S.N. Jonkman

An overview of quantitative risk measures for loss of life and economic damage.

A comprehensive overview of methods to quantify and limit risks arising from different sources is still missing in literature. Therefore, a study of risk literature was carried out by the authors. This article summarises about 25 quantitative risk measures. A risk measure is defined as a mathematical function of the probability of an event and the consequences of that event. The article focuses mainly on risk measures for loss of life (individual and societal risk) and economic risk, concentrating on risk measurement experiences in The Netherlands. Other types of consequences and some international practices are also considered. For every risk measure the most important characteristics are given: the mathematical formulation, the field of application and the standard set in this field. Some of the measures have been used in a case study to calculate the flood risks for an area in The Netherlands.

Loss of life caused by the flooding of New Orleans after Hurricane Katrina: analysis of the relationship between flood characteristics and mortality.

In this article a preliminary analysis of the loss of life caused by Hurricane Katrina in the New Orleans metropolitan area is presented. The hurricane caused more than 1,100 fatalities in the state of Louisiana. A preliminary data set that gives information on the recovery locations and individual characteristics for 771 fatalities has been analyzed. One-third of the analyzed fatalities occurred outside the flooded areas or in hospitals and shelters in the flooded area. These fatalities were due to the adverse public health situation that developed after the floods. Two-thirds of the analyzed fatalities were most likely associated with the direct physical impacts of the flood and mostly caused by drowning. The majority of victims were elderly: nearly 60% of fatalities were over 65 years old. Similar to historical flood events, mortality rates were highest in areas near severe breaches and in areas with large water depths. An empirical relationship has been derived between the water depth and mortality and this has been compared with similar mortality functions proposed based on data for other flood events. The overall mortality among the exposed population for this event was approximately 1%, which is similar to findings for historical flood events. Despite the fact that the presented results are preliminary they give important insights into the determinants of loss of life and the relationship between mortality and flood characteristics.

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.

Costs of Adapting Coastal Defences to Sea-Level Rise— New Estimates and Their Implications

ABSTRACT Jonkman, S.N.; Hillen, M.M.; Nicholls, R.J.; Kanning, W., and van Ledden, M., 2013. Costs of adapting coastal defences to sea-level rise—new estimates and their implications. The cost of upgrading and raising coastal defences is an important consideration in societal response to sea-level rise. Currently available unit cost estimates have a limited empirical basis. This article presents new information on the unit costs of adapting coastal defences for three specific case studies in low-lying delta regions: The Netherlands, New Orleans, and Vietnam. Typical measures include dikes, flood walls, storm surge barriers, and nourishment. These unit cost estimates are significantly higher than earlier estimates that are still the main source of costs for global vulnerability assessments. Factors affecting these unit costs include local economic factors (material and labour costs), design choices related to the alignment of the system, and the types of measures for implementation of the system in an urban or rural environment. On the basis of an example for a Dutch sea dike, it is shown that the material quantities and associated costs are expected to rise linearly, in the case of depth-limited wave breaking, for the range of sea-level rise rates that are expected in the coming century. However, other factors, such as increasing costs for implementation of wider coastal defences in an urban environment and future changes in material and labour costs, could contribute to a nonlinear increase of the costs. Further collection and analysis of project information for coastal defence projects in other regions is recommended to strengthen the empirical basis of the cost estimates that are used for regional and global assessments.

The use of individual and societal risk criteria within the Dutch flood safety policy-nationwide estimates of societal risk and policy applications

The Dutch government is in the process of revising its flood safety policy. The current safety standards for flood defenses in the Netherlands are largely based on the outcomes of cost-benefit analyses. Loss of life has not been considered separately in the choice for current standards. This article presents the results of a research project that evaluated the potential roles of two risk metrics, individual and societal risk, to support decision making about new flood safety standards. These risk metrics are already used in the Dutch major hazards policy for the evaluation of risks to the public. Individual risk concerns the annual probability of death of a person. Societal risk concerns the probability of an event with many fatalities. Technical aspects of the use of individual and societal risk metrics in flood risk assessments as well as policy implications are discussed. Preliminary estimates of nationwide levels of societal risk are presented. Societal risk levels appear relatively high in the southwestern part of the country where densely populated dike rings are threatened by a combination of river and coastal floods. It was found that cumulation, the simultaneous flooding of multiple dike rings during a single flood event, has significant impact on the national level of societal risk. Options for the application of the individual and societal risk in the new flood safety policy are presented and discussed.

Evaluation of tunnel safety: towards an economic safety optimum

The aim of this paper is to propose a method for the evaluation of tunnel safety using probabilistic risk assessment. The framework includes three criteria; personal-, societal- and economic risk. The use of personal and societal risk is becoming more and more widespread. There are however, still some difficulties in using the economic risk criterion. As a first step towards economic risk optimisation, the cost effectiveness of addition and removal of safety measures in tunnels is investigated. Finally, the application of the three proposed criteria is further discussed for some tunnelling projects currently underway in the Netherlands.

A general approach for the estimation of loss of life due to natural and technological disasters

Abstract In assessing the safety of engineering systems in the context of quantitative risk analysis one of the most important consequence types concerns the loss of life due to accidents and disasters. In this paper, a general approach for loss of life estimation is proposed which includes three elements: (1) the assessment of physical effects associated with the event; (2) determination of the number of exposed persons (taking into account warning and evacuation); and (3) determination of mortality amongst the population exposed. The typical characteristics of and modelling approaches for these three elements are discussed. This paper focuses on “small probability–large consequences” events within the engineering domain. It is demonstrated how the proposed approach can be applied to various case studies, such as tunnel fires, earthquakes and flood events.

Assessment of flood risk accounting for river system behaviour

Abstract In this paper “river system behaviour” is defined as the complex interaction between river flow and the flooding of flood prone areas. A basic aspect of river system behaviour is that a local dike breach may affect hydraulic loads and hence dike failure probabilities at other locations. Important aspects in river system behaviour are discussed as well as the fact that effects of river system behaviour on flood risk may be both beneficial as well as adverse. This paper presents a conceptual approach to quantify effects of river system behaviour on probabilities of dike breach and flood risk. It was successfully applied to two example river configurations. The results of these examples are discussed. It is concluded that for proper flood risk assessment all relevant failure mechanisms, uncertainties as well as all proposed safety improvement measures are to be jointly taken into account. The conceptual approach enable all this. In the authors’ views, there is a need for developing models that account for effects of river system behaviour on flood risk. Such models can serve as a tool for policy makers in evaluating the effects that (regional) safety improvement measures have on the flood risk in the entire river basin.

Trends in flood losses in Europe over the past 150 years

Adverse consequences of floods change in time and are influenced by both natural and socio-economic trends and interactions. In Europe, previous studies of historical flood losses corrected for demographic and economic growth (‘normalized’) have been limited in temporal and spatial extent, leading to an incomplete representation of trends in losses over time. Here we utilize a gridded reconstruction of flood exposure in 37 European countries and a new database of damaging floods since 1870. Our results indicate that, after correcting for changes in flood exposure, there has been an increase in annually inundated area and number of persons affected since 1870, contrasted by a substantial decrease in flood fatalities. For more recent decades we also found a considerable decline in financial losses per year. We estimate, however, that there is large underreporting of smaller floods beyond most recent years, and show that underreporting has a substantial impact on observed trends.Flooding may cause loss of life and economic damage, therefore temporal changes need assessment. Here, the authors show that since 1870 there has been an increase in area inundated by floods in Europe, but a reduction in fatalities and economic losses, although caution that smaller floods remain underreported.

Integrated risk assessment for the natomas basin (California) analysis of loss of life and emergency management for floods

This article assesses the risk to life for the Natomas Basin, a low-lying, rapidly urbanizing region in the Sacramento-San Joaquin Delta in California. Using an empirical method, the loss of life is determined for a flood (high water), seismic, and sunny-day levee breach scenario. The analysis indicated that more than 1000 fatalities may occur in the flood scenario and that there is a high flood risk compared to similar systems (such as dams and flood-prone areas in the Netherlands). Findings show that risk to life highly depends on evacuation effectiveness. The evacuation and emergency management system (EEM) was further analyzed through interviews with regional emergency managers and training exercise evaluation reports. Using an analytic framework, critical factors that affect EEM performance and reliability were identified. Results indicate a need to assess EEM performance to improve preparedness and reduce the risk to life. Findings from the investigation contribute to more integrated risk analyses of both the technical and management components for engineered systems.