Current Directions in the Practice of Environmental Risk Assessment

For flood defense inspection, these factors might include the design standard, the physical ... In England and Wales, some two million homes and busin...
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Environ. Sci. Technol. 2002, 36, 530-538

Current Directions in the Practice of Environmental Risk Assessment in the United Kingdom SIMON J. POLLARD,* ROGER YEARSLEY, NICK REYNARD, IAN C. MEADOWCROFT, RAQUEL DUARTE-DAVIDSON, AND SUSAN L. DUERDEN National Centre for Risk Analysis and Options Appraisal, Environment Agency, Kings Meadow House, Kings Meadow Road, Reading, RG1 8DQ, United Kingdom

The manner in which regulators apply environmental risk assessment to their decisions on managing risk is changing. Expectations of risk assessment work are becoming clearer, the social issues agenda is having an impact on risk assessment practice, and there is a trend toward harmonizing approaches to the treatment of environmental risk. For risk analysts, the multiplicity of environmental problems is providing opportunities for the transfer of expertise between the different contexts of applying environmental risk assessment. With the latter as a focus, we summarize recent policy developments in the United Kingdom and illustrate how Government guidance on environmental risk assessment and management is being implemented. We emphasize the need for proportionality in risk analysis, the targeting of regulatory effort to risk, and the explicit treatment of uncertainty. These developments are contributing toward better “risk-informed” environmental decisions in which risk analysis plays an important part alongside other considerations. The forward agenda is likely to see further practical integration between technical risk issues and economic and social concerns, and the positioning of environmental risk assessment within a broader landscape of decision-making tools.

Introduction The use of environmental risk assessment has received growing prominence in the United Kingdom (UK) since the early 1990s, in part, as a response to the explicit requirements of recent environmental legislation. For practitioners, one result has been the emergence of a set of common themes that cut across the technical contexts in which environmental risk assessment is applied, from ecological risk to process plant failure. For example, assessing the risks associated with the performance of radioactive waste repositories, the environmental safety of process plants, the impacts of climate change on water resources, chemical exposures from historically contaminated land, and flood defense schemes involves the treatment of uncertainties. Environmental risk assessment, where applied to these situations, must be able to inform and improve regulatory and business decisions on how best to manage risks from environmental hazards. Arguably, however, the treatment of environmental risk by * Corresponding author phone: +44 (0)1189 535 249; fax +44 (0)1189 535 265; e-mail: simon.pollard@environment-agency. gov.uk. 530 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 4, 2002

nuclear, chemical, and civil engineers, and by climatologists and environmental scientists has developed along parallel lines without an obvious impetus for the transfer of expertise between specialists. This is changing. Government interest in the consistent handling of risk in Europe and the UK is drawing professional communities of experts closer. No more so is this evident than in the field of environmental risk. This “convergence” has been given increased impetus by recent risk episodes in the UK and by legitimate calls for greater participation in environmental decision-making (1-4). Rechard (5) provides an exhaustive review of international developments in environmental risk assessment. Historically, there have been philosophical differences between environmental risk assessment practice in United States (US) and in the UK. In the US, risk assessment developed out of the requirements of food, drug, and pesticide legislation, while in the UK, early drivers were the setting of occupational exposure limits, the safety case requirements of the offshore oil industry, and their subsequent adoption to on-shore process facilities (6). As practice developed, the US approach retained an emphasis on quantified risk estimation, particularly for cancer risk, while the UK, in general, adopted a more cautious approach to quantification, promoting qualitative approaches as a prerequisite. These generalized philosophies are now also converging, driven by a need for targeted, streamlined, and inclusive approaches (7) and a desire to position risk assessment within the range of support tools available to decision-makers (8) (Figure 1). Our aim here is to reflect on recent developments in environmental risk assessment by reference to regulatory practice in the UK and to highlight the opportunities that exist to transfer expertise between applications. We address (i) the use of tiered approaches to risk assessment; (ii) the application of risk rating systems for risk management resource-planning; (iii) the treatment of uncertainty for complex risks; and (iv) the use of risk scenarios. The implications of these issues on regulatory decision-making are discussed. Policy Context. The handling of “risk” by governments and their agencies has moved up the political agenda in the last 10 years. In the UK, a commitment to improve public policy in the handling of risk was made in the 1999 White Paper “Modernising Government” (9). UK government departments and agencies are preparing risk management frameworks, explaining how they assess, manage, and communicate the risks for which they have responsibilities (9, 10). The Department for Environment, Food and Rural Affairs (DEFRA) and the Environment Agency of England and Wales have responded (11) by (i) presenting recent developments in the policy and practice of environmental risk assessment; (ii) setting out their own approach; and (iii) communicating to practitioners and others their expectations of risk assessment work undertaken in support of environmental permitting. Revised DEFRA and Environment Agency guidance (11), updating previous advice (12), reflects the current debates in risk assessment practice and adopts many internationally accepted principles. Good problem definition, proportionality and consistency of approach, the explicit treatment of uncertainty, and presentational transparency are common themes (6, 10, 13). The guidance offers a generic, over-arching risk assessment-risk management framework (Figure 2) to which specific risk guidance, such as that for waste management regulation, historically contaminated land, flooding, and coastal defense, can refer (14). Recent developments in risk policy (9, 10) are benefiting from the emphasis on the social aspects of decision-making 10.1021/es011050m CCC: $22.00

Published 2002 by the Am. Chem. Soc. Published on Web 12/28/2001

FIGURE 1. A decision support framework for major accident hazard safety developed for the offshore oil industry (after ref 8, with permission). This has wide application beyond the process sector. The framework takes the form of a spectrum of decision contexts and accompanying tools ranging from those for conventional engineering decisions to those where corporate and societal values are seen as dominant factors. Groups of characteristics A-C are used to describe the decision context for the user and the balance of tools shown adjacent within the box. The means of checking these types of decisions are provided on the left-hand side of the box.

FIGURE 2. A framework for environmental risk assessment - risk management in the UK (11). The schematic provides an overarching framework to which approaches for specific hazards from flooding, waste disposal, and historically contaminated land can refer. (1, 2, 11-13), and, while not detailed here, this is having a growing influence on risk assessment practice. Calls for increased stakeholder and public involvement (1, 3, 4) are requiring greater access to risk assessments, and both national (UK) and international legislation is emphasizing consultation as a duty among public and governmental organizations. Following developments in the US, there is need in the UK for risk assessments to become more accessible to nonexpert audiences and available for critical evaluation and constructive challenge. How risk assessment practice responds to this agenda, while retaining its analytical power for decisionsupport, is developing into an important debate among practitioners and stakeholders. Tiered Approaches: From Project to Strategic Risk. Central to the UK approach to environmental risk assessment is the concept of proportionality (Figure 2) (11, 15). The “tiering” of assessment effort allows the degree of sophis-

tication in the analysis to be matched to the complexity of the problem and our understanding of the supporting science, so avoiding redundancy or misplaced precision. This applies whether one is concerned with individual risk problems at the project (16) or the strategic level (17, 18). For strategic analysis, where comparisons between risks quite different in character may preclude numerical analysis, qualitative screening and prioritization techniques (tier 1, Figure 2) are more appropriate (19). For high priority risks from welldefined hazards at the project scale, such as those arising from the disposal of radioactive waste in containment facilities, tailored quantitative risk assessment techniques may be more applicable (tier 3, Figure 2). Complex risks that involve well-described and/or less well understood aspects require a range of approaches and the means for meaningfully synthesizing qualitative and quantitative data. VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 3. Risk-based regulation attempts to optimize the cost of regulatory effort with risk, by shifting resources from low risk toward high risk activities, setting the level of inspection according to how the risk varies as a function of inspection (23-25). In targeting the inspection effort, and without losing sight of the performance of individual sites, the aim is to set inspection frequencies for all sites so that overall reductions in risk outweigh any individual increases in risk. One illustration of the above discussion lies in the development of waste management installations. Environmental risk assessment is fundamental to all phases of the development from the strategic planning level, where site screening and selection are progressed, through development planning and on to permitting where quantitative risk assessment helps identify risk management options required to mitigate risks from the installation. Risk management measures become stipulated as risk-based license conditions, for example, with respect to gas and leachate control. Following permitting, the routine inspection, monitoring, and review of such installations can be prioritized according to the degree of risk posed, so as to best utilize the regulatory resource for maximum risk reduction. Prioritizing Risk and Resourcing Risk Management. The UK strategy for sustainable development (20) emphasizes the need for effective environmental protection. Among the means of achieving this is the targeting of regulatory resources (time, human resources) through risk-based, or riskinformed, regulation (Figure 3). The use of risk ranking systems for informing risk management, particularly regulatory inspection, is well established (21, 22). For a set of common activities, this approach represents a “tradeoff” whereby regulatory attention on low risk activities is released for focusing on ones of higher risk. Risk ranking systems have their critics (22), but designed well, they can improve regulatory efficiency and offer incentives for better risk management (23-25). Targeting regulatory resources in this fashion requires a risk assessment for the subject under study, using a range of critical factors that contribute to the overall risk. For flood defense inspection, these factors might include the design 532

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standard, the physical condition of the defense, and the type of land-use protected. The selection and grouping of the individual risk factors is conducted according to the needs of the individual scheme (21). The Environment Agency’s operator pollution risk appraisal (OPRA) system (23), applied to the resourcing of regulatory inspections within the process sector, has risk factors grouped by the inherent pollution hazard posed by a facility and those dependent on the operator’s performance in managing the hazard. Identifying those factors within the control of the developer, operator, or regulator, and those factors less easy to control reflects the sensitivity of any factor to intervention and can help influence regulatory priorities and individual site responses to risk reduction. The design of risk ranking systems can be contentious because the scale of risk represented by scores is arbitrarys only the relative risk between facilities has meaning. One benefit of “scoring” over a qualitative descriptor of risk, however, is in distinguishing between probability and consequence contributions to risk, for example, in distinguishing between a hazardous process (consequence) and the performance of an operator in managing the potential risks posed by its operation (probability). A disadvantage is the potential abuse of the scores for purposes other than that for which they were designed. Experience in the US and UK demonstrates that these systems need to be simple, clear, piloted prior to wider use, and made reproducible. Having assessed the risk, resource allocation can be achieved, allowing for other considerations, by apportioning the available resource according to the grand sum of overall risks, or by assessing the grand sum and constructing a case for resources accordingly. A combination of resource “sup-

FIGURE 4. For many flood and coastal defenses in exposed locations, overtopping depends on both water level and wave height. Damage to a defense and the possibility of breaching is also related to the combination of loads. Joint probability (JP) approaches are used to estimate the probability of combinations of high water level (W) and wave height (H), shown simplistically as p(W,H) for a given combination. When combined with suitable “structure functions” such as formulas for overtopping or damage, JP analysis can be used to assess risks of flooding taking a wide range of load combinations into account. Similar principles apply to other cases such as combined tidal/fluvial effects. ply”- and “demand”-led approaches usually applies. Progressing to a demand-led approach raises important policy issues of comparative cost-benefit tradeoffs and equity in the relative allocation of resources for the management of quite different risks, such as, for example, flooding, historically contaminated land and local air pollution control. Initially, resources can be allocated in proportion to the risk levels assessed using the scoring scheme. With experience, as risks are reduced over time, the regulator can assess where resources are having greatest effect and where a resource surplus exists. Resource planning can then adopt a further aspect of targeting by turning attention on risk critical factors where reductions are most readily achieved. Dealing with Uncertainty. A principal outcome of recent risk episodes in the UK has been recognition of the need to be explicit about uncertainties (1, 26). Environmental risk assessments account for a range of uncertainties, and, for numerical risk estimates, the types of uncertainty addressed will influence the risk distribution. A number of classifications of uncertainty have been developed. One distinguishes between “epistemic” and “aleatory” uncertainties. Epistemic uncertainties are those associated with a lack of knowledge or of observational data and can be reduced through additional experiment or by provision of a greater data record. Aleatory uncertainties relate to those events for which there cannot be observational data, for example, future human actions. In this case, probabilities can only be defined through expert judgment, and there is no way of reducing the uncertainty at the time of assessment. One approach to the epistemic uncertainties associated with extremes within a data record is the joint probability method. The method also addresses a common, often erroneous presumption, which is that events, or the conditions that initiate a hazardous event, act independently. Joint Probability Studies. Many environmental risks are characterized by the consequences of rare or extreme events or by some combination of events. The Environment Agency and DEFRA have put significant investment into understanding environmental extremes. Extreme value (EV) analysis, which assumes that random processes drive a hazard, has been the basis of engineering design to resist environ-

mental loads, such as the extremes of wave height or water volume, for decades (27, 28). EV methods involve fitting a probability distribution to data on the variable of interest, and then extrapolating to a low probability, high consequence (extreme) event to help set design criteria, such as the crest height of flood defense structure or reservoir. However, often (i) the adverse consequences following an extreme event depend on a combination of loads, rather than on a single load; (ii) consequences other than those which the “design” mitigates against may be important; and (iii) there may be several different failure mechanisms to which the design is susceptible. Increasing pressure to understand the risks faced by society from natural hazards and extreme events has led to increased flexibility in methods for analysis and design. Consider coastal flood defense design. In England and Wales, some two million homes and businesses are located in areas at risk from flooding and coastal erosion. Many are dependent on defenses for protection without which the total potential annual average damages would be approximately £3 billion, with about 50% in sea or tidal risk areas. Here, defense structures must withstand combinations of high waves (surge) and high water (tidal highs). While they are unable to predict the precise combination of loadings that will occur, risk analysts and design engineers must account for the effects of different combinations of wave height and water level and their probabilities of occurrence. A key parameter for a coastal defense structure is the overtopping flow rate, expressed as a volumetric flow rate per meter run of a defense. This parameter has a direct effect on flood volume and area and is a good indicator of the likelihood and magnitude of structural damage to the crest and landward slope of the defense structure (Figure 4). Formulas can predict overtopping flow rates for a range of sea defense geometries. The combined influence of wave and water levels can be addressed in two ways. In the structure variable approach (SVA), the overtopping rate is calculated for each independent record of wave and water level conditions. Providing these variables are recorded concurrently, the sequence of overtopping can be ordered and extrapolated to the required extreme value. In the joint VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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probability approach (JPA), extrapolation is performed on the loads such as wave height and water level rather than the response parameters. This requires a complex, multivariate, distribution to be fitted, with extrapolation to obtain joint exceedence probabilities: the likelihood that the wave height and the water level exceed the height of the defense structure simultaneously, over a given time period. The value of the JPA approach is that it accounts for the dependence between variables. This can have a major impact on risk in some cases. A practical advantage is that it needs to be carried out only once at a particular site, although the multivariate distribution fitting is potentially more complex. Multiple failures can also be explored using Monte Carlo sampling to produce a long sequence of synthetic load conditions that matches the extremes of all the individual variables, and which incorporates their interdependence. A synthetic data set forms the ideal basis for the risk analysis of a defense structure having a number of possible failure mechanisms (29). At its simplest, a record-by-record check can then assess whether a failure condition is met for one or more of the prescribed mechanisms. The proportion of records registering a “failure” can then be converted to a probability of failure on an annual basis and compared with a risk acceptability criterion. This type of analysis is being increasingly favored as strategic approaches to the management of flood and erosion risk gain acceptance. These view flood and erosion systems at a larger scale, such as whole catchment or coastal cell. The first generation of catchment flood management plans are currently being produced in England and Wales. Decisionmakers managing risk in an integrated way will need better information on the spatial pattern of risk as well as on the contributions from different causes and processes: what is the combined probability of simultaneous flooding in neighboring catchments? What is the relative likelihood of extensive compared with localized flooding? and What is the probability of flooding due to long-term increases in groundwater levels combined with short-term heavy rainfall? The joint probability method is one way to examine these issues and has an important role in the integrated analysis of flooding problems and their solution. Presenting Risk Distributions. Presenting and communicating risk distributions is difficult, particularly where extreme values must be considered. This is especially the case where complex risks are being assessed, at least in part, by reference to a single numerical criterion. One UK example is in the licensing of land disposal facilities for low and intermediate level radioactive waste. A risk assessment is central to the post-closure safety cases for such facilities (30). Briefly, the known features of the disposal facility, together with the processes and events that are reasonably certain to occur, can be used to predict its normal or expected behavior over time. The overall consequences of the interactions between these high-probability processes and events, with the associated uncertainties, determine whether the expected behavior of the facility is tolerable in terms of risk. The system can also be affected by further events, faults, or accidents that have lower probabilities of occurrence and where the associated uncertainties are aleatory, such as inadvertent human intrusion into the facility at some point in the future. These events can result in adverse consequences greater than would be expected under normal behavior, and their contribution to the overall radiological risk over time is dependent on expert, but subjective judgments of their probability (30-32). Current regulatory guidance (33) for applications to dispose of low and intermediate level radioactive waste to land adopts an upper bound individual risk target of 10-6 per year (above background, annual increase in the likelihood of a radiological-induced health effect) in the period after closure of the facility. This represents the radiological risk 534

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FIGURE 5. Schematic illustration of how the mean and other measures of central tendency vary with the form of the distribution. In decision-making, the mean estimate can be significantly affected by extremes within a distribution. This can particularly be the case when considering very long timecales when future events may be speculative. from the facility to a representative member of the potentially exposed group at greatest risk. Typically, safety cases for disposal facilities express distributions of dose or risk, and this presents the problem of collapsing the distribution to a single value for comparison with the regulatory risk target. One approach is to present the arithmetic mean, or “expectation value” of the risk. Others include presentation of the median (50th percentile), the 90th or 95th percentiles, or the mode (Figure 5). The expectation value is sensitive to changes at the high-end of the distribution, and requires an arbitrary integration limit for distributions that cannot be integrated analytically. In the context of risks relating to longterm safety over hundreds of thousands of years, the expectation value has disadvantages in that the risk is calculated as a function of time for each of many sets of events (futures). Each future may involve different exposed groups, in which case, averaging across futures becomes inappropriate. Even for similar groups, estimated risks may be “diluted” if different futures give rise to peak risks at slightly different times (32). Loss of information on the shape of a distribution when collapsed is especially important for highly skewed distributions (Figure 5b,c) where low probability, high consequence (extreme) events dominate the mean. These situations might arise from, say, the impact of extreme climate events. In Figure 5c, the distribution might represent the impact arising

FIGURE 6. Methodology for the assessment of the potential effects of climate change on source yield. The figure summarizes for decisionmakers the sequential methodological steps for estimating future water resource yields under the influence of climate change. from normal behavior of a waste repository with high consequence events arising from, for example, possible future human intrusion. In such cases, use of the expectation value could be misleading unless information on the form of the distribution is presented, together with a discussion of the level of confidence attached to the risk estimates. Presentation of conditional risks and the separation of different types of uncertainty aid regulatory decision-making and may assist stakeholder dialogue (34) where “what-if” calculations are presented for different risk scenarios and futures. Scenario-Based Approach to Management Decisions. The scenario approach is now in wide use for assessing the possible impacts of climate change, generally using the output of global climate models (GCMs) (35). While scenario-based analyses can be scientifically satisfying, their application to management decisions can sometimes be limited. The spatial and temporal resolution of the scenarios is often inappropriate for modeling impacts and arguably for the decisionprocess itself. Most business planning horizons are far shorter than the single time horizon used for climate change scenarios, which conventionally look to the 2020s or 2050s. Further, the current data from GCMs provide little information on changes in the frequency and magnitude of extremes, and it is often changes in the nature of this type of event that have the greatest impact. These uncertainties create problems where long-term financial investment is required, or where there is an aspect of irreversibility about a management decision. The lack of information on the probability of the

scenarios, or the ability to provide a “best-guess”, compounds these problems. Use of a single scenario, be it the central estimate or the “worst case”, may make good business sense but may not provide a basis for sound investment decisions because of the inherent model uncertainty (36). One example of a scenario-based approach to asset management is the management of investments by the UK water industry. In 1996, the then Department of the Environment required the water industry to take account of climate change in its future asset management plans (37). Water resource managers required a rapid, strategic-level assessment of climate sensitivity, so that a range of climate futures could be applied to the water resource base, and impacts on regional supply compared (38, 39). Despite the uncertainties associated with climate change scenarios, a core set was used as a consistent basis for water resource planning to inform estimates of future investment, the potential need for water abstraction schemes and reservoirs, for example. The methodology developed (Figure 6) presents the user with a series of tasks selected according to the available modeling capability. Ideally, the water resource manager works with an appropriate hydrological model (catchment or aquifer) to assess resource yield. In these cases, the standard Intergovernmental Panel on Climate Change (IPCC)-recommended impact analysis could be carried out as in the left-hand trunk of Figure 6. The driving variables are rainfall, temperature, and potential evaporation. These are perturbed to represent future conditions, estimated VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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FIGURE 7. Average change in monthly runoff for the six UK regions under just one climate change scenario for the 2020s as compared to the 1961-1990 conditions. The schematics provide a visual impression of the potential impact of climate change in regional catchments. Decision-makers can apply these factors to historic data in determining the impacts of climate change on source yield (as in Figure 6). monthly averages by the 2020s, according to the core set of scenarios. The model is run under perturbed conditions, and the resulting yield is compared with that under the current climate. In practice, models exist for only a small proportion of supply sources, and considerable effort would be required to develop, calibrate, and apply them for all sources. Therefore, a fast-track, screening approach provided a broad indication of the vulnerability of source yields to climate change (39). This involved application of regional factors for changes in yield, from groundwater recharge and streamflow, to observed recharge and flow data. The UK was divided into six regions, broadly based on the boundaries of the UK Hadley Centre global climate model (40). For each region, flows were simulated in a number of catchments under current, and a range of possible, future climate conditions. The regional factors were then determined as the average changes in monthly flow. The regional factors in groundwater recharge were determined from the results of an aquifer recharge model run for a small number of groundwater-dominated catchments. 536

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The result of this analysis was a set of perturbed flow series indicative of conditions under the changed climate of the 2020s. The results for one of the climate change scenarios, for the six regions, are presented in Figure 7, showing the average change in monthly runoff for the 2020s. The potential reduction in late summer/autumn runoff is clear in the South, as is the possible increase in flows throughout the year in northern England, Scotland, and Northern Ireland. What is not clear is the degree of variability between the scenarios. In some regions, runoff increased under some scenarios and decreased under others. Further, at present, it is not possible to highlight the “best-guess” scenario. This approach provided water managers in the UK with a pragmatic tool for undertaking a rapid screening of the potential risks from climate change on water resources in the light of significant uncertainty. As with all scenario-based approaches, the methodology carries with it a number of assumptions and caveats, of which the decision-maker, water managers in this case, should be aware. Importantly, the regionally averaged factors hide a substantial amount of within-region variability but in this case, it was felt that to

further subdivide into smaller regions would considerably compromise practical application of the method.

Discussion Risk assessment is one tool among many used to support decisions about managing the environment, within a broader framework of cost-benefit analysis. Others include environmental appraisal, multi-criteria analysis and game theoretical approaches (41, 42). Further, the development of environmental risk frameworks is not new. Their value is in showing the relationships between different stages and components of the decision, and so they have an important role in improving the transparency of decisions. What is new is the increasing attempts made by risk analysts to cross-fertilize between different contexts of application. We have provided some examples of where such transfer of expertise is taking place. Others include (i) in the use of “risk registers” during hazard identification, initially developed for hazard and operability (HAZOP) studies in the chemical industries (43); (ii) the increasing use of formal expert elicitation techniques in environmental exposure assessment, adopted widely for the performance assessment of radioactive waste repositories (44); and (iii) the use of failure mode and effect analysis (FEMA) developed within the process industries, for the microbiological risk assessment of pathogens in the environment (45). Risk analysts increasingly work in multidiscipline teams to address risk problems, the characteristics of which often extend beyond the technical characterization of the hazard under study. The Environment Agency’s National Centre for Risk Analysis and Options Appraisal is making important strides forward in this regard by developing more integrated approaches. Among the interdisciplinary “transfers” being addressed here are (i) the role of uncertainty in climate change impact assessment and in environmental appraisal, which have historically been impact- rather than truly risk-led; (ii) developments in our understanding of environmental harm, considering damage characteristics such as latency, reversibility, and heterogeneity that are often disregarded in risk analysis; and (iii) the importance of “framing” during the problem definition stage of risk assessment and, in particular, the influence of stakeholder agendas in setting the context for environmental risk assessment. The emergence of the social issues agenda as a key driver for sustainable development in the UK is having a real impact on environmental decision-making. Along with the US and the rest of Europe, the UK is witnessing a move toward integrated decision-making, taking jointly into account the social, environmental, natural resource, and economic aspects of environmental management problems. Flood and coastal defense provides an excellent illustration of where these considerations collide. For those designing to a particular standard, or appraising the risks, costs, and benefits of alternative options for defense structures, the type of joint probability analysis described above provides a comprehensive description of loads and failure mechanisms leading to improved solutions. The benefits are economically robust solutions more closely matched to an improved risk analysis of the imposed loads. The approach is being widely applied, particularly for design of structures along the coast and in estuaries. This move toward integration is forcing a re-appraisal of the capabilities and limitations of individual decision tools (46). The practical nuances and differing emphases of individual tools in terms of the level of detail at which they are optimally applied, the extent to which they address the various aspects of environmental decisions, and the degree to which they address uncertainty and wider societal values are all under debate. In response, decision-makers are developing a “palette” of decision analysis tools for dealing with individual risk problems (47). There are also signs that

the concerns of nongovernmental organizations with respect to environmental risk assessment are being addressed in part by greater stakeholder participation in risk assessment processes (48-50). It is clear that the integration being experienced between risk analysts now needs to progress with practitioners of other appraisal tools in the broader context of sustainable development. One challenge for risk analysis as a discipline is how to respond to this policy agenda while maintaining and developing an analytical rigor that can address environmental issues of deep uncertainty. Environmental regulators have a range of responses at their disposal for managing pressures from, or on, the environment. Modern approaches to environmental regulation attempt to match the regulatory response to an operator’s performance and attitude, using influence and education to deliver outcomes, wherever possible underpinned by regulation. In practice, this means using a minimum of administration and bureaucracy to greatest effect, retaining firm and proportionate prosecution and enforcement policies and standardizing and simplifying decisions where possible. The move toward “risk-informed” regulation that allows the targeting of inspection and monitoring effort has been welcomed by government and industry (21, 23, 51) and, in principle, allows for resources to be released for other influencing activities. The Environment Agency’s experience in applying risk-ranking systems for individual business sectors is now being extended to the recently introduced integrated pollution prevention and control (IPPC) regime that offer an opportunity to apply risk appraisals within and between business sectors. Notwithstanding the considerable challenge of comparing between quite disparate risks, the application of these systems may ultimately offer a “bottomup” approach to setting to regulatory priorities that can complement the “top-down” assessments informed by state of the environment reporting. Finally, the need to be explicit about uncertainty in risk analysis (52) has long been recognized and is a recurrent theme for policy analysts and risk practitioners. Being clear about those uncertainties that can be addressed through more observation and experiment and those that cannot is a start, but clearly the debate needs to deliver us to a point where we can be more comfortable about decision-making under circumstances of complexity and extreme uncertainty. Gradually, this is happening. Developments in risk analysis are influencing policy directions, informed by the analysis described above for water resource planning, the Environment Agency’s new water resources strategy assumes no change in the national water supply over the next 20 years, there being sufficient current or planned capacity. Instead, the Agency has chosen to emphasize the demand side of the water balance, both in terms of changes in demand due to climate but also other socio-economic factors. Practical, accessible tools for decision-makers (53) like those described that can be integrated alongside accepted business and planning processes are required if we are to make genuine progress.

Acknowledgments The opinions expressed are the authors’ alone. We acknowledge permission from DEFRA and the Environment Agency to publish and the valuable comments of government colleagues and anonymous peer reviewers made during preparation.

Literature Cited (1) Royal Commission on Environmental Pollution, Cm 4053, Twenty-First Report: Setting Environmental Standards; The Stationery Office: London, UK, 1998. (2) House of Lords, Select Committee on Science and Technology 1999-2000, Third Report. Science and Society, HL Paper 38; The Stationery Office: London, UK, 2000. VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY

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Received for review June 8, 2001. Revised manuscript received October 15, 2001. Accepted October 23, 2001. ES011050M