Nature-based Adaptation Research Articles

A GIS-MCDA approach to map environmental suitability of Posidonia oceanica meadows as blue nature-based solutions in the Mediterranean eco-region

The growing environmental risks induced by interacting climate and human-induced pressures threaten the survival and growth of marine coastal ecosystems (MCEs) and the ecosystem services they provide. Nature-based solutions (NBS), consisting of ecosystem-based approaches, have emerged as vital tools for climate adaptation and mitigation facing biodiversity loss and societal challenges. Identifying suitable environmental conditions for implementing Blue-NBS in marine coastal areas is a key priority to drive robust and cost-effective nature-based adaptation pathways. This study developed a suitability model for Blue-NBS, with a specific focus on Posidonia oceanica meadows in the Mediterranean Sea under a baseline scenario. GIS-based Multiple Criteria Decision Analysis (MCDA) was applied for data integration and prioritization of different environmental variables in geomorphological (e.g., depth), water quality (WQ) (e.g., salinity), and climatic (e.g., thermal stress) sub-groups. Suitability classes and scores for each variable were determined using statistical distributions, ensuring a data-driven approach to defining environmental suitability. Variables' weights were derived from the Analytic Hierarchy Process (AHP) based on expert judgment and then combined with scores to generate suitability maps for managing Blue-NBS on seagrasses. Depth was found to be the most dominant environmental variable, with shallow areas (e.g., Northern Adriatic, Gulf of Gabés) showing higher suitability. The southern part of the Mediterranean (e.g., Egypt) reported relatively low scores for both climate and WQ, while the Northern Adriatic had the lowest WQ scores. This study represents the first attempt to evaluate Blue-NBS suitability for seagrass meadows at the eco-regional scale with geomorphologic, WQ, and climatic variables, providing decision support for the selection and allocation of Blue-NBS in different environmental settings. The resulting environmental suitability maps represent a basis for the integration of socio-economic and governance-related indicators into a more complex, multi-tier approach to support NBS mainstreaming.

Community-Based Adaptation to Climate Change: Core Issues and Implications for Practical Implementations

According to current forecasts, global heating is likely to exceed 2.8 °C by the end of this century. This makes substantial adaptation measures necessary to secure a broad basis for livelihood provision and the conservation of biodiversity. While the implementation of top-down and technocratic adaptation efforts predominates, related adaptation shortcomings of a socio-economic and ecological nature are becoming more and more apparent. Community-based adaptation (CBA), with its participatory, inclusive and needs-based bottom-up approach, offers a promising and powerful alternative. This article uses a semi-systematic literature review approach to screen the current literature and identify core issues of CBA. Linking communality, locality, multidimensionality, power imbalances, transformative potential, localisation, the triad of adaptation metrics and nature-based adaptation to corresponding potential actions for practical implementations provides a more holistic conceptualisation and broadens the horizons for further learning, research and improved applications.

Climate change adaptation at the margins. The case of Cairo, Egypt

The duration, frequency and intensity of climate change are increasing. Adaptation to climate change is oftentimes perceived as a local concern. Vulnerable groups at the margins try to find nature-based ways to cope with extreme urban climate change events with diverse direct and indirect adaptive strategies in absence of government interventions. From this study's investigative approach in Cairo, Egypt we draw results preliminary from interviews with locals and observational walks in three vulnerable areas in the same urban zone. Research revealed that adaptation can be political, demanding that locals sometimes make hard choices, especially during the absence of government intervention. Nevertheless, some of the adaptive strategies observed can be promoted as mainstream sustainable nature-based adaptation. The discussion reflects some social and economic dimensions that affect local adaptation synergies. This study hopefully contributes to the understanding of how the capacity of individual homeowners can help mitigate climate change risk through the implementation of their own physical and psychological adaptive strategies. In addition, it bears relevance not only for countries sharing similar climates, economic conditions or similar social norms, but also for general adaptation strategies that might support ecosystem-based or nature-based adaptation or tailor-made scenarios for locally applicable adaptation to climate change.

Children’s Cardiovascular Health in a Changing Climate: Associations of Prenatal Heat Stress and Nature-Based Adaptation Features with Child Blood Pressure

Children’s Cardiovascular Health in a Changing Climate: Associations of Prenatal Heat Stress and Nature-Based Adaptation Features with Child Blood Pressure

Tree contributions to climate change adaptation through reduced cattle heat stress and benefits to milk and beef production.

Cattle heat stress causes billions of dollars' worth of losses to meat and milk production globally, and is projected to become more severe in the future due to climate change. Tree establishment in pastoral livestock systems holds potential to reduce cattle heat stress and thus provide nature-based adaptation. We developed a general model for the impact of trees on cattle heat stress, which can project milk and meat production under future climate scenarios at varying spatial scales. The model incorporates the key microclimate mechanisms influenced by trees, including shade, air temperature, humidity, and wind speed. We conducted sensitivity analyses to demonstrate the relative influence of different mechanisms through which trees can impact cattle heat stress, and how tree impacts are influenced by climatic context globally. Trees hold the greatest potential to reduce cattle heat stress in higher latitudes and altitudes, with minor benefits in the lowland tropics. We projected the future contributions of current trees in mitigating climate change impacts on the dairy and beef herds of Aotearoa-New Zealand (A-NZ) in 2070-2080. Trees were simulated to contribute to A-NZ milk yields by over 491 million liters (lower CI = 112 million liters, upper CI = 850 million liters), and meat yields by over 8316 tonnes (lower CI = 2431 tonnes, upper CI = 13,668 tonnes) annually. The total economic contribution of existing trees in mitigating future cattle heat stress was valued at $US 244 million (lower CI = $US 58 million, upper CI = $US 419 million). Our findings demonstrate the importance of existing trees in pastoral landscapes and suggest that strategic tree establishment can be a valuable adaptation option for reducing cattle heat stress under climate change. Tree establishment in the next few years is critical to provide adaptation capacity and economic benefit in future decades.

Levers for transformative nature-based adaptation initiatives in the Alps

Transformative adaptation is essential to face the unprecedented biodiversity and climate change crises and the resulting loss in Nature’s Contribution to People (NCP). Nature-based Solutions (NbS) can accelerate this transformation of social-ecological systems. Understanding the drivers of the decision-making context that support NbS implementation is crucial to address potential bottlenecks and barriers for such a transformative adaptation. Here, semi-structured interviews were conducted with managers of twenty NbS implemented in the Alps. Their decision-making contexts were investigated using the values-rules-knowledge framework and their transformative characteristics. A clustering analysis revealed three types of NbS characterized by specific groups of levers and barriers. Firstly, Local transformation NbS are self-sufficient initiatives motivated by relational values to nature. They are supported by informal governance and share experiential knowledge to support the adaptive capacity of nature. Secondly, Green deal NbS employ a gradual change in practices and are supported by funding opportunities or regulations to experiment with new approaches fostering instrumental values of nature. Thirdly, Multi-scale co-production NbS benefit larger areas and communities. Their social acceptance rest on extensive participatory processes involving local practitioners and diverse values of nature. This last group is designed to persist even when challenged by the instability of funding opportunities. These findings suggest that in order to accelerate the implementation of transformative NbS, future policies need to: i) foster NbS implementation by local communities facing economic constraints when implementing new NbS-related practices; ii) support transdisciplinary programmes to create an inclusive network around NbS practices; and iii) adapt incentives to enable transformative adaptation through NbS. A macro-regional strategy may have the potential to address these challenges.

Fiscal Decentralization and Nature-Based Adaptation Financing: A New Perspective on Sovereign Bond Yields

Fiscal Decentralization and Nature-Based Adaptation Financing: A New Perspective on Sovereign Bond Yields

Integrating Biophysical and Economic Assessment: Review of Nature-Based Adaptation to Urban Flood Extremes

Over the last decade, the potential of nature-based solutions (NBS) has been recognized to support climate change adaptation, by promoting sustainable urban planning. Nevertheless, a wider uptake of such solutions in urban areas faces different challenges and barriers. A comprehensive mapping of available NBS impact assessment methods could help to accelerate this process. There is, however, a lack of comprehensive systematization of economic analysis. This research aims to provide an overview of NBS impact evaluations by assessing how the scientific literature integrates such economic analysis into urban planning adaptation. A systematic review approach has been used to discuss the role of NBS in climate change adaptation. This review presents two main stages. Firstly, it identifies the biophysical–economic assessment of NBS adaptation measures to reduce urban flood extremes in coastal cities. Secondly, the NBS approaches were categorized based on the biophysical benefits (in terms of flood-risk reduction) related to each specific solution and the subsequent economic evaluation of such implementations. This research review revealed a low-level gap of integration between climate change issues and NBS analysis (i.e., it is commonly used as background condition). Most publications provide NBS biophysical impacts assessment, without combining these results with economic evaluation of the flood damages to finally achieve the avoided cost due to the implementation of such solutions. This work shows the growing interest on further research to develop spatially integrated environmental–economic assessment of NBS implementation, by highlighting the needs and opportunities of a trans-disciplinary approach to support policy-making in the framework of urban climate change adaptation.

Revised global estimates of resilience to sea level rise for tidal marshes

Earth system models are widely used to estimate future changes in wetland extent but do not incorporate surface elevation change (SEC) into predicting wetland's real responses to sea level rise (SLR). A machine learning model (MLM) was used to investigate the impact of multiple drivers on SEC and sediment accretion rate (SAR) in tidal marshes, and an earth system model (i.e. integrated climate and wetland migration model) was developed to predict the response of tidal marshes to SLR. The earth system model incorporates factors influencing SEC found by the MLM. Firstly, global data on SAR and SEC for tidal marshes was synthesised and the MLM was used to examine the drivers for SEC and SAR, including tidal range and frequencies, sediment loadings, precipitation, elevation, latitude, sea ice and/or relative SLR (RSLR). Human disturbance resulted in less sediment accretion and existing conservation activities were inefficient in promoting sediment accretion. Secondly, an integrated climate and wetland migration model was developed to assess the resilience of global tidal marshes responding to future SLR in Matlab by incorporating SEC, RSLR, climatic zones, tidal inundation, elevation and latitude into the model. The model was implemented under representative concentration pathways (RCPs) 2.6, 4.5 and 8.5, as well as nature-based human adaptation scenarios. Under the RCPs and nature-based human adaptation scenarios, tidal marshes will gain 53%-58% of the current global area by 2100 if sufficient sediment loadings and accommodation space allow landward migration. If current accommodation space is maintained, net global areal losses of 23%-30% are possible. Hotspots of future marsh loss are largely in North America, Australia and China. Projections for most SLR scenarios see marsh area peaking in the mid rather than late 21st century. Ecogeomorphic feedbacks affect rates of sediment accumulation but cannot be incorporated into the earth system model. The importance of nature-based adaptation was highlighted in enhancing the resilience of tidal marshes to future SLR.

H2020 projects and EU research needs for nature-based adaptation solutions

This paper investigates the documentation produced by 21 Horizon 2020 (H2020) projects for the use of Nature Based Solutions (NBS) for climate change adaptation (NBaS). Accordingly, an updated state-of-the-art on current knowledge and its limits is presented. Findings are then capitalized on for highlighting research needs. The main objective of this study is to inform future orientations on NBaS research. Accordingly, it can be considered as an effort to complement the 2021 European strategy for climate change adaptation, under which NBaS is listed as one of the three cross-cutting priorities. The obtained results reflect actual outcomes from completed projects, while ongoing projects provided a substantial amount of relevant knowledge. From the exhaustive knowledge-research need inventory, one of the most significant identified gaps was the need for developing further the fundamental scientific basis behind these solutions, as the concept favors its practical nature and places less emphasis on its scientific counterpart.

Nature-based solutions must be realized - not just proclaimed - in face of climatic extremes

Natural hazards resulting from climate change are increasing in frequency and intensity. As this is not a linear trend but rather by singularities and anomalies including a broad spectrum of climatic and weather extremes with high temporal and spatial uncertainty, focused avoidance strategies are difficult to prepare. However, the effects of climate change are mostly addressed with outdated ‘business as usual’ approaches by governments and most stakeholders, which are unfit to tackle the complexity of current challenges. Coping action for natural hazards is mostly undertaken during and after such events compensating damage through payments and restoration. In the future, pro-active nature-based solutions are needed for risk mitigation and avoiding severe damage through enhancing all facets of biodiversity from species richness, structural roughness, to spatial heterogeneity of ecosystems. This will not avoid extreme weather events, but it will reduce the damage of increasingly appearing natural hazards. However, this strategy cannot be implemented all of a sudden. Long-term and spatial concepts are needed. For this purpose, currently missing governance structures based on geographical, geoscientific, ecological, meteorological, and societal expertise should be installed. In recent years, a good scientific and knowledge basis for the required solutions has been developed, which now must translate into action. Here, a series of suggestions is compiled for a broad spectrum of extreme events and societal fields, which is far from being complete but should stimulate critically needed creativity and commitment. Nature-based solutions will not deliver a complete protection and cannot be the only kind of action, but we can no longer rely on post-disaster compensation or on the safety illusion of mere engineering and construction works. The efficiency of biodiversity as an insurance for maintaining ecosystem services is well understood. The implementation of nature-based adaptation, coping, and protection measures is less expensive than traditional end-of-the-pipe constructions. It requires an in-depth understanding of interacting processes and trans-disciplinary cooperation based on a broad acceptance in the public. Investments into these solutions would pay off, not tomorrow, but in the future. It is the best sustainable and feasible approach for disaster prevention.

The application of an environmental performance framework for climate adaptation innovations on two nature-based adaptations

In this paper, we introduce and test a framework to qualitatively assess the environmental impact of climate adaptation innovations with the ambition to facilitate the implementation of these adaptations. The framework was designed to enable continuous environmentally conscious benchmarking based on three environmental performance indicators: sustainable design, environmental impact and ecological impact. It was pilot tested by uninvolved experts and key-persons for two large-scale nature-based flood adaptation innovations in the Netherlands and discussed with environmental assessment professionals. Our findings indicate how the inclusion of our framework helps to identify important knowledge gaps regarding environmental co-benefits and trade-offs, and can be beneficial to both those developing the innovation and the local authorities charged with assessing the suitability of innovations. We conclude by noting how the incorporation of environmental impact assessment from the design stage of adaptations could supplement existing environmental assessment regulations pre-empting concerns rather than reacting to them.

Urban greenspace as a climate change adaptation strategy for subtropical Asian cities: A comparative study across cities in three countries

Interest in nature-based approaches for climate change adaptation in cities is growing. Whilst there is a growing field of scholarship in a European and North America setting, research on the policy and governance of urban greenspace for climate adaptation in subtropical Asia is limited. Given the different development patterns, environmental characteristics and governance arrangements in subtropical cities, plus their comparatively large population and high climate risk, this is a significant knowledge gap. In response, this paper evaluates competences – skill sets, capabilities, and supporting policy and legislation – to enact adaptation through greenspace across different governance contexts; and assesses how international rhetoric on nature-based adaptation becomes localised to subtropical Asian city settings. We conduct interviews with stakeholders, plus review of relevant policy and city-specific research, for three cities with different governance and development contexts: Hanoi (Vietnam); Taipei (Taiwan); and Fukuoka (Japan). Across all three cases, we find that institutional structures and processes for connecting different remits and knowledge systems are a bigger challenge than a lack of appropriate policy or individuals with the required technical knowledge. However, opportunities for civil society participation and consideration of justice issues vary between the cities according to the socio-political context. These findings illustrate the value of individuals and organisations able to work across institutional boundaries in linking greenspace and adaptation agendas for subtropical Asian cities; and the importance of competence in collaboration with developers and civil society so that the rapid development or regeneration seen in subtropical Asian contexts does not tend towards green climate gentrification. More broadly, our findings show that the diverse nature of subtropical Asian cities means the role of greenspace in climate adaptation is likely to be context-specific, and thus that caution must be exercised against uncritically importing best practices from exemplar cases elsewhere.

Planning to adaptation: Informing regional nature-based adaptation to improve coastal resiliency in Santa Monica Bay

Los Angeles County is known for its wide sandy beaches, coastal boardwalks, and beach commerce and tourism. Planning for sea level rise and associated coastal hazards poses unique challenges in highly populated urban communities; in particular, sandy beaches play an important role in buffering the land from sea level rise, coastal storms, and associated flooding. With increasing pressure to prepare for and adapt to sea level rise, boundary organizations such as USC Sea Grant and The Bay Foundation are helping coastal communities build their capacity to respond to changing shorelines by providing and translating best available science, providing planning and technical support, building partnerships, and implementing adaptation strategies. This paper evaluates the process and provides recommendations for translating science to on-the-ground planning and adaptation efforts in coastal communities. Regionally, USC Sea Grant’s AdaptLA initiative works with coastal communities to communicate sea level rise science and provide managers with information and tools to assess vulnerabilities and begin to plan for adaptation. Informed by detailed, scaled-down climate change models and science-based demonstration projects, some AdaptLA participants initiated demonstration adaptation projects such as the Santa Monica Beach Restoration Pilot Project discussed in this paper. The Santa Monica Bay case study highlights a sea level rise adaptation process, from community capacity building to planning nature-based adaptation, using beach restoration. Lessons learned from demonstration projects in the region can inform similar projects and potential scaling up of nature-based adaptation on sandy beaches. Through the collective effort of boundary organizations, coordination with multiple jurisdictions and agencies, and community support, this case study demonstrates a model for implementing naturebased adaptation in urban coastal communities.

Effective design of managed realignment schemes can reduce coastal flood risks

Managed realignment (MR) constitutes a form of nature-based adaptation to coastal hazards, including sea level rise and storm surges. The implementation of MR aims at the (re)creation of intertidal habitats, such as saltmarshes, for mitigating flood and erosion risks and for creating more natural shorelines. However, some evidence suggests that the desired coastal protection function of MR schemes (in terms of high water level (HWL) attenuation) may be limited and it was hypothesized that this was due to the configuration of the remaining seawalls, which we refer to as scheme design. Here we present the results of a hydrodynamic model application, which we used to analyse the effects of scheme design on within-site HWL attenuation by applying six scheme designs that differ in terms of breach characteristics and water storage capacity. In specific, we vary the configuration of the seaward defence line (including the seawall breaches) and the position of the landward dike by modifying the digital elevation model of the site.Our results show that changes in scheme design, particularly storage area and number and width of breaches, had significant effects on the site's HWL attenuation capacity. Decreasing the tidal prism by changing the number and size of breaches, with the site area kept constant, leads to increased modelled HWL attenuation rates. However, average HWL attenuation rates of >10 cm km−1 are only achieved when site size increases. The mean high water depth of each scheme design scenario, calculated by dividing tidal prism by MR area, explains most of the variation in average HWL attenuation between all scenarios. Attention to potential within-site hydrodynamics at the design stage will aid the construction of more effective MR schemes with respect to coastal protection in the future.

Nature-Based Solution along High-Energy Eroding Sandy Coasts: Preliminary Tests on the Reinstatement of Natural Dynamics in Reprofiled Coastal Dunes

This paper describes a large-scale experiment designed to examine if reinstating natural processes in the coastal dune systems of Southwest France can be a relevant nature-based adaptation in chronically eroding sectors and a nature-based solution against coastal hazards, by maintaining the coastal dune ecological corridor. An experiment started in late 2017 on a 4-km-long stretch of coast at Truc Vert, where experimental notches were excavated and intensively monitored in the incipient and established foredunes. Preliminary results indicate that most of the excavated notches did not develop into blowout. Only the larger elongated notches subsequently excavated in the established foredune in 2018 showed evidence of development, acting as an effective conduit for aeolian landward transport into the dunes. All notches were found to have a statistically significant impact on vegetation dynamics downwind, even those that did not develop. The area of bare sand landward and within the elongated notches notably increased implying a loss of vegetation cover during this first stage of development. Observations of a nearby coastal dune system that has been in free evolution over the last 40 years also indicate that, although the dune migrated inland by more than 100 m, it is now mostly made of bare sand. Further work is required to explore if and how dunes maintained as dynamic systems can become an efficient nature-based solution along this eroding coastline.

Financing coastal resilience by combining nature-based risk reduction with insurance

The increasing impacts of climate hazards combined with the loss of coastal habitats require urgent solutions to manage risk. Storm losses continue to grow and much of them are uninsured. These losses represent an increasing burden to individuals, businesses, and can jeopardize national development goals. Pre-hazard mitigation is cost effective, but both the public and private sector struggle to finance up-front investments in it. This article explores a resilience solution that combines risk transfer (e.g., insurance) with risk reduction (e.g., hazard mitigation), which have often been treated as two separate mechanisms for disaster risk management. The combined mechanism could help align environmental and risk management goals and create opportunities for public and private investment in nature-based projects. We assessed this resilience insurance with hypothetical cases for coral reef restoration. Under conservative assumptions, 44% of the initial reef restoration costs would be covered just by insurance premium reductions in the first 5 years, with benefits amounting >6 times the total costs over 25 years. We also test the sensitivity to key factors such as project cost, risk reduction potential, insurance structure, economic exposure and discount rates. The resilience insurance mechanism is applicable to many coastlines and can help finance nature-based adaptation.

Environmental and climate policy integration: Targeted strategies for overcoming barriers to nature-based solutions and climate change adaptation

Nature-based adaptation planning is a challenging endeavor, not least because it requires transdisciplinary approaches to unite different actors' efforts and capacities. However, empirical knowledge on associated governance processes is scarce and fragmented. Against this background, this paper examines the integration of nature-based approaches for climate change adaptation into municipalities’ daily planning practices and associated governance. A city-to-city learning lab was established to systematically analyze selected urban development projects step-by-step, from the initial idea, to comprehensive and detailed planning, procurement, implementation, maintenance and follow-up. The results show the numerous constraints municipal staff face and how they use targeted strategies to overcome them and tap into existing drivers. We identify five, complementary strategies: i) targeted stakeholder collaboration; ii) strategic citizen involvement; iii) outsourcing; iv) the alteration of internal working structures; and v) concealed science–policy integration. Importantly, these strategies reveal an increasing need for relational approaches that, in turn, require individuals to develop the cognitive/emotional capacity to establish trust, communicate inclusively and promote social learning, while at the same time dealing with an increasingly complex and uncertain working environment. We conclude that tapping into the potential of nature-based solutions for climate adaptation governance requires more financial and human resources, and capacity development to support personal development, systematic mainstreaming and, ultimately, more sustainable development.

Future response of global coastal wetlands to sea-level rise.

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.

Comparing the cost effectiveness of nature-based and coastal adaptation: A case study from the Gulf Coast of the United States.

Coastal risks are increasing from both development and climate change. Interest is growing in the protective role that coastal nature-based measures (or green infrastructure), such as reefs and wetlands, can play in adapting to these risks. However, a lack of quantitative information on their relative costs and benefits is one principal factor limiting their use more broadly. Here, we apply a quantitative risk assessment framework to assess coastal flood risk (from climate change and economic exposure growth) across the United States Gulf of Mexico coast to compare the cost effectiveness of different adaptation measures. These include nature-based (e.g. oyster reef restoration), structural or grey (e.g., seawalls) and policy measures (e.g. home elevation). We first find that coastal development will be a critical driver of risk, particularly for major disasters, but climate change will cause more recurrent losses through changes in storms and relative sea level rise. By 2030, flooding will cost $134–176.6 billion (for different economic growth scenarios), but as the effects of climate change, land subsidence and concentration of assets in the coastal zone increase, annualized risk will more than double by 2050 with respect to 2030. However, from the portfolio we studied, the set of cost-effective adaptation measures (with benefit to cost ratios above 1) could prevent up to $57–101 billion in losses, which represents 42.8–57.2% of the total risk. Nature-based adaptation options could avert more than $50 billion of these costs, and do so cost effectively with average benefit to cost ratios above 3.5. Wetland and oyster reef restoration are found to be particularly cost-effective. This study demonstrates that the cost effectiveness of nature-based, grey and policy measures can be compared quantitatively with one another, and that the cost effectiveness of adaptation becomes more attractive as climate change and coastal development intensifies in the future. It also shows that investments in nature-based adaptation could meet multiple objectives for environmental restoration, adaptation and flood risk reduction.