Flood Risk Assessment in the Netherlands: A Case Study for Dike Ring South Holland

Large parts of the Netherlands are below sea level. Therefore, it is important to have insight into the possible consequences and risks of flooding. In this article, an analysis of the risks due to flooding of the dike ring area South Holland in the Netherlands is presented. For different flood scenarios the potential number of fatalities is estimated. Results indicate that a flood event in this area can expose large and densely populated areas and result in hundreds to thousands of fatalities. Evacuation of South Holland before a coastal flood will be difficult due to the large amount of time required for evacuation and the limited time available. By combination with available information regarding the probability of occurrence of different flood scenarios, the flood risks have been quantified. The probability of death for a person in South Holland due to flooding, the so‐called individual risk, is small. The probability of a flood disaster with many fatalities, the so‐called societal risk, is relatively large in comparison with the societal risks in other sectors in the Netherlands, such as the chemical sector and aviation. The societal risk of flooding appears to be unacceptable according to some of the existing risk limits that have been proposed in literature. These results indicate the necessity of a further societal discussion on the acceptable level of flood risk in the Netherlands and the need for additional risk reducing measures.     

Insights into Flood Risk Misperceptions of Homeowners in the Dutch River Delta

Flooding is one of the most significant natural disasters worldwide. Nevertheless, voluntary take-up of individual damage reduction measures is low. A potential explanation is that flood risk perceptions of individual homeowners are below objective estimates of flood risk, which may imply that they underestimate the flood risk and the damage that can be avoided by damage reduction measures. The aim of this article is to assess possible flood risk misperceptions of floodplain residents in the Netherlands, and to offer insights into factors that are related with under- or overestimation of perceived flood risk. We analyzed survey data of 1,848 homeowners in the Dutch river delta and examine how perceptions of flood probability and damage relate to objective risk assessments, such as safety standards of dikes, as well as heuristics, including the availability heuristic and the affect heuristic. Results show that many Dutch floodplain inhabitants significantly overestimate the probability, but underestimate the maximum expected water level of a flood. We further observe that many respondents apply the availability heuristic.     

Measures of Societal Risk and Their Potential Use in Civil Aviation

This article seeks to clarify the conceptual foundations of measures of societal risk, to investigate how such measures may be used validly in commonly encountered policy contexts, and to explore the application of these measures in the field of civil aviation. The article begins by examining standard measures of societal and individual risk (SR and IR), with attention given to ethical as well as analytical considerations. A comprehensive technical analysis of SR is provided, encompassing scalar risk measures, barrier functions, and a utility‐based formulation, and clarifications are offered with respect to the treatment of SR in recent publications. The policy context for SR measures is shown to be critically important, and an extension to a hierarchical setting is developed. The prospects for applying SR to civil aviation are then considered, and some technical and conceptual issues are identified. SR appears to be a useful analytical tool in this context, provided that careful attention is given to these issues.     

Assessment of ductile dike behavior as a novel flood risk reduction measure

Dikes are an effective flood risk reduction measure in deltaic areas. Present risk analyses consist often of decoupled calculations of probabilities of dike failure and calculation of consequences of flooding given dike failure. However, the flood defense design determines not only the probability of failure, but influences the consequences of flooding as well. Especially when the dike has a ductile failure and breach growth behavior, due to a structural robust design, the consequences of flooding reduce. In this article, we present a novel assessment of risks and investments, valuing structural robustness of a construction type, represented by its ductile behavior during high loads. Therefore, the consecutive occurrence of initial dike failure mechanisms, failure path development, breach growth, and consequences is modeled integral and time-dependent. The investments consist of the costs to reinforce or reconstruct the flood defense to behave relatively ductile. This integral assessment enables to compare flood impacts of different construction types and different dimensions of designs. We applied it on a case in a riverine area in the Netherlands. The results show that the total societal costs and the individual risks on victims are very dependent on the construction type. The risk profile of a polder protected by a brittle or a ductile dike differs significantly. The brittle sand dike in the case requires larger dimensions than the more ductile dike with a clay core.     

Managing Societal and Institutional Risk in Child Protection

Public sector services have been reshaped by two interacting factors: the growing dominance of risk management and the growing demands for transparency and accountability. For the caring professions, these have provoked radical reform. Using the child protection service as a case study, this article explores the impact of the changes on a service that deals with conflicting risks and has a poorly articulated knowledge base. Drawing on Rothstein et al. 's distinction between societal and institutional risks, it is argued that difficulties in managing societal risks are creating serious institutional risks. The latter are then being prioritized in the way the system operates. The preoccupation with such risks has been translated into concerted efforts to formalize the work of front line practitioners to make it transparent and auditable. Although done, in part, with the good intention of spreading good practice standards, this formalization has gone beyond the evidenced knowledge base to the extent that it is creating a new picture of "good practice" that omits significant dimensions of work and is distinct from measures of children's safety or welfare. Moreover, the process of formalization acts as an impediment to knowledge development in disciplines where such learning is urgently needed.     

Insights into the Societal Risk of Nuclear Power Plant Accidents

The elements of societal risk from a nuclear power plant accident are clearly illustrated by the Fukushima accident: land contamination, long‐term relocation of large numbers of people, loss of productive farm area, loss of industrial production, and significant loss of electric capacity. NUREG‐1150 and other studies have provided compelling evidence that the individual health risk of nuclear power plant accidents is effectively negligible relative to other comparable risks, even for people living in close proximity to a plant. The objective of this study is to compare the societal risk of nuclear power plant accidents to that of other events to which the public is exposed. We have characterized the monetized societal risk in the United States from major societally disruptive events, such as hurricanes, in the form of a complementary cumulative distribution function. These risks are compared with nuclear power plant risks, based on NUREG‐1150 analyses and new MACCS code calculations to account for differences in source terms determined in the more recent SOARCA study. A candidate quantitative societal objective is discussed for potential adoption by the NRC. The results are also interpreted with regard to the acceptability of nuclear power as a major source of future energy supply.     

Determinants of Probability Neglect and Risk Attitudes for Disaster Risk: An Online Experimental Study of Flood Insurance Demand among Homeowners

Little is known about why individuals place either a high or a very low value on mitigating risks of disaster‐type events, like floods. This study uses panel data methods to explore the psychological factors affecting probability neglect of flood risk relevant to the zero end‐point of the probability weighting function in Prospect Theory, and willingness‐to‐pay for flood insurance. In particular, we focus on explanatory variables of anticipatory and anticipated emotions, as well as the threshold of concern. Moreover, results obtained under real and hypothetical incentives are compared in an experiment with high experimental outcomes. Based on our findings, we suggest several policy recommendations to overcome individual decision processes, which may hinder flood protection efforts.     

Flood Risk Management: US Army Corps of Engineers and Layperson Perceptions

Recent severe storm experiences in the U.S. Gulf Coast illustrate the importance of an integrated approach to flood preparedness planning that harmonizes stakeholder and agency efforts. Risk management decisions that are informed by and address decision maker and stakeholder risk perceptions and behavior are essential for effective risk management policy. A literature review and two expert models/mental models studies were undertaken to identify areas of importance in the flood risk management process for layperson, non‐USACE‐expert, and two USACE‐expert groups. In characterizing and mapping stakeholder beliefs about risks in the literature onto current risk management practice, recommendations for accommodating and changing stakeholder perceptions of flood risks and their management are identified. Needs of the U.S. Army Corps of Engineers (USACE) flood preparedness and response program are discussed in the context of flood risk mental models.     

Risk Perception and Technological Development at a Societal Level

This article tests the hypothesis that the exposure to the threat to societies posed by the introduction of new technologies is associated with a normalization of risk perception. Data collected in 2000 by the International Social Survey Programme (ISSP) on environmental issues were used to explore this hypothesis. Representative samples from 25 countries were employed to assess the national levels of perceived threat to the environment associated with a series of technologies and activities. These values were correlated with economic indicators (mainly from the World Bank) of the diffusion of each of the technologies or activities in each country. Results indicate a negative association of risk perception with the level of technological prevalence (societal normalization effect) and a positive association with the rate of growth of the technology (societal sensitivity effect). These results indicate that the most acute levels of perceived environmental risk are found in those countries where the level of technological prevalence is low but where there has recently been substantial technological development. Environmental awareness is a mediator of the relationship between risk perception and the indices of technological diffusion. This result means that: (1) societal normalization of risk is not a direct consequence of prevalence of the technology, but is driven by awareness of technological development and that (2) societal sensitivity to risk is associated with lower levels of environmental awareness.     

Three Conceptions of Quantified Societal Risk

In several European countries efforts are undertaken, in particular with regard to fixed industrial installations and transport of dangerous substances, to quantify the "societal risk" (SR) of accidents that may cause more than one victim at a time. This article explores the nature of such efforts. SR-models are essentially ways to structure the distribution of potential social costs of decisions about hazardous activities (e.g., costs of risk reduction, of land use forgone). First, the various ways to describe SR quantitatively, and to set limits to SR will be presented in short. Next, using a scheme developed by Fischhoff and colleagues, the various approaches will be placed in broad categories of reaching acceptable risk decisions: bootstrapping, formal analysis, and professional judgment. Each of the three categories offers a particular appreciation of the risks as 'external costs'. This has important political implications. In the discussion it is argued that local SR-limits, by the very nature of SR, should be set in a way that creates consistency with any potential supra-local interests involved. Second, particular attention is paid to the validity of claims that SR-limits should reflect a strong risk aversion.     

Risk Analysis and Risk Management: An Historical Perspective

This paper reviews the history of risk analysis and risk management, giving special emphasis to the neglected period prior to the 20th century. The overall objective of the paper is to: (1) dampen the prevailing tendency to view present-day concerns about risk in an ahistorical context; (2) shed light on the intellectual antecedents of current thinking about risk; (3) clarify how contemporary ideas about risk analysis and societal risk management differ significantly from the past; and (4) provide a basis for anticipating future directions in risk analysis and management.     

Reflections on Risk Perception and Policy1,2

This paper looks critically at the emergence and present status of risk analysis with the aim of assessing its usefulness for policy decisions on risk regulation and the acceptability of risk-bearing innovations. The authors adopt a personal narrative to illustrate their own involvement in risk research and to comment on empirical trends that have resulted in the current fashion for risk workshops. The second part of the paper confronts specific issues in risk research. These are not new problems-indeed several of the questions asked have been taken directly from a list used to structure a recent risk seminar; but the stand taken here is rather less conciliatory than is usual when these issues are discussed. The pessimistic message of this paper is that risk research, especially in the area of risk perception, is being used as a panacea with which to attempt to remedy what are essentially societal and political matters. Risk research is being used as a tool in a discourse which is not concerned with risks per se, nor with the cognitive processes by which people misperceive the risks of new technologies, but whose hidden agenda is the legitimacy of decision-making institutions and the equitable distribution of hazards and benefits. The authors take a subjectivist view, not just of risk but in general, and query the natural science approach to risk perception, with its assumption that universal dimensions of risk perception can be discovered and used in policy-making and setting regulatory standards. Although it is possible to collect subjective data on the wider meanings that risks and benefits associated with technological innovations have for lay publics, the interpretation and recombination of these data into useful policy guidelines is seen as fraught with technical and, above all, political problems.     

A Probabilistic Model of the Economic Risk to Britain's Railway Network from Bridge Scour During Floods

Scour (localized erosion by water) is an important risk to bridges, and hence many infrastructure networks, around the world. In Britain, scour has caused the failure of railway bridges crossing rivers in more than 50 flood events. These events have been investigated in detail, providing a data set with which we develop and test a model to quantify scour risk. The risk analysis is formulated in terms of a generic, transferrable infrastructure network risk model. For some bridge failures, the severity of the causative flood was recorded or can be reconstructed. These data are combined with the background failure rate, and records of bridges that have not failed, to construct fragility curves that quantify the failure probability conditional on the severity of a flood event. The fragility curves generated are to some extent sensitive to the way in which these data are incorporated into the statistical analysis. The new fragility analysis is tested using flood events simulated from a spatial joint probability model for extreme river flows for all river gauging sites in Britain. The combined models appear robust in comparison with historical observations of the expected number of bridge failures in a flood event. The analysis is used to estimate the probability of single or multiple bridge failures in Britain's rail network. Combined with a model for passenger journey disruption in the event of bridge failure, we calculate a system‐wide estimate for the risk of scour failures in terms of passenger journey disruptions and associated economic costs.     

Asteroid Risk Assessment: A Probabilistic Approach

Following the 2013 Chelyabinsk event, the risks posed by asteroids attracted renewed interest, from both the scientific and policy‐making communities. It reminded the world that impacts from near‐Earth objects (NEOs), while rare, have the potential to cause great damage to cities and populations. Point estimates of the risk (such as mean numbers of casualties) have been proposed, but because of the low‐probability, high‐consequence nature of asteroid impacts, these averages provide limited actionable information. While more work is needed to further refine its input distributions (e.g., NEO diameters), the probabilistic model presented in this article allows a more complete evaluation of the risk of NEO impacts because the results are distributions that cover the range of potential casualties. This model is based on a modularized simulation that uses probabilistic inputs to estimate probabilistic risk metrics, including those of rare asteroid impacts. Illustrative results of this analysis are presented for a period of 100 years. As part of this demonstration, we assess the effectiveness of civil defense measures in mitigating the risk of human casualties. We find that they are likely to be beneficial but not a panacea. We also compute the probability—but not the consequences—of an impact with global effects (“cataclysm”). We conclude that there is a continued need for NEO observation, and for analyses of the feasibility and risk‐reduction effectiveness of space missions designed to deflect or destroy asteroids that threaten the Earth.     

Quantitative Assessment of Building Fire Risk to Life Safety

This article presents a quantitative risk assessment framework for evaluating fire risk to life safety. Fire risk is divided into two parts: probability and corresponding consequence of every fire scenario. The time-dependent event tree technique is used to analyze probable fire scenarios based on the effect of fire protection systems on fire spread and smoke movement. To obtain the variation of occurrence probability with time, Markov chain is combined with a time-dependent event tree for stochastic analysis on the occurrence probability of fire scenarios. To obtain consequences of every fire scenario, some uncertainties are considered in the risk analysis process. When calculating the onset time to untenable conditions, a range of fires are designed based on different fire growth rates, after which uncertainty of onset time to untenable conditions can be characterized by probability distribution. When calculating occupant evacuation time, occupant premovement time is considered as a probability distribution. Consequences of a fire scenario can be evaluated according to probability distribution of evacuation time and onset time of untenable conditions. Then, fire risk to life safety can be evaluated based on occurrence probability and consequences of every fire scenario. To express the risk assessment method in detail, a commercial building is presented as a case study. A discussion compares the assessment result of the case study with fire statistics.     

Risk of Extreme Events Under Nonstationary Conditions

The concept of the return period is widely used in the analysis of the risk of extreme events and in engineering design. For example, a levee can be designed to protect against the 100-year flood, the flood which on average occurs once in 100 years. Use of the return period typically assumes that the probability of occurrence of an extreme event in the current or any future year is the same. However, there is evidence that potential climate change may affect the probabilities of some extreme events such as floods and droughts. In turn, this would affect the level of protection provided by the current infrastructure. For an engineering project, the risk of an extreme event in a future year could greatly exceed the average annual risk over the design life of the project. An equivalent definition of the return period under stationary conditions is the expected waiting time before failure. This paper examines how this definition can be adapted to nonstationary conditions. Designers of flood control projects should be aware that alternative definitions of the return period imply different risk under nonstationary conditions. The statistics of extremes and extreme value distributions are useful to examine extreme event risk. This paper uses a Gumbel Type I distribution to model the probability of failure under nonstationary conditions. The probability of an extreme event under nonstationary conditions depends on the rate of change of the parameters of the underlying distribution.     

Comparative Risk and Policy Analysis in Environmental Health

There is increasing interest in the integration of quantitative risk analysis with benefit-cost and cost-effectiveness methods to evaluate environmental health policy making and perform comparative analyses. However, the combined use of these methods has revealed deficiencies in the available methods, and the lack of useful analytical frameworks currently constrains the utility of comparative risk and policy analyses. A principal issue in integrating risk and economic analysis is the lack of common performance metrics, particularly when conducting comparative analyses of regulations with disparate health endpoints (e.g., cancer and noncancer effects or risk-benefit analysis) and quantitative estimation of cumulative risk, whether from exposure to single agents with multiple health impacts or from exposure to mixtures. We propose a general quantitative framework and examine assumptions required for performing analyses of health risks and policies. We review existing and proposed risk and health-impact metrics for evaluating policies designed to protect public health from environmental exposures, and identify their strengths and weaknesses with respect to their use in a general comparative risk and policy analysis framework. Case studies are presented to demonstrate applications of this framework with risk-benefit and air pollution risk analyses. Through this analysis, we hope to generate discussions regarding the data requirements, analytical approaches, and assumptions required for general models to be used in comparative risk and policy analysis.     

Risk Perception and Risk Talk: The Case of the Fukushima Daiichi Nuclear Radiation Risk

Individuals’ perceptions and their interpersonal communication about a risk event, or risk talk, can play a significant role in the formation of societal responses to the risk event. As they formulate their risk opinions and speak to others, risk information can circulate through their social networks and contribute to the construction of their risk information environment. In the present study, Japanese citizens’ risk perception and risk talk were examined in the context of the Fukushima Daiichi nuclear radiation risk. We hypothesized and found that the risk information environment and risk literacy (i.e., competencies to understand and use risk information) interact to influence their risk perception and risk talk. In particular, risk literacy tends to stabilize people's risk perceptions and their risk communications. Nevertheless, there were some subtle differences between risk perception and communication, suggesting the importance of further examination of interpersonal risk communication and its role in the societal responses to risk events.     

Integrated Direct and Indirect Flood Risk Modeling: Development and Sensitivity Analysis

In this article, we propose an integrated direct and indirect flood risk model for small‐ and large‐scale flood events, allowing for dynamic modeling of total economic losses from a flood event to a full economic recovery. A novel approach is taken that translates direct losses of both capital and labor into production losses using the Cobb‐Douglas production function, aiming at improved consistency in loss accounting. The recovery of the economy is modeled using a hybrid input‐output model and applied to the port region of Rotterdam, using six different flood events (1/10 up to 1/10,000). This procedure allows gaining a better insight regarding the consequences of both high‐ and low‐probability floods. The results show that in terms of expected annual damage, direct losses remain more substantial relative to the indirect losses (approximately 50% larger), but for low‐probability events the indirect losses outweigh the direct losses. Furthermore, we explored parameter uncertainty using a global sensitivity analysis, and varied critical assumptions in the modeling framework related to, among others, flood duration and labor recovery, using a scenario approach. Our findings have two important implications for disaster modelers and practitioners. First, high‐probability events are qualitatively different from low‐probability events in terms of the scale of damages and full recovery period. Second, there are substantial differences in parameter influence between high‐probability and low‐probability flood modeling. These findings suggest that a detailed approach is required when assessing the flood risk for a specific region.     

Simulating Behavioral Influences on Community Flood Risk under Future Climate Scenarios

Flood risk is a function of both climate and human behavior, including individual and societal actions. For this reason, there is a need to incorporate both human and climatic components in models of flood risk. This study simulates behavioral influences on the evolution of community flood risk under different future climate scenarios using an agent-based model (ABM). The objective is to understand better the ways, sometimes unexpected, that human behavior, stochastic floods, and community interventions interact to influence the evolution of flood risk. One historic climate scenario and three future climate scenarios are simulated using a case study location in Fargo, North Dakota. Individual agents can mitigate flood risk via household mitigation or by moving, based on decision rules that consider risk perception and coping perception. The community can mitigate or disseminate information to reduce flood risk. Results show that agent behavior and community action have a significant impact on the evolution of flood risk under different climate scenarios. In all scenarios, individual and community action generally result in a decline in damages over time. In a lower flood risk scenario, the decline is primarily due to agent mitigation, while in a high flood risk scenario, community mitigation and agent relocation are primary drivers of the decline. Adaptive behaviors offset some of the increase in flood risk associated with climate change, and under an extreme climate scenario, our model indicates that many agents relocate.