increased mass loss of the Greenland and Antarctic ice sheets has also started to contribute significantly to contemporary sea-level rise. The future mass loss of these ice sheets, which combined represent a sea-level rise potential of ~65 m, constitutes the main source of uncertainty in long-term (centennial to millennial) sea-level rise projections. Improved knowledge of the magnitude and rate of future sea-level change is therefore of utmost importance. Moreover, sea level does not change uniformly across the globe, and can differ greatly at both regional and local scales. The most appropriate and feasible sea level mitigation and adaptation measures in coastal regions strongly depend on local land use and associated risk aversion. Here, we advocate that addressing the problem of future sea-level rise and its impacts requires (i) bringing together a transdisciplinary scientific community, from climate and cryospheric scientists to coastal impact specialists, and (ii) interacting closely and iteratively with users and local stakeholders to co-design and co-build coastal climate services, including addressing the high-end risks. Following these principles, as also adopted in the EU project “Projecting sea-level rise: from projections to local implications” (PROTECT), we encourage the formation of research consortia that cover the entire knowledge chain. In this way global sea-level science can be linked to effective coastal climate services at the scale of risk and adaptation

Climate change is and will continue altering the world's coasts, which are the most densely populated and economically active areas on earth and home for highly valuable ecosystems. While there is considerable relevant research, in the authors' experience this problem remains challenging for coastal engineering. This paper reviews important challenges in this respect and identifies three key actions to address them: (a) refocusing traditional practice towards more climate-aware approaches; (b) developing more comprehensive risk frameworks that include the multi-dimensionality and non-stationarity of their components and consideration of uncertainty; and (c) building bridges between risk assessment and adaptation theory and practice. We conclude that the way forward includes numerous activities including increased observations; the attribution of coastal impacts to their drivers; enhanced climate projections and their integration into impact models; more impact assessments at the local scale; dynamic projections of spatially-distributed exposure and vulnerability; and the exploration of inherently adaptive options. Given the complexity of the possible solutions, more practical guidance is required.

Sea-level rise threatens low-lying areas around the world's coasts with increased coastal flooding during storms. One response to this challenge is to build or upgrade coastal flood defenses. This report examines the potential investment costs of such an adaptation strategy applied globally over the 21st century for sea-level rise scenarios consistent with three Representative Concentration Pathways and 3 Shared Socioeconomic Pathways. For all the protection models considered, much less than half of the world's coast is protected. The total defense costs are significantly higher than earlier estimates, amounting to as much as US$18.3 trillion. With cost-benefit analysis, there are large uncertainties and empirical observations of protection standards are limited. Hence, the estimates should be considered as indicative, and this remains an important topic for future research. Further, building defenses is not a one-off capital investment. Over the 21st century, the cost of a comprehensive protection strategy is dominated by maintenance costs in all the cases considered in this report. This indicates that in addition to capital investment, the development of appropriate institutions and governance mechanisms to deliver maintenance, as well as the necessary funding streams, are essential for such a protection-based adaptation strategy to be effective.

Methods used in "Stabilisation of global temperature at 1.5°C and 2.0°C: Implications for coastal areas"

Coastal flooding caused by extreme sea levels can produce devastating and wide-ranging consequences. The ‘SurgeWatch’ v1.0 database systematically documents and assesses the consequences of historical coastal flood events around the UK. The original database was inevitably biased due to the inconsistent spatial and temporal coverage of sea-level observations utilised. Therefore, we present an improved version integrating a variety of ‘soft’ data such as journal papers, newspapers, weather reports, and social media. SurgeWatch2.0 identifies 329 coastal flooding events from 1915 to 2016, a more than fivefold increase compared to the 59 events in v1.0. Moreover, each flood event is now ranked using a multi-level categorisation based on inundation, transport disruption, costs, and fatalities: from 1 (Nuisance) to 6 (Disaster). For the 53 most severe events ranked Category 3 and above, an accompanying event description based upon the Source-Pathway-Receptor-Consequence framework was produced. Thus, SurgeWatch v2.0 provides the most comprehensive and coherent historical record of UK coastal flooding. It is designed to be a resource for research, planning, management and education.

Understanding the dynamics of salt movement in the soil is a prerequisite for devising 23 appropriate management strategies for land productivity of coastal regions, especially low lying 24 delta regions which support many millions of farmers around the world. In this research, we 25 develop a novel holistic approach to simulate soil salinization comprising an emulator-based soil 26 salt and water balance calculated at daily time steps. The method is demonstrated for the 27 agriculture areas of Coastal Bangladesh. This shows that we can reproduce the dynamics of soil 28 salinity under multiple land uses, including rice crops, combined shrimp and rice farming, as 29 well as non-rice crops. The model also reproduced well the observed spatial soil salinity for the 30 year 2009. Using this approach, we have projected the soil salinity for three different climate 31 ensembles, including relative sea-level rise for the period 2041-2050. The results indicate an 32 increase in soil salinity in 21-44% of the simulated area. This can potentially cause significant 33 crop yield reductions, especially for vegetables and local rice varieties. The modelling approach 34 will enable planners and land use managers to investigate future trajectories of salinity impacts 35 on crop production, considering expected changes in relative sea level, groundwater pumping 36 and water quality in the rivers and estuary, and management responses to augment freshwater 37 supplies.

Coastal and shoreline management increasingly needs to consider morphological change occurring at decadal to centennial timescales, especially that related to climate change and sea-level rise. This requires the development of morphological models operating at a mesoscale, defined by time and length scales of the order 101 to 102 years and 101 to 102 km. So-called ‘reduced complexity’ models that represent critical processes at scales not much smaller than the primary scale of interest, and are regulated by capturing the critical feedbacks that govern landform behaviour, are proving effective as a means of exploring emergent coastal behaviour at a landscape scale. Such models tend to be computationally efficient and are thus easily applied within a probabilistic framework. At the same time, reductionist models, built upon a more detailed description of hydrodynamic and sediment transport processes, are capable of application at increasingly broad spatial and temporal scales. More qualitative modelling approaches are also emerging that can guide the development and deployment of quantitative models, and these can be supplemented by varied data-driven modelling approaches that can achieve new explanatory insights from observational datasets. Such disparate approaches have hitherto been pursued largely in isolation by mutually exclusive modelling communities. Brought together, they have the potential to facilitate a step change in our ability to simulate the evolution of coastal morphology at scales that are most relevant to managing erosion and flood risk. Here, we advocate and outline a new integrated modelling framework that deploys coupled mesoscale reduced complexity models, reductionist coastal area models, data-driven approaches, and qualitative conceptual models. Integration of these heterogeneous approaches gives rise to model compositions that can potentially resolve decadal- to centennial-scale behaviour of diverse coupled open coast, estuary and inner shelf settings. This vision is illustrated through an idealised composition of models for a ~ 70 km stretch of the Suffolk coast, eastern England. A key advantage of model linking is that it allows a wide range of real-world situations to be simulated from a small set of model components. However, this process involves more than just the development of software that allows for flexible model coupling. The compatibility of radically different modelling assumptions remains to be carefully assessed and testing as well as evaluating uncertainties of models in composition are areas that require further attention.

Coastal and shoreline management increasingly needs to consider morphological change occurring at decadal to centennial timescales, especially that related to climate change and sea-level rise. This requires the development of morphological models operating at a mesoscale, defined by time and length scales of the order 101 to 102years and 101 to 102km. So-called ‘reduced complexity’ models that represent critical processes at scales not much smaller than the primary scale of interest, and are regulated by capturing the critical feedbacks that govern landform behaviour, are proving effective as a means of exploring emergent coastal behaviour at a landscape scale. Such models tend to be computationally efficient and are thus easily applied within a probabilistic framework. At the same time, reductionist models, built upon a more detailed description of hydrodynamic and sediment transport processes, are capable of application at increasingly broad spatial and temporal scales. More qualitative modelling approaches are also emerging that can guide the development and deployment of quantitative models, and these can be supplemented by varied data-driven modelling approaches that can achieve new explanatory insights from observational datasets. Such disparate approaches have hitherto been pursued largely in isolation by mutually exclusive modelling communities. Brought together, they have the potential to facilitate a step change in our ability to simulate the evolution of coastal morphology at scales that are most relevant to managing erosion and flood risk. Here, we advocate and outline a new integrated modelling framework that deploys coupled mesoscale reduced complexity models, reductionist coastal area models, data-driven approaches, and qualitative conceptual models. Integration of these heterogeneous approaches gives rise to model compositions that can potentially resolve decadal- to centennial-scale behaviour of diverse coupled open coast, estuary and inner shelf settings. This vision is illustrated through an idealised composition of models for a ~70km stretch of the Suffolk coast, eastern England. A key advantage of model linking is that it allows a wide range of real-world situations to be simulated from a small set of model components. However, this process involves more than just the development of software that allows for flexible model coupling. The compatibility of radically different modelling assumptions remains to be carefully assessed and testing as well as evaluating uncertainties of models in composition are areas that require further attention.

Whilst understanding and predicting the effects of coastal change are primarily modelling problems, it is essential that we have appropriate conceptual frameworks for (1) the formalisation of existing knowledge; (2) the formulation of relevant scientific questions and management issues; (3) the implementation and deployment of predictive models; and (4) meaningful engagement involvement of stakeholders. Important progress continues to be made on the modelling front, but our conceptual frameworks have not evolved at a similar pace. Accordingly, this paper presents a new approach that re-engages with formal systems analysis and provides a mesoscale geomorphological context within which the coastal management challenges of the 21st century can be more effectively addressed. Coastal and Estuarine System Mapping (CESM) is founded on an ontology of landforms and human interventions that is partly inspired by the coastal tract concept and its temporal hierarchy of sediment sharing systems, but places greater emphasis on a hierarchy of spatial scales. This extends from coastal regions, through landform complexes, to landforms, the morphological adjustment of which is constrained by diverse forms of human intervention. Crucially, CESM integrates open coastal environments with estuaries and relevant portions of the inner shelf that have previously been treated separately.In contrast to the simple nesting of littoral cells that has hitherto framed shoreline management planning, CESM charts a complex web of interactions, of which a sub-set of mass transfer pathways defines the sediment budget, and a multitude of human interventions constrains natural landform behaviour. Conducted within a geospatial framework, CESM constitutes a form of knowledge formalisation in which disparate sources of information (published research, imagery, mapping, raw data etc.) are generalised into usable knowledge. The resulting system maps provide a framework for the development and application of predictive models and a repository for the outputs they generate (not least, flux estimates for the major sediment system pathways). They also permit comparative analyses of the relative abundance of landforms and the multi-scale interactions between them. Finally, they articulate scientific understanding of the structure and function of complex geomorphological systems in a way that is transparent and accessible to diverse stakeholder audiences. As our models of mesoscale landform evolution increase in sophistication, CESM provides a platform for a more participatory approach to their application to coastal and estuarine management.

Coastal flood assessments often require the analysis of a complex system of flood sources, pathways and receptors. This can be challenging for traditional numerical modelling approaches. In this paper we use a Bayesian networks approach to assess coastal floodplains as networks of inter-linked elements. A Bayesian network (Bn) model is built to describe flood pathways and estimate flood extents for different extreme events. The network of the Bn model is constructed from a quasi-2D Source – Pathway – Receptor (SPR) systems diagram. The Bn model is applied in Teignmouth in the UK, a coastal floodplain of typical complexity. It identifies two key flood pathways and assesses their sensitivity to changes in sea levels, beach widths and coastal defences. The advantages, utility and limitations of the Teignmouth Bn model are discussed. The process of 2D SPR and Bn model construction helps identify gaps in floodplain understanding and description. The Bn model quantifies inundation probabilities and facilitates the rapid identification of critical pathways and elements, before committing resources to further detailed analysis. The approach is transferable and can be readily applied in local-scale coastal floodplains to obtain a systems-level understanding and inform numerical modelling assumptions.

Deltas represent one of the most densely populated areas in the world. This is especially true for the coastal zone of Bangladesh where more than a thousand people live in each square kilometre of land. Livelihoods, food security and poverty in Bangladesh are strongly dependent on natural resources affected by several factors including climate variability and change, upstream river flow modifications, commercial fish catches in the Bay of Bengal, and engineering interventions such as polderisation. The scarcity of fresh water, saline water intrusion and natural disasters (e.g. river flooding, cyclones and storm surges) have negative impact on drinking water availability and crop irrigation potential; thus severely affect land use and livelihood opportunities of the coastal population. Hydro-environmental changes can be especially detrimental for the well-being of the poorest households that are highly dependent on natural resources. The ESPA Deltas project aims to holistically examine the interaction between the coupled bio-physical environment and the livelihoods of these poor populations in coastal Bangladesh. Here we describe a new integrated model that allows the long-term analysis of the possible changes in this system by linking projected changes in physical processes (e.g. river flows, nutrients), with productivity (e.g. fish, rice), social processes (e.g. access, property rights, migration) and governance/management (e.g. fisheries, agriculture, water and land use management). This integrated approach is designed to provide Bangladeshi policy makers with science-based evidence of possible development trajectories within the coastal delta plain over timescales up to 50 years, including the likely robustness of different governance options on natural resource conservation and poverty levels. This presentation describes the model framework and aims to illustrate the cause-effect relationship in-between changes of the hydro-environment and the livelihoods of the coastal population of Bangladesh. Thus, it adds the human dimension to a civil engineering modelling approach

Shore and shoreline evolution both due to natural and human-induced causes or factors can be variable over a wide range of different temporal and/or spatial scales. Our capability to understand and especially predict this variability is still limited. This can lead to misinterpretation of coastal change information, which hampers informed decision making and the subsequent design and implementation of (soft) engineering interventions. Collecting and describing example observations of shore and shoreline variability is one way to support and improve such human intervention. This paper describes causes and factors for the variability and the resulting possible evolutions of wave-dominated shores and shorelines, which are illustrated by a number of case studies. The new element of this work is that the variability is described in terms of a range of different time and space scales, which helps to structure such analysis. However, it is difficult to generalise the results for arbitrary situations, especially on decadal time scales. Scientific and engineering improvements require more quantitative insight into the physical mechanisms behind the free and forced shore behaviour responsible for the variability.

International audience; For many climate change impacts such as drought and heat waves, global and national frameworks for climate services are providing ever more critical support to adaptation activities. Coastal zones are especially in need of climate services for adaptation, as they are increasingly threatened by sea level rise and its impacts, such as submergence, flooding, shoreline erosion, salinization and wetland change. In this paper, we examine how annual to multi-decadal sea level projections can be used within coastal climate services (CCS). To this end, we review the current state-of-the art of coastal climate services in the US, Australia and France, and identify lessons learned. More broadly, we also review current barriers in the development of CCS, and identify research and development efforts for overcoming barriers and facilitating their continued growth. The latter includes: (1) research in the field of sea level, coastal and adaptation science and (2) cross-cutting research in the area of user interactions, decision making, propagation of uncertainties and overall service architecture design. We suggest that standard approaches are required to translate relative sea level information into the forms required to inform the wide range of relevant decisions across coastal management, including coastal adaptation.

Discussions were undertaken between Hampshire County Council, the Environment Agency and the University of Southampton, School of Civil Engineering and the Environment (Centre for Environmental Sciences). These established a need to investigate the viability of using dredge spoil for saltmarsh restoration and mudflat creation in the Solent (central southern UK).A literature review of current natural and anthropogenic threats to saltmarsh longevity in the UK and worldwide was undertaken. This also considered the potential impact of dredging activities and considered the potential value of keeping sediments within the geomorphological systems. The value of saltmarsh as a habitat, sediment sink, source of nutrients and provider of natural coastal protection was considered. The status of Solent salt marshes, particularly in relation to their conservation value, their source of sediment and wave erosion trends was identified. Both passive and active methods of saltmarsh restoration tried in the UK and worldwide were considered. In particular the use of dredge spoil and methods for its placement and retention were investigated.An overview of legislation in relation to Environmental Impact Assessment and Appropriate Assessment and planning issues was given. Furthermore the matter of trace elements and pollutants potentially associated with dredge spoil, and as a result its suitability for restoration works, was also considered. This was complemented by comment form the main regulatory agencies (the Environment Agency and Natural England) who kindly gave their opinion on procedures and processes that may lead to a Solent saltmarsh restoration trial.This background material was then considered in relation to nine saltmarshes, owned by Hampshire County Council, where restoration may be viable. This was coupled with a further eleven sites identified through the Solent Dynamic Coast Project (SDCP) where use of dredge spoil may be feasible to convert mudflat to saltmarsh. A tool was developed which utilised recommended physical conditions, coupled with conservation designations and socio-economic considerations. GIS analysis showed erosion trends, sediment amounts required, marsh slope and height. In addition analysis considered sediment amounts required to restore marsh/convert mudflat and identified marsh erosion trends (useful to identify sites naturally accreting). A Multi Criteria Analysis (MCA) “traffic light” system combined the above factors and highlighted marshes/mudflats which appear most suitable for restoration.For saltmarsh restoration, based on the MCA of the Hampshire County Council sites, results indicate that Gutner Point, Keyhaven and Calshot show a positive balance of criteria for trial dredge spoil recharge. For mudflat recharge the MCA analysis indicated that West Northney, Farlington and Pagham South show the most positive balance of criteria. Of these three sites West Northney would require the least sediment to be introduced to the system. The availability of dredge spoil for restoration projects was considered with regard to regularity of dredging, possible contaminant concentrations (against EA Action Levels).It is recommended that site visits and consideration of local knowledge be employed to indicate the most suitable restoration method of those identified in section three. Furthermore it is highly recommended that a robust experiment design and program of trials through research should be used to monitor changes in accretion or erosion.Whilst not exhaustively considered, the likely issues associated with a potential Environmental Impact Assessment were highlighted to inform regulators and decisions makers of potential processes necessary before restoration trials and full restoration, could be undertaken.Finally at all times through any proposed restoration trial in the Solent System, it is strongly recommended that close liaison with stakeholders and interested parties is undertaken to ensure all concerns are addressed. The University recommends trials in the region not least to offset historic marsh loss, however these must be undertaken with the precautionary principle in mind.

Results of the physical impacts and adaptation cost assessment of sea-level rise for the European Union are presented for the A2 and B2 SRES socio-economic storylines and for a range of plausible sea-level rise scenarios, using data from the ECHAM4 and HADCM3 Global Climate Models (GCMs) models. In addition, to better understand the sensitivity of the results to the magnitude of sea-level rise, the full IPCC (2001) range of sea level rise predictions and scenarios of no climate change have also been modelled. These results are all derived using the global Dynamic Interactive Vulnerability Assessment (DIVA) tool for assessing regional to global coastal impacts and adaptation. Both the physical and economic impacts of sea-level rise increase with time for both the A2 and B2 storylines, especially under scenarios of high sea-level rise. Without adaptation, significant impacts and therefore damages are apparent. Significant populations are threatened with displacement by flooding and coastal erosion. An exploratory adaptation analysis using standard protection measures of dike construction and beach nourishment, where benefit-cost analysis suggests this is the optimum response, reduces these impacts significantly. While adaptation in Europe is likely to be much more diverse than these two smple options, these results demonstrate the significant benefits of protection, and more generally suggest that widespread adaptation to sustain human coastal activities would be prudent. Moreover, under these protection assumptions, coastal ecosystems are significantly reduced in area, especially under the high sea-level rise scenario and climate change raises significant challenges for wider coastal management in Europe, even if human uses in the coastal zone are protected., JRC.DG.J.2-The economics of climate change, energy and transport

Long-term (>10 years) prediction of morphological behaviour in the coastal zone in response to both direct human interference and projected climatic change is an increasingly important issue in coastal management. recognition of the possible impacts increases, so does the need for more comprehensive model-based better assess long term impacts and plan precautionary interventions. Such models need to be integrated both the morphological subsystem and the ecological subsystem, and their interactions in the coastal By explicitly considering the "need for integration between different disciplines", this paper briefly describes approaches to modelling long-term dynamics of coastal morphology, particularly the modelling of coastal the typical situation: limited data and limited process knowledge, and further complicated by the variability coastal space cover and coastal space use. It is argued that progress in long-term modelling of coastal will be further stimulated by adopting a conceptual framework which can embrace all the data, information, and experience concerning the coastal system of interest, whatever form they have. The objective can by using a top-down modelling conceptual approach which helps to formalise knowledge and experience the coastal area and integrate all the available data, information and models, including qualitative Qualitative modelling, which defines tendencies of evolution, offers an important tool for this goal. proach lends itself to being structured into a model-based Decision Support System (DSS), coupled with Information System (GIS) technology which represent the state-of-the-art of decision support tools mental field.

At scales larger than those where processes are well understood (:2: years), it is difficult to set up traditional process­based models. However, there is a growing demand for predictions of shoreline behaviour at these longer timescales, particularly for beach nourishment. Therefore, we are developing a framework based on parametric (behaviour-oriented) modelling which may be applied to areas where limited observations are available. With the present paper we examine the application of our concepts to a real world case, viz. the beach response at Delray Beach, Florida, to nourishment over a 20 year period. The problems of dealing with profile data are considered. The simple diffusion-based model we utilize cannot reproduce non-uniform behaviour. However if beach volume above a reference contour is considered, the model works well and predicts the erosive losses between renourishments quite effectively. Further improvements and application of the model is considered.

A possible approach for the development of simple predictive methods of shoreface profile evolution is described. We hereby introduce the model concept and describe its applicability on the base of diffusion-type formulations over time scales from seasons, to years and decades.

As geomorphologists embrace ever more sophisticated theoretical frameworks that shift from simple notions of evolution towards single steady equilibria to recognise the possibility of multiple response pathways and outcomes, morphodynamic modellers are facing the problem of how to keep track of an ever-greater number of system feedbacks. Within coastal geomorphology, capturing these feedbacks is critically important, especially as the focus of activity shifts from reductionist models founded on sediment transport fundamentals to more synthesist ones intended to resolve emergent behaviours at decadal to centennial scales. This paper addresses the challenge of mapping the feedback structure of processes controlling geomorphic system behaviour with reference to illustrative applications of Causal Loop Analysis at two study cases: (1) the erosion–accretion behaviour of graded (mixed) sediment beds, and (2) the local alongshore sediment fluxes of sand-rich shorelines. These case study examples are chosen on account of their central role in the quantitative modelling of geomorphological futures and as they illustrate different types of causation. Causal loop diagrams, a form of directed graph, are used to distil the feedback structure to reveal, in advance of more quantitative modelling, multi-response pathways and multiple outcomes. In the case of graded sediment bed, up to three different outcomes (no response, and two disequilibrium states) can be derived from a simple qualitative stability analysis. For the sand-rich local shoreline behaviour case, two fundamentally different responses of the shoreline (diffusive and anti-diffusive), triggered by small changes of the shoreline cross-shore position, can be inferred purely through analysis of the causal pathways. Explicit depiction of feedback-structure diagrams is beneficial when developing numerical models to explore coastal morphological futures. By explicitly mapping the feedbacks included and neglected within a model, the modeller can readily assess if critical feedback loops are included.

The response of coastal wetlands to sea-level rise during the twenty-first century remains uncertain. Global-scale projections suggest that between 20 and 90 per cent (for low and high sea-level rise scenarios, respectively) of the present-day coastal wetland area will be lost, which will in turn result in the loss of biodiversity and highly valued ecosystem services1-3. These projections do not necessarily take into account all essential geomorphological4-7 and socio-economic system feedbacks8. Here we present an integrated global modelling approach that considers both the ability of coastal wetlands to build up vertically by sediment accretion, and the accommodation space, namely, the vertical and lateral space available for fine sediments to accumulate and be colonized by wetland vegetation. We use this approach to assess global-scale changes in coastal wetland area in response to global sea-level rise and anthropogenic coastal occupation during the twenty-first century. On the basis of our simulations, we find that, globally, rather than losses, wetland gains of up to 60 per cent of the current area are possible, if more than 37 per cent (our upper estimate for current accommodation space) of coastal wetlands have sufficient accommodation space, and sediment supply remains at present levels. In contrast to previous studies1-3, we project that until 2100, the loss of global coastal wetland area will range between 0 and 30 per cent, assuming no further accommodation space in addition to current levels. Our simulations suggest that the resilience of global wetlands is primarily driven by the availability of accommodation space, which is strongly influenced by the building of anthropogenic infrastructure in the coastal zone and such infrastructure is expected to change over the twenty-first century. Rather than being an inevitable consequence of global sea-level rise, our findings indicate that large-scale loss of coastal wetlands might be avoidable, if sufficient additional accommodation space can be created through careful nature-based adaptation solutions to coastal management.

The ability to model morphological changes on complex, multi-landform, coasts during decadal to centennial time scales is essential for sustainable coastal management world-wide. One approach involves coupling of landform-specific 15 simulation models (e.g. cliffs, beaches, dunes, estuaries, etc.) that have been independently developed. An alternative, novel, approach explored in this paper is to capture the essential characteristics of the landform-specific models using a common spatial representation within an appropriate software framework. This avoid the problems that result from the model-coupling approach due to between-model differences in the conceptualisations of geometries, volumes and locations of sediment. In the proposed framework, the Coastal Modelling Environment (CoastalME), change in coastal morphology is 20 represented by means of dynamically linked raster and geometrical objects. A grid of raster cells provides the data structure for representing quasi-3D spatial heterogeneity and sediment conservation. Other geometrical objects (lines, areas and volumes) that are consistent with, and derived from, the raster structure represent a library of coastal elements (e.g. shoreline, beach profiles and estuary volumes) as required by different landform-specific models. As a proof-of-concept, we illustrate the capabilities of an initial version of CoastalME by integrating a cliff-beach model and two wave propagation 25 approaches. We verify that CoastalME can reproduce behaviours of the component landform-specific models. Additionally, the integration of these component models within the CoastalME framework reveals behaviours that emerge from the interaction of landforms, which have not previously been captured, such as the influence of the regional bathymetry on the local alongshore sediment transport gradient, the effect on coastal change on an undefended coastal segment and on sediment bypassing of coastal structures.

Deltas are dynamic and the relationships between ecosystem services, livelihoods and well-being within them are multi-scalar and often non-linear. Social mechanisms of access and management vary between different bundles of ecosystem services: a social-ecological system approach therefore identifies the trade-offs and interactions which occur across diverse temporal and spatial scales and communities. Although Bangladesh is moving towards a more urbanised future, access to ecosystem services continues to be critical to the well-being of populations in rural areas. However, rights to those services are available to a diminishing few. Current winners and losers from development processes are persistent, and ecosystem services are unlikely to lift the rural poor out of poverty without a complete restructuring of social and economic relations in rural areas.

Social survey and geographical data, stratified by social-ecological systems, are used to analyse multiple measures of poverty, in-depth information on rural livelihoods and coping strategies for populations in the delta region. The resultant dataset provides extensive information on the ways in which households use ecosystem services to generate well-being. Analysis of the data shows that any reliance on provisioning ecosystem services for farming, aquaculture, fisheries or forest products increases the likelihood of households being above the poverty line. However, high levels of ecosystem service use are associated with high levels of well-being only in those with significant land assets and associated social capital. The data also provide a quantitative baseline understanding that is fundamental to the integrated analysis.

A flexible meta-model, the Delta Dynamic Integrated Emulator Model (ΔDIEM), is developed to capture the socio-biophysical system of coastal Bangladesh as simply and efficiently as possible. Operating at the local scale, calculations occur efficiently using a variety of methods, including linear statistical emulators, which capture the behaviour of more complex models, internal process-based models and statistical associations. All components are tightly coupled, tested and validated, and their behaviour is explored with sensitivity tests. Using input data, the integrated model approximates the spatial and temporal change in ecosystem services and a number of livelihood, well-being, poverty and health indicators of archetypal households. Through the use of climate, socio-economic and governance scenarios plausible trajectories and futures of coastal Bangladesh can be explored.

The magnitude and extent of fluvial, tidal and storm surge flooding in coastal Bangladesh are quantified using hydrodynamic numerical models under a series of climate and sea-level rise scenarios to 2100. Fluvial floods occur from July to October and are confined to the northern part of the coastal region. Tidal floods occur in the southern part of the coastal region along the banks of the estuaries and only last a few hours. The flood extents for both types of flood are influenced by sea-level rise and increased upstream river flows. Flooding associated with cyclone landfall and resulting storm surge also increases in extent, with a nearly four times increase by the end of the century in extreme cases, reinforcing the need for a long-term adaptation strategy.

Census and spatial data are used to analyse geographical variations in poverty and identify the key socio-economic and environmental drivers of poverty. Results show a strong clustering of poverty within the study area with multivariate analysis indicating a significant association with environmental predictors. However, whilst increasing intensity of salinity intrusion is significantly associated with poverty, neither large shrimp nor freshwater prawn farms impact on poverty. The strong association identified between salinity intrusion and poverty could be attributed to loss of arable land, reduced agricultural productivity and income, food insecurity, rural unemployment, social unrest, conflicts and forced migration. This analysis provides important inputs to the integrated analysis of coastal Bangladesh and the delta.

Bangladesh is identified as an impact hotspot for sea-level rise in multiple studies. However, a range of other factors must be considered including catchment management, socio-economic development and governance quality, as well as delta plain biophysical processes. Taking an integrated assessment approach highlights that to 2050 future changes are more sensitive to human choice/policy intervention than climate change, ecosystem services diminish as a proportion of the economy with time, continuing historic trends and significant poverty persists for some households. Hence under favourable policy decisions, development could transform Bangladesh by 2050 making it less vulnerable to longer-term climate change and subsidence. Beyond 2050, the threats of climate change are much larger, requiring strategic adaptation responses and policy changes that must be initiated now.

Bangladesh is a highly flood prone country, reflecting the strongly seasonal regional climate and monsoon river flows of the Ganges, Brahmaputra and Meghna Rivers, its low-lying nature and its position at the north of the Bay of Bengal. Flooding can be classified as either fluvial, tidal, fluvial-tidal or storm surge, each of which create different flood extents and associated damages. Cyclones and associated storm surges can breach embankments threatening life and livelihoods on the coast, while extreme fluvial events can cause extensive flooding of up to a quarter of the national land area. Existing management interventions, including flood warnings, cyclone shelters, and coastal embankments, mitigate flood inundation and its consequences. However, they can affect the hydro- and morphodynamics in the area influencing future flood events.

Human health and well-being is related to the provision of nutrition and food diversity for each socio-ecological system within the study area. Analysis of data from the household survey indicates that under-five malnutrition is higher than the national average within all socio-ecological systems, while adult malnutrition is slightly lower than the national average. Food diversity, particularly calorific and protein intake associated with fish and home-grown food production and consumption, is shown to be beneficial in reducing malnutrition. Although table salt is the highest contributor in daily consumption of sodium, salinity levels of domestic water sources show a correlation with hypertension, irrespective of age and gender, which is higher than the national average. These salinity levels are likely to increase over the twenty-first century.

Deltas are distinct in terms of the concentration of freshwater, nutrients and especially sediment inputs to a small concentrated area of the coastal zone, creating conditions ideal for fertile ecosystems, dense population and high economic activity. Ecosystem services within these areas can provide services significant in the maintenance of well-being for both rural and urban populations. There are significant feedbacks between environmental processes and social dynamics that drive the economic and well-being outcomes for current and future populations. This chapter reviews ecosystem services in deltas and summarises the state of knowledge in this field on how to manage delta ecosystems for the benefit of resident populations and wider society.

Land cover and land use (LCLU) analysis is a central determinant of the current and future relationship between people and local ecosystem services. It provides the spatial basis for the integrated analysis of the study area. Historical change (1989–2010) is identified using classification techniques based on available satellite imagery supported by other data. Nine categories of LULC are identified; water, Bagda (brackish shrimp farming), Galda (freshwater prawn farming), agriculture (non-waterlogged), agriculture (waterlogged), wetlands and mudflats, mangrove, rural settlements and major urban areas. The analysis shows an increase in aquaculture (mainly replacing rice fields), with agriculture becoming more intermixed with settlements. Future LULC scenarios are determined based on stakeholder narratives.

Coastal Bangladesh has experienced social and economic progress over the last 30 years. Rising average income, literacy levels and health outcomes have occurred, often by developing local ecosystem services such as agriculture and fisheries. At the same time, other ecosystem services such as water availability and quality and land stability have deteriorated. Environment-income analysis suggests that the point at which economic wealth feeds into effective environmental protection has not yet been reached for water resources. The study area is characterised by widespread non-stationary dynamics and slowly changing variables, declining resilience, and a growing probability of major system changes in the near future. This suggests that national policies need to address such potential changes to enable sustainable pathways for delta development and management.

Scenario development for integrated analysis focuses on adopting an interdisciplinary approach covering key elements of the biophysical environment as well as changes in livelihoods, education, economics and governance both locally and internationally. Most importantly, the development of these scenarios generates a dialogue across institutions, stakeholders and sectors, with the use of common data and agreement on shared qualitative and quantitative futures. The scenarios adopted combine three alternative future climates and three socio-economic development pathways. Quantification of these issues included estimation based on published data, expert knowledge and stakeholder engagement, particularly where data are most uncertain or unknown. This chapter demonstrates this approach for coastal Bangladesh.