The increasing worldwide trend in disasters, which will be aggravated by global environmental change (including climate change), urges us to implement new approaches to hazard mitigation, as well as exposure and vulnerability reduction. We are, however, faced with hard choices about hazard mitigation: should we continue to build dikes and walls to protect ourselves against floods and coastal hazards – though we have seen the limits of these – or should we consider alternative, ecosystem-based solutions? Ecosystem management is a well-tested solution to sustainable development that is being revisited because of its inherent “win-win” and “no-regrets” appeal to address rising disaster and climate change issues. It is one of the few approaches that can impact all elements of the disaster risk equation – mitigating hazards, reducing exposure, reducing vulnerabilities and increasing the resilience of exposed communities. Yet, the uptake of ecosystem-based approaches for disaster risk reduction (DRR) is slow despite some very good examples of success stories. Reasons for this are multiple: ecosystem management is rarely considered as part of the portfolio of DRR solutions because the environmental and disaster management communities typically work independently from each other; its contribution to DRR is highly undervalued compared to engineered solutions and thus not attributed appropriate budget allocations; finally, there are poor science-policy interactions on ecosystem-based DRR, which have led to unclear and sometimes contradictory scientific information on the role of ecosystems for DRR. The aim of this book is to provide an overview of knowledge and practice in this multi-disciplinary field of ecosystem management and DRR. It contains 17 chapters written by 57 professionals from the science and practice communities around the world, representing state-of-the-art knowledge, practices and perspectives on the topic. It will serve as a basis to encourage and further develop dialogues between scientists, practitioners, policymakers and development planners.
NbS Approach: Disaster Risk Reduction
Ecosystem-based disaster risk reduction
A healthy natural coastal ecosystem can function as one of the components in reducing potential risk of coastal disasters. The impacts of tsunamis, storm surges and coastal erosions can be reduced at a certain limit by the existence of coastal forest and dunes. In Indonesia, tsunami occurs once twice a year in average. It means, tsunami hit quiet frequently even though the return period in a specific location mostly is several tens to hundred years. To reduce potential impacts of tsunamis in coastal area, construction and rehabilitation of coastal forest is one of the main efforts. The existence of a healthy coastal forest not only provides a suitable protection for high frequency but relatively minor to medium scale tsunamis, but also promotes economic activity based on eco-tourism that will ensure the sustainability of the coastal forest maintenance in the later phase. This paper aims to describe milestones of tsunami mitigation by using greenbelt in Indonesia. Conception, tsunami hazards assessment, challenges and lessons learnt in applying tsunami mitigation by using greenbelt are described so the initiative can be replicated in other tsunami prone areas.
The brief look at NBSs from the viewpoint of flood risk management suggests that the relatively new concept seems to be worthwhile for further consideration in both science and practice. Not at least as the need for a close cooperation between various scientific disciplines and multiple sectoral and local stakeholders seems to open up some room for joint innovation.
Shorelines at the interface of marine, estuarine and terrestrial biomes are among the most degraded and threatened habitats in the coastal zone because of their sensitivity to sea level rise, storms and increased human utilization. Previous efforts to protect shorelines have largely involved constructing bulkheads and seawalls which can detrimentally affect nearshore habitats. Recently, efforts have shifted towards ‘‘living shoreline’’ approaches that include biogenic breakwater reefs. Our study experimentally tested the efficacy of breakwater reefs constructed of oyster shell for protecting eroding coastal shorelines and their effect on nearshore fish and shellfish communities. Along two different stretches of eroding shoreline, we created replicated pairs of subtidal breakwater reefs and established unaltered reference areas as controls. At both sites we measured shoreline and bathymetric change and quantified oyster recruitment, fish and mobile macroinvertebrate abundances. Breakwater reef treatments mitigated shoreline retreat by more than 40% at one site, but overall vegetation retreat and erosion rates were high across all treatments and at both sites. Oyster settlement and subsequent survival were observed at both sites, with mean adult densities reaching more than eighty oysters m22 at one site. We found the corridor between intertidal marsh and oyster reef breakwaters supported higher abundances and different communities of fishes than control plots without oyster reef habitat. Among the fishes and mobile invertebrates that appeared to be strongly enhanced were several economically-important species. Blue crabs (Callinectes sapidus) were the most clearly enhanced (+297%) by the presence of breakwater reefs, while red drum (Sciaenops ocellatus) (+108%), spotted seatrout (Cynoscion nebulosus) (+88%) and flounder (Paralichthys sp.) (+79%) also benefited. Although the vertical relief of the breakwater reefs was reduced over the course of our study and this compromised the shoreline protection capacity, the observed habitat value demonstrates ecological justification for future, more robust shoreline protection projects.
Whether or not exacerbated by climate change, flood risks are becoming more frequent in the capital city of Nouakchott in Mauritania. Flooding in Nouakchott is due to a combination of both natural factors and human activities. The extreme fragility of the barrier beach that protects the city from the sea, the accelerated exploitation and inadequate infrastructure built along the coast have made this barrier beach highly vulnerable to wave action, exposing the city to a high risk of flooding. Flooding is further exacerbated by rising groundwater levels in several neighborhoods of the city. Cartographic analysis of flood risk indicated that socio-economic impacts associated with floods could be high. In the case of sea water intrusion, up to 30 % of the city could be potentially submerged. This would directly affect nearly 300,000 people and entail high risks of casualties. Associated economic losses due to flooding could be as high as USD 7 billion (Senhoury, Ame´nagements portuaires et urbanisation accelere´e des coˆtes basses sableuses d’Afrique de l’Ouest dans un contexte de pejoration climatique, cas du littoral de Nouakchott (Mauritanie). Thesis state, University of Dakar, April 29, 2014, 157 pp, 2014). The following measures based on nature-based approaches are recommended to tackle flood risks in Nouakchott: • Restore and consolidate the barrier beach through reforestation of degraded areas; • Put in place an appropriate drainage system for rain and marine waters and a sewage sanitation system; • Optimize a solution to safeguard the harbor of Nouakchott; and • Transform wetlands created by the permanent flooding of low-lying areas in the city into urban protected areas.
Background: Salt marshes lie between many human communities and the coast and have been presumed to protect these communities from coastal hazards by providing important ecosystem services. However, previous characterizations of these ecosystem services have typically been based on a small number of historical studies, and the consistency and extent to which marshes provide these services has not been investigated. Here, we review the current evidence for the specific processes of wave attenuation, shoreline stabilization and floodwater attenuation to determine if and under what conditions salt marshes offer these coastal protection services. Methodology/Principal Findings: We conducted a thorough search and synthesis of the literature with reference to these processes. Seventy-five publications met our selection criteria, and we conducted meta-analyses for publications with sufficient data available for quantitative analysis. We found that combined across all studies (n = 7), salt marsh vegetation had a significant positive effect on wave attenuation as measured by reductions in wave height per unit distance across marsh vegetation. Salt marsh vegetation also had a significant positive effect on shoreline stabilization as measured by accretion, lateral erosion reduction, and marsh surface elevation change (n = 30). Salt marsh characteristics that were positively correlated to both wave attenuation and shoreline stabilization were vegetation density, biomass production, and marsh size. Although we could not find studies quantitatively evaluating floodwater attenuation within salt marshes, there are several studies noting the negative effects of wetland alteration on water quantity regulation within coastal areas.
Conclusions/Significance: Our results show that salt marshes have value for coastal hazard mitigation and climate change adaptation. Because we do not yet fully understand the magnitude of this value, we propose that decision makers employ natural systems to maximize the benefits and ecosystem services provided by salt marshes and exercise caution when making decisions that erode these services.
The benefit-cost-ratio (BCR), used in cost-benefit analysis (CBA), is an indicator that attempts to summarize the overall value for money of a project. Disaster costs continue to rise and the demand has increased to demonstrate the economic benefit of disaster risk reduction (DRR) to policy makers. This study compiles and compares original CBA case studies reporting DRR BCRs, without restrictions as to hazard type, location, scale, or other parameters. Many results were identified supporting the economic effectiveness of DRR, however, key limitations were identified, including a lack of: sensitivity analyses, meta-analyses which critique the literature, consideration of climate change, evaluation of the duration of benefits, broader consideration of the process of vulnerability, and potential disbenefits of DRR measures. The studies demonstrate the importance of context for each BCR result. Recommendations are made regarding minimum criteria to consider when conducting DRR CBAs.
Coastal lowlands and estuaries are subjected to increasing flood risks during storm surges due to global and regional changes. Tidal wetlands are increasingly valued as effective natural buffers for storm surges by dissipating wave energy and providing flood water storage. While previous studies focused on flood wave attenuation within and behind wetlands, this study focuses on the effects of estuarine wetland properties on the attenuation of a storm tide that propagates along the length of an estuary. Wetland properties including elevation, surface area, and location within the estuary were investigated using a numerical model of the Scheldt estuary (Belgium, SW Netherlands). For a spring tide lower wetland elevations result in more attenuation of high water levels along the estuary, while for a higher storm tide higher elevations provide more attenuation compared to lower wetland elevations. For spring and storm tide a larger wetland surface area results in a better attenuation along the estuary up to a threshold wetland size for which larger wetlands do not further contribute to more attenuation. Finally a wetland of the same size and elevation, but located more upstream in the estuary, can store a larger proportion of the local flood volume and therefore has a larger attenuating effect on upstream high water levels. With this paper we aim to contribute towards a better understanding and wider implementation of ecosystem-based adaptation to increasing estuarine flood risks associated with storms.
As ecosystem-based adaptation to global change is gaining ground, strategies to protect coastal and estuarine areas from increasing flood hazards are starting to consist of natural tidal wetland conservation and restoration in addition to conventional coastal defense structures. In this study, the capacity of tidal wetlands to locally attenuate peak water levels during storm tides is analyzed using a two-dimensional hydrodynamic model (TELEMAC-2D) for a 3000 ha intertidal marsh (SW Netherlands). Model results indicate that peak water level reduction largely varies between individual flooding events and between different locations in the marsh. Model scenarios with variable dike positions show that attenuation rates can be minimized by blockage and set up of water levels against dikes or other structures confining the marsh size. This blockage only affects peak water level attenuation across wetlands if the duration of the flood wave is long compared to the marsh size. A minimum marsh width of 6 to 10 km is required to completely avoid blockage effects for the storm tidal cases assessed in this study. If blockage does not affect flood wave propagation, variations in attenuation rates between different locations in the marsh and between tides with varying high water levels can be explained with a single relationship based on the ratio between the water volume on the marsh platform and the total water volume on the platform and in the channels. Attenuation starts to occur when this ratio exceeds 0.2-0.4 and increases from there on up to a maximum of 29 cm/km for a ratio of about 0.85. Furthermore, model scenarios with varying marsh channel depth show that marsh scale attenuation rates increase by up to 4 cm/km if the channel elevation is raised by 0.7 m on average. Conversely, marsh scale attenuation rates decrease by up to 2 cm/km for scenarios in which the channels are lowered by 0.9 m on average. The marsh platform elevation has little effect on the maximum attenuation, but it determines which tides are attenuated. In particular, only overmarsh tides that inundate the platform are attenuated, while undermarsh tides that only flood the marsh channels are not attenuated or even amplified. These findings may assist coastal communities and managers in the optimization of the coastal defense function of tidal wetlands in combination with dikes.
Coastal vegetation has been widely recognized as a natural method to reduce the energy of tsunami waves. However, a vegetation barrier cannot completely stop a tsunami, and its effectiveness depends on the magnitude of the tsunami as well as the structure of the vegetation. For coastal rehabilitation, optimal planning of natural coastal systems, and their maintenance, we need to quantitatively elucidate the capacity of vegetation to reduce the energy of tsunami waves. The limitations of coastal forests in relation to the magnitude of a tsunami and the maintenance of forests as natural disaster buffer zones have to be understood correctly for effective coastal vegetation planning. Demerits of coastal forests have also been revealed: for example, an open gap in a forest (i.e., a road, river, difference in elevation, etc.) can channel and amplify a strong current by forcing it into the gap. Floating debris from broken trees also can damage surrounding buildings and hurt people. However, many studies have revealed that these demerits can be overcome with proper planning and management of mangroves and coastal forests, and that coastal vegetation has a significant potential to mitigate damage in constructed areas and save human lives by acting as buffer zones during extreme natural events. However, mangrove forests have been damaged by anthropogenic activities (i.e., tourism, shrimp farming, and industrial development), making coastal areas increasingly vulnerable to tsunamis and other natural disasters. The effectiveness of vegetation also changes with the age and structure of the forest. This highlights the fact that proper planning and management of vegetation are required to maintain the tsunami buffering function of coastal forests. Although many government and nongovernmental organizations have implemented coastal vegetation projects, many of them have been unsuccessful due to a lack of proper maintenance. A pilot project in Matara City, Sri Lanka, revealed that participation and support from local authorities and communities is essential to make the planting projects successful. An integrated coastal vegetation management system that includes utilization of the materials produced by the forest and a community participation and awareness program are proposed to achieve a sustainable and long-lasting vegetation bioshield.
Building land with a rising sea and a growing coastal population requires strategies that combine conventional engineering with the restoration and maintenance of wetlands and natural delta-building processes. Advances in ecosystem-based engineering may mitigate the risks associated with conventional engineering and rising energy costs. The few existing examples, however, are too recently implemented to fully evaluate their long-term success. More proof-of-concept projects with extensive monitoring are urgently needed in the search for science-based solutions to safeguard delta societies around the world.
The risk of flood disasters is increasing for many coastal societies owing to global and regional changes in climate conditions, sea-level rise, land subsidence and sediment supply. At the same time, in many locations, conventional coastal engineering solutions such as sea walls are increasingly challenged by these changes and their maintenance may become unsustainable. We argue that flood protection by Ecosystem creation and restoration can provide a more sustainable, cost-effective and ecologically sound alternative to conventional coastal engineering and that, in suitable locations, it should be implemented globally and on a large scale.
The risk that tropical storm occurrence may alter as a result of global warming presents coastal managers, particularly in vulnerable areas, with a serious challenge. Many countries are hard-pressed to protect their coastal resources against present-day hazards, let alone any increased threat in the future. Moreover, the threat posed by climate change is uncertain making the increased costs of protection difficult to justify. Here, we examine one management strategy, based on the rehabilitation of the mangrove ecosystem, which may provide a dual, ‘winwin’ benefit in improving the livelihood of local resource users as well as enhancing sea defences. The strategy, therefore, represents a precautionary approach to climate impact mitigation. This paper quantifies the economic benefits of mangrove rehabilitation undertaken, inter alia, to enhance sea defence systems in three coastal Districts of northern Vietnam. The results of the analysis show that mangrove rehabilitation can be desirable from an economic perspective based solely on the direct use benefits by local communities. Such activities have even higher benefit cost ratios with the inclusion of the indirect benefits resulting from the avoided maintenance cost for the sea dike system which the mangrove stands protect from coastal storm surges.
Ecosystems, climate change, and disaster risk reduction are among the cross-cutting issues highlighted in the Rio+20 Conference. In view of the post-2015 development agenda, the chapter discusses the important role of ecosystem-based disaster risk reduction in sustaining ecosystems and building disaster-resilient communities. It describes ecosystem management strategies that link ecosystem protection and disaster risk reduction, elucidates the challenges in advancing the use of ecosystem-based disaster risk reduction and linking it to policy, and identifies opportunities for scaling up.
It is increasingly recognized that uncertainty concerns more than statistical errors and incomplete information. Uncertainty becomes particularly important in decision-making when it influences the ability of the decision-makers to understand or solve a problem. While the literature on uncertainty and the way in which uncertainty in decision-making is conceptualized continue to evolve, the many uncertainties encountered in policy development and projects are still mostly represented as individual and separated issues. In this paper, we explore the relationship between fundamentally different uncertainties – which could be classified as unpredictability, incomplete knowledge or ambiguity – and show that uncertainties are not isolated. Based on two case studies of ecological engineering flood defence projects, we demonstrate that important ambiguities are directly related to unpredictability and incomplete knowledge in cascades of interrelated uncertainties. We argue that conceptualizing uncertainties as cascades provides new opportunities for coping with uncertainty. As the uncertainties throughout the cascade are interrelated, this suggests that coping with a particular uncertainty in the cascade will influence others related to it. Each uncertainty in a cascade is a potential node of intervention or facilitation. Thus, if a particular coping strategy fails or system conditions change, the cascades point at new directions for coping with the uncertainties encountered. Furthermore, the cascades can function as an instrument to bridge the gap between actors from science and policy, as it explicitly shows that uncertainties held relevant in different arenas are actually directly related.
Compared to traditional hard engineering, nature-based flood protection can be more cost effective, use up less raw materials, increase system adaptability and present opportunities to improve ecosystem functioning. However, high flood safety standards cause the need to combine nature-based structures with traditional civil engineered structures. This increases complexity assessing when and how ecological and engineering objectives of such flood protection systems are achieved. This study classifies the degree to which coastal designs are nature based using criteria for ecosystem-based management (EBM). For the engineering criterion the distinction between main and supporting structures is introduced. To evaluate the ecological criterion five design concepts have been introduced, ranging from completely engineered to completely nature-based. The method results in an EBM-ranking of the coast, showing where a particular flood protection design stands on the range between completely engineered (low EBM-rank) and nature-based (high EBM-rank). It thus facilitates comparison of different flood protection systems. The method was the applied on the North-Sea coast of Belgium, the Netherlands, and Germany. The results show that combinations of civil-engineered and nature-based structures are widely applied. However, due to the overall low contribution to flood protection by the nature-based structures, about 85% of the coast is dominated by engineered structures. The majority of these stretches is located in relatively sheltered areas. Improving the flood protection capacity of the nature-based structures in these areas is hard to achieve. Therefore, application of more nature-based design concepts on the main structures is the most promising way to improve the EBM-rank of many flood protection systems.
Low-lying, densely populated coastal areas worldwide are under threat, requiring coastal managers to develop new strategies to cope with land subsidence, sea-level rise and the increasing risk of storm-surge-induced floods. Traditional engineering approaches optimizing for safety are often suboptimal with respect to other functions and are neither resilient nor sustainable. Densely populated deltas in particular need more resilient solutions that are robust, sustainable, adaptable, multifunctional and yet economically feasible. Innovative concepts such as ‘Building with Nature’ provide a basis for coastal protection strategies that are able to follow gradual changes in climate and other environmental conditions, while maintaining flood safety, ecological values and socio-economic functions. This paper presents a conceptual framework for Building with Nature that is used to evaluate coastal protection strategies, based on a case study of the Holland coast in the Netherlands. The added value and the limitations of these strategies are discussed.
There is extensive experience in adaptive management of exposed sandy coastlines through sand nourishment for coastal protection. However, in complex estuarine systems, coastlines are often shortened through damming estuaries to achieve desired safety levels. The Dutch Deltaworks illustrate that this approach disrupts natural sediment fluxes and harms ecosystem health, which negatively affects derived ecosystem services, such as freshwater availability and mussel and oyster farming. This heavily impacts local communities and thus requires additional maintenance and management efforts. Nevertheless, the discussion on coastline shortening keeps surfacing when dealing with complex coastal management issues throughout the world. Although adaptive delta management accompanied by innovative approaches that integrate coastal safety with ecosystem services is gaining popularity, it is not yet common practice to include adaptive pathways, a system-based view and ecosystem knowledge into coastal management projects. Here, we provide a first attempt to integrate ecosystem-based flood risk reduction measures in the standard suite of flood risk management solutions, ranging from structural to non-structural. Additionally, for dealing with the dynamic and more unpredictable nature of ecosystems, we suggest the adaptive delta management approach that consists of flexible measures, measurable targets, monitoring and intervention, as a framework for embedding ecosystem-based alternatives for flood risk mitigation in the daily practice of engineers and coastal planners.
Ecosystem destruction not only incurs large costs for restoration but also increases hydraulic forces on existing flood defence infrastructure. This realisation has made the inclusion of ecosystems and their services into flood defence schemes a rapidly growing field. However, these new solutions require different design, construction and management methods. A close collaboration between engineers, ecologists and experts in public administration is essential for adequate designs. In addition, a mutual understanding of the basic principles of each other’s field of expertise is paramount. This chapter presents some simple approaches for the integration of ecosystem-based measures into coastal engineering projects, which may be of use to experts from a range of fields. Further, it stresses the importance of ecological processes which determine the persistence and health of coastal ecosystems, a point which is rarely emphasised in coastal engineering. The main aim of this chapter is to highlight the role of ecosystem properties for flood defence to stimulate the coastal engineering community in adopting an ecosystem view. In the near future the hope is that greater awareness of ecosystem processes will lead to more sustainable and climate-robust designs. For this, engineers, ecologists and social scientists involved in coastal defence projects need to develop a common language, share the same design concepts and be willing to share the responsibility for these innovative designs.
Cost Benefit Analysis (CBA) is underutilised in assessing Ecosystem- based Disaster Risk Reduction (Eco-DRR) interventions, the protocols used are not always rigourous and the analytical framework is unclear. However, CBAs which follow best practices could be extremely beneficial and helpful to policy makers in establishing priorities for Eco-DRR interventions. A robust and systematic economic analytical approach might be useful, if not necessary, to justify large upfront investments and promote the implementation of this type of risk reduction intervention at an even broader scale. Identifying a common core of best practices for CBA applied to Eco-DRR would also increase comparability between studies, reproducibility of assessments, and facilitate much needed external review. The purpose of this chapter is to (i) outline the fundamental principles and best practices of rigourous cost-benefit analysis (CBA) applied to ecosystem-based adaptation (EbA) and (Eco-DRR) interventions; (ii) review existing studies; and – based on this review of past work – (iii) outline the possible areas of improvement to strengthen future CBAs of Eco-DRR projects.
Vegetated foreshores such as salt marshes, mangrove forests and reed fields can reduce wave loads on coastal dikes due to depth-induced wave breaking and wave attenuation by vegetation. Here we present field measurements of wave propagation over salt marshes during severe storm conditions, a modelling approach to describe the effect of vegetated foreshores on wave loads on the dike, and a probabilistic model to quantify the effect of vegetated foreshores on failure probabilities of the dike due to wave overtopping.
Functioning ecosystems can buffer communities from many negative impacts of a changing climate. Flooding, in particular, is one of the most damaging natural disasters globally and is projected to increase in many regions. However, estimating the value of “green infrastructure” in mitigating downstream floods remains a challenge. We estimate the economic value of flood mitigation by the Otter Creek floodplains and wetlands to Middlebury, VT, for Tropical Storm Irene and nine other floods. We used first principles to simulate hydrographs for scenarios with and without flood mitigation by upstream wetlands and floodplains. We then mapped flood extents for each scenario and calculated monetary damages to inundated structures. Our analysis indicates damage reductions of 84–95% for Tropical Storm Irene and 54–78% averaged across all 10 events. We estimate that the annual value of flood mitigation services provided to Middlebury, VT, exceeds $126,000 and may be as high as $450,000. Economic impacts of this magnitude stress the importance of floodplain and wetland conservation, warrant the consideration of ecosystem services in land use decisions, and make a compelling case for the role of green infrastructure in building resilience to climate change.
Organisations and governments around the globe are developing methodologies to cope with increasing numbers of disasters and climate change as well as implementing risk reducing measures across diverse socio-economic and environmental sectors and scales. What is often overlooked and certainly required for comprehensive planning and programming are better tools and approaches that include ecosystems in the equations. Collectively, these mechanisms can help to enhance societies’ abilities to capture the protective benefits of ecosystems for communities facing disaster and climate risks. As illustrated within this chapter, decision support tools and approaches are clearly improving rapidly. Despite these advancements, factors such as resistance to change, the cautious approach by development agencies, governance structure and overlapping jurisdictions, funding, and limited community engagement remain, in many cases, pre-requisites to successful implementation of ecosystem-based solutions. Herein we provide case studies, lessons learned and recommendations from applications of decision support tools and approaches that advance better risk assessments and implementation of ecosystem-based solutions. The case studies featured in this chapter illustrate opportunities that have been enhanced with cutting edge tools, social media and crowdsourcing, cost/benefit comparisons, and scenario planning mechanisms. Undoubtedly, due to the large areas and extent of exposure to natural hazards, ecosystems will increasingly become a critical part of societies’ overall responses to equitably solve issues of disaster risk reduction and climate change adaptation.
Since the late 1960s it became clear that a more sustainable protection of people and property from the negative impacts of natural hazards will require a more balanced use of structural and non-structural measures, such as land-use planning and ecosystem-based solutions for disaster risk reduction, also called Eco-DRR. The most prominent example of Eco-DRR in mountainous regions are forests that protect people, settlements and infrastructures against gravitational natural hazards such as avalanches, landslides and hazards related to mountain torrents. The goal of this paper is to provide an overview on the influence of forests on risks induced by natural hazards and the associated challenges and uncertainties concerning risk analysis. Approaches from natural hazard risk are presented, along with recent results from forest research, thereby offering new ways to integrate forests into risk analysis. We discuss the potential effects of forests on the three important hazard components of the risk concept, namely the onset probability, the propagation probability and the intensity, and propose a set of guiding principles for integrating forests into quantitative risk assessment (QRA) for natural hazards. Our focus thereby lies on snow avalanches, rockfalls, floods, landslides, and debris flows. This review shows that existing methods and models for assessing forest effects on natural hazards suffice for integrating forests into QRA. However, they are mostly limited to the stand- or slope-scale, and further efforts are therefore needed to upscale these approaches to a regional level, and account for uncertainties related to forest effects and natural dynamics. Such a dynamic, rather than a static assessment of risk will finally allow for planning and implementing intelligent combinations of Eco-DRR and technical protection measures.
Much of the United States’ critical infrastructure is either aging or requires significant repair, leaving U.S. communities and the economy vulnerable. Outdated and dilapidated infrastructure places coastal communities, in particular, at risk from the increasingly frequent and intense coastal storm events and rising sea levels. Therefore, investments in coastal infrastructure are urgently needed to ensure community safety and prosperity; however, these investments should not jeopardize the ecosystems and natural resources that underlie economic wealth and human well-being. Over the past 50 years, efforts have been made to integrate built infrastructure with natural landscape features, often termed “green” infrastructure, in order to sustain and restore valuable ecosystem functions and services. For example, significant advances have been made in implementing green infrastructure approaches for stormwater management, wastewater treatment, and drinking water conservation and delivery. However, the implementation of natural and nature-based infrastructure (NNBI) aimed at flood prevention and coastal erosion protection is lagging. There is an opportunity now, as the U.S. government reacts to the recent, unprecedented flooding and hurricane damage and considers greater infrastructure investments, to incorporate NNBI into coastal infrastructure projects. Doing so will increase resilience and provide critical services to local communities in a cost-effective manner and thereby help to sustain a growing economy.