Coastal flood risk is a function of the probability of coastal flooding and the consequential damage. Scenarios of potential changes in coastal flood risk due to changes in climate, society and the economy over the twenty-first century have been analysed using a national-scale quantified flood risk analysis methodology. If it is assumed that there will be no adaptation to increasing coastal flood risk, the expected annual damage in England and Wales due to coastal flooding is predicted to increase from the current £0.5 billion to between £1.0 and £13.5 billion, depending on the scenario of climate and socio-economic change. The proportion of national flood risk that is attributable to coastal flooding is projected to increase from roughly 50% to between 60 and 70%. Scenarios of adaptation to increasing risk, by construction of coastal dikes or retreat from coastal floodplains, are analysed. These adaptations are shown to be able to reduce coastal flood risk to between £0.2 and £0.8 billion. The capital cost of the associated coastal engineering works is estimated to be between £12 and £40 billion. Non-structural measures to reduce risk can make a major contribution to reducing the cost and environmental impact of engineering measures.
The coast of England and Wales contains a concentration of population and industry, together with environmental and recreational assets. Large urban areas, including London, and significant proportions of high-grade agricultural land are located in coastal floodplains. In addition to the risk of flooding in the coastal lowlands, the UK has many eroding coastlines, the total length of which has recently been estimated to be over 3000 km (Eurosion 2004). The UK vulnerability is indicated by the fact that it has around 2300 km of artificially protected coast, the longest in Europe (Eurosion 2004).
Using results from the Hadley Centre's HadCM3, Hulme et al. (2002) predict that by the 2080s and depending on the greenhouse gas emissions scenario, relative sea-level may be between 2 cm below and 58 cm above the current level in southwest Scotland and between 26 and 86 cm above the current level in southeast England. For some coastal locations a water level that at present has a 2% annual probability of occurrence may have an annual probability of occurrence of 33% by the 2080s for medium–high emissions. These estimates do not account for uncertainty in regional assessments of sea-level rise or for any change in the frequency of storm surge residuals.
In 2004, the UK government published the results of a 2 year Foresight project on flood and coastal defence (Evans et al. 2004a,b). The aim of the project was to analyse the risk that flooding and coastal erosion poses to the UK over a time-scale from 2030 to 2100. The analysis proceeded through a combination of consultation, structured expert elicitation and quantified risk analysis. The Foresight project dealt with flooding from rivers and the sea in an integrated analysis framework. In this paper, we make use of the modelling conducted as part of Foresight to present new analysis specifically of coastal flood risk and vulnerability to climate change. The quantified analysis is restricted to England and Wales because it makes use of the Environment Agency's National Flood and Coastal Defence Database, which does not include Scotland and Northern Ireland.
The focus of the work is on flood risk, but the Foresight study and other research has highlighted the influence of coastal erosion on modifying flood risk both locally and on down-drift coasts. The Foresight study confirmed previous analysis (Halcrow 2001) that, on its own, coastal erosion is not a major economic issue. Coastal erosion losses represent only just over 3% of the total risk, although this is based upon an average estimation of property numbers (value £7.7 billion at 2000 prices). Even taking the extreme property number estimates, for which asset values vary between £2.7 and £12.2 billion, this still only represents 2–6% of the total capital value of assets at risk (Halcrow 2001). However, in the context of broader coastal zone management issues and also the viability of coastal settlements on eroding coastlines, coastal erosion merits serious attention.
This paper begins with a review of the evidence relating to marine climate change on the UK coast. The coastal flood risk analysis method is introduced, which was in the first instance used to estimate the total expected annual damage due to coastal flooding in England and Wales, based on data for 2002. The parameters in this flood risk analysis method were then perturbed to reflect the effects of scenarios of future climate and socio-economic change. This method was first applied in the Foresight study (Evans et al. 2004a,b), but new results are presented that have been generated subsequent to the Foresight study, based on the same analysis methodology, scenarios and datasets. The scenarios analysis first deals with the base line situation in which it is assumed that there is no adaptation to climate or socio-economic change. In other words, current coastal management practices were projected into the future more or less unchanged. Flood risk estimates, again in terms of expected annual economic damage, are presented for four scenarios and compared with the present day risk estimate. Then scenarios of future coastal management, which were implemented by modifying the coastal defences, land use and other variables in the flood risk model, are presented to investigate the potential for adaptation to future changes. We conclude by reflecting on the usefulness of the methodology and the implications of the results.
2. Marine climate change in the UK
It is estimated that, by the 2080s, the global average sea-level will have risen above present day levels by between 90 and 690 mm, depending on emissions scenario (Hulme et al. 2002). Such predictions require translation to provide regional estimates of sea-level rise. Tsimplis et al. (2005) provide multiplication factors for this. They also include a means of accounting for the effect of fluctuations in the North Atlantic Oscillation (NAO).
The risk posed by ongoing sea-level rise depends on the magnitude and frequency of surge events. Hulme & Jenkins (1998) provide a design method in which the net sea-level rise is added to water level frequency curves calculated from historic data. This approach assumes stationary surge statistics, while some evidence suggests that extremes are increasing (e.g. Langenberg et al. 1999). It also does not account for the effects of increased sea-level on tide and surge propagation and on surge generation. Lowe et al. (2001) modelled storm surge for both existing conditions and the climate in 2100, using a 35 km resolution model of the northwest continental shelf region. The results show an increase in 1 : 50 year return period events for most of the British coast. This increase ranged up to 0.24 m. Debernard et al. (2002) conducted a similar analysis of wind, wave and storm surge climates in the northern North Sea. Present day and future (2030–2050) conditions were modelled, driven with output from regional climate models. The results showed relatively small changes, but rougher autumnal maritime climates.
It is widely held that there has also been a significant growth in wave conditions in the North Atlantic (NA) over the last few decades. Bacon & Carter (1991) demonstrated recent growth in NA mean wave height of about 2% per year. Subsequently, Bacon & Carter (1993) related wave observations to the NAO and were then able to tentatively hindcast wave conditions to 1873 for the northeast Atlantic. These results indicated that the observed growth in wave height began in the mid-1960s and had not been exceeded during the hindcast period. Gulev & Hasse (1999) calculated similar increases in wave height of between 100 and 300 mm decade−1. The WASA group (1998) studied the apparent rise by analysing 40 years of wind records and using them to hindcast wave conditions, concluding that the storm and wave climate in the North Sea and most of the northeast Atlantic has shown significant variability at decadal time-scales and has become more energetic in recent decades. However, recent storm intensity is similar to that experienced at the start of the twentieth century, so present storminess may simply be an expression of natural climate variability. There is some evidence that the period of wave height growth may be coming to an end. Langenberg et al. (1999) found Baltic sea storms to have calmed in recent years. The WASA group (1998) explored the relationship between climate variability and the NAO. More recent work (Wolf et al. 2002) investigated the relationship between recent wave heights and the NAO. This relationship is useful in that it provides a means of linking wave predictions with large-scale climate changes. Tsimplis et al. (2005) discuss this in some depth and stress the uncertain nature of wave predictions, but are able to provide scenarios of future wave conditions around the British Isles for the 2080s in terms of growth in significant wave height.
Hargreaves et al. (2002) explored the coastal wave conditions around the British Isles resulting from a continued increase in offshore wave conditions and sea-level rise. It was found that the relationship between offshore and inshore waves was complicated by bathymetry, tidal range and wave angle. Sutherland & Gouldby (2003) used General Circulation Model (GCM) and surge model data to demonstrate the relative effects of increased mean sea-level, future wave climates, raising the crest height of a seawall and coastal steepening on overtopping. Burgess & Townend (2004) have observed that most of the UK's sea dike structures have depth-limited design wave conditions, which implies that the largest nearshore waves may not increase if offshore waves do. It should be noted, however, that larger waves are likely to drive coastal morphology at a greater rate so, over the medium to long term, any growth in offshore wave heights may well be expressed at the coast.
3. Quantified national-scale analysis of coastal flood risk
Flood risk is conventionally defined as the product of the probability of a given flood event and the consequential damage, integrated over all possible flood events. It is often quoted in terms of an expected annual damage, which is sometimes referred to as the ‘annual average damage’. Significant progress has been made in recent decades in the development of probabilistic flood risk analysis methods for the coast at the scale of Dutch dike ring systems (Vrijling 2001; Voortman et al. 2003). However, these methods are limited by the availability of data, in particular relating to the configuration of sea dike systems. The analysis presented in this paper is based on an approximate national-scale methodology (Hall et al. 2003) developed to make use of the following Geographic Information Systems (GIS) databases for all of England and Wales:
Indicative Floodplain Maps (IFMs) are the only nationally available information on the potential extent of flood inundation. The IFMs are outlines of the area that could potentially be flooded in the absence of defences in a 1 : 200 year return period flood for coastal floodplains.
1 : 50 000 maps with 5 m contours: The methodology has been developed in the absence of a national topographic dataset of reasonable accuracy. Topographic information at 5 m contour accuracy has only been used to classify floodplain types as it is not sufficiently accurate to estimate flood depths.
National flood and coastal defence database provides a national dataset of dike location, type and condition.
National database of locations of residential, business and public buildings.
Land use maps and agricultural land classification.
An essential aspect of flood risk analysis is to assess the reliability of sea dikes. These infrastructures must be dealt with as systems if the flood risk is to be accurately estimated. In the absence of more detailed information on flood extent, the Indicative Floodplain is adopted as the maximum extent of flooding and is further sub-divided into Impact Zones not greater than 1 km×1 km. Each flood Impact Zone is associated with a system of sea dikes which, if one or more of them were to fail, would result in some inundation of that zone.
Reliability analysis of coastal dikes potentially requires a huge quantity of data, which are not available for all of the dikes in England and Wales. An approximate reliability method has, therefore, been developed that makes use of the so-called standard of protection (SoP), which is an assessment of the return period at which the dike will significantly be overtopped. The dike is addressed by estimating the probability of failure of each dike section under a given load (relative to SoP) for a range of load conditions. Generic versions of these probability distributions of dike failure, given load, have been established for a range of dike types for two failure mechanisms: overtopping and breaching.
Having estimated the probability of failure of individual sections of dike, the probabilities of failure of combinations of dikes in a system are calculated. To do so, it is assumed that the probability of hydraulic loading of individual dikes in a given dike system is fully dependent. The probabilities of failure of each of the dikes in the system, conditional upon a given load, are assumed to be independent. For each failure combination, an approximate flood outline which covers some proportion of the IFM is generated using approximate volumetric methods. These methods estimate discharge through or over the sea dike and inundation characteristics of the floodplain.
In the absence of water level and topographic data, estimation of flood depth has been based on statistical data. These data were assembled from 70 real and simulated floods for a range of floodplain types and floods of differing return periods. These data were used to estimate flood depth at points between a failed dike and the floodplain boundary in events of a given severity. Flood depth estimates from a range of floods were used to construct an estimate of the probability distribution of the depth of flooding for each Impact Zone.
The numbers of domestic and commercial properties and the area of agricultural land in each Impact Zone were extracted from nationally available databases. These data were combined with relationships between flood depth and economic damage that have been developed from empirical analysis of past flooding events (Penning-Rowsell et al. 2003). For a given Impact Zone, the expected annual damage R is given bywhere ymax is the greatest flood depth from all flooding cases, p(y) is the probability density function for flood depth and D(y) is the damage in the Impact Zone in a flood of depth y metres. The total expected annual damage for a catchment or nationally is obtained by summing the expected annual damages for each Impact Zone within the required area.
Figure 1 is based on the IFMs and illustrates how coastal floodplains in England and Wales are concentrated on the south and east coasts. Several of Britain's main metropolitan areas, most notably the financial districts of London, are located within this floodplain. Large areas of high-grade agricultural land in the east of England are located in coastal floodplains. The floodplains are identified as being liable to coastal flooding on the basis of the Environment Agency classification. Some areas classified as being fluvial (so not appearing in figure 1), notably the Fens of East Anglia, might also be liable to coastal flooding, especially under sea-level rise scenarios.
Based on the methodology outlined above, the Expected Annual Damage due to coastal flooding in England and Wales was estimated to be £0.5 billion. This represents roughly half of the flood risk due to fluvial and coastal flooding combined, as estimated in 2002. The highest economic risk is located in floodplain areas of high economic value, notably central London (despite very high standards of flood protection) and Hull (figure 1). The expected annual coastal flood damage to agriculture, which is small compared with damage to buildings and contents, is estimated to be £2.2 million, representing 37% of the total expected annual flood damage to agriculture.
4. Scenarios of future coastal flooding
The use of scenarios for policy analysis far into the future has been stimulated by the long-term nature of climate change and the socio-economic uncertainties surrounding greenhouse gas emissions and projections of societal vulnerability. Coastal flooding is an interesting application of the scenarios-based approach because it involves integrated use of two different types of scenario:
Climate change projections are based on emissions scenarios.
Socio-economic scenarios provide the context in which coastal management policy and practice will be enacted and influence the vulnerability of the coast to climate change.
The climate impacts analysis has been based upon the UKCIP02 climate scenarios for the UK (Hulme et al. 2002; table 1). These scenarios are based on runs of the Hadley Centre's HadCM3 GCM, dynamically downscaled to the UK using the HadRM3 regional climate model. The UKCIP02 scenarios are presented in terms of four emissions scenarios: low emissions, medium–low emissions, medium–high emissions and high emissions corresponding to the IPCC's SRES (IPCC 2000) scenarios B1, B2, A2 and A1FI, respectively. Of most relevance to the coastal analysis are projections of sea-level rise. No conclusive patterns of spatial variability are detectable in comparisons of GCM predictions of sea-level rise. Therefore, projections of absolute mean sea-level rise, globally averaged, have been super-imposed upon rates of land subsidence/emergence measured for the UK.
The Foresight Futures socio-economic scenarios (SPRU et al. 1999; DTI 2002) are intended to suggest possible long-term futures, exploring alternative directions in which social, economic and technological changes may evolve over coming decades. The four Foresight Futures are summarized in table 2.
There is no direct correspondence between the UKCIP02 scenarios and the Foresight Futures 2020, not least because the Foresight Futures are specifically aimed at the UK, whereas the emissions scenarios used in UKCIP02 are global emissions scenarios. However, an approximate correspondence can be expected, as shown in table 1. This is not the only conceivable correspondence and several alternatives are explored by the UK Climate Impacts Programme (2000), Arnell et al. (2004) and Holman et al. (2005a,b).
The coastal flood risk analysis outlined above was used to calculate the effects of climate and socio-economic change by making appropriate modifications to the model parameters to reflect the time and scenario under consideration. The input data required by the coastal flood risk analysis did not correspond exactly to the information provided in either climate change or socio-economic scenarios. It was therefore necessary to construct approximate relationships between the variables for which scenarios information was available and those required for flood risk analysis. A summary of the relationships adopted in the analysis of risks from coastal flooding is provided in table 3. A quantified estimate was made of the effect in each scenario that a given change, for example urbanization, would have on the relevant variables in the risk model. The cumulative effect of each of the changes in the given scenario was then calculated. Where feasible, regional variation was applied to these adjustments in order to take account of, for example, differences in climate or demographic projections. For instance, table 4 illustrates variation in the effective SoP of different types of sea dikes under scenarios of climate change.
Future coastal risk is greatly influenced by coastal management policy and practice, perhaps more so than it is by changes such as climate change or economic growth outside the control of the coastal manager. In the first instance, current sea dike alignment and levels of investment in maintenance and renewal were kept the same across all scenarios. In other words, it was assumed that there would be no adaptation to climate or socio-economic change or in response to increasing flood frequency. Scenarios of adaptation are examined later in this paper.
5. Results of the scenarios analysis, assuming no adaptation
The results of the flood risk scenarios analysis are summarized in table 5, which compares the new analysis of coastal flood risk with the Foresight results for combined fluvial and coastal flooding. No discounting or inflation is applied to economic risks. Risk is estimated at time points in the future using today's prices.
A large increase in the number of people occupying coastal floodplains in the UK are envisaged in the relatively loosely regulated World Markets and National Enterprise scenarios. Most of this increase is predicted to occur by the 2050s, representing predictions in the first half of this century of very rapid growth, which is envisaged to approach a limit associated with a fairly stable population and spatial constraints. Floodplain occupancy is kept stable in the global sustainability and local stewardship scenarios. However, increasing coastal flood frequency, primarily due to climate change, means that, even with stable numbers of people in the floodplain, the number of people at risk from flooding more frequently than 1 : 75 years will increase in all scenarios, assuming that there is no adaptation in response to this increasing flood frequency. Greater climate change by the 2080s, together with the increased floodplain occupancy noted above mean that the World Markets and National Enterprise scenarios will see a doubling of the number of people at risk from coastal flooding more frequently than 1 : 75 years.
In all scenarios, annual economic damage from coastal and river flooding is expected to increase considerably over this century, assuming no adaptation. The magnitude of the increase is highly scenario-dependent and greatest in the World Markets scenario, which is attributable to a combination of much increased economic vulnerability (higher floodplain occupancy, increased value of household/industrial contents, increasing infrastructure vulnerability) together with increasing flood frequency.
The risk of coastal flooding will increase more than fluvial flood risk. While at present coastal flood risk is approximately equal to the economic risk from fluvial flooding, by the 2080s, 60–70% of the total risk will be attributable to coastal flooding, assuming no adaptation. More intensive rainfall is predicted for winter months in the UK, increasing fluvial flood risk (Evans et al. 2004a,b). However, the combined effects of sea-level rise and increased storminess mean that the effectiveness of flood protection systems on the coast will decline more rapidly. This increase in the probability of flooding is combined with a relative increase in coastal floodplain occupancy in most scenarios.
Figure 2 shows the distribution of the increase in expected annual economic damage for the 2002 analysis and the four scenarios for the 2080s relative to the estimated risk in 2002. Increasing risk is predicted to be concentrated in broadly the same areas as where it is currently highest, but without the added influence of higher relative sea-levels in southeast England. The sensitivity of the low-lying Humber estuary to sea-level rise is also noticeable.
6. Adaptation scenarios
The analysis described in the previous section was based upon the assumption that present day coastal management practices and standards of coastal flood protection are continued in future. In fact, these practices and standards will be modified in response to changing risks and society's expectations for risk reduction. In other words, coastal management policies and practices are scenario-dependent. In order to analyse the amount by which the risk estimates presented above may be reduced, a set of coastal management scenarios were established. These represent portfolios of policies and practices intended to manage the probability and consequences of coastal flooding and erosion. Table 6 summarizes the approaches to coastal management under the four scenarios. These scenarios are not policy prescriptions; they are merely intended to illustrate in an internally consistent way alternative plausible futures in order to inform long-term decision making.
The World Markets scenario is the wealthiest of the scenarios: by the 2080s, gross domestic product (GDP) could be 10 times (in real terms) its present value. This, therefore, is a wealthy society that can afford to protect against the risks to which it is exposed. There will be a tendency to provide coastal management (and many other services) through markets rather than through government. This means that protection against the risks of flooding will to a great extent be determined by ability to pay. Protection of the environment will also be increasingly privatized, with those environmental assets and services that generate economic rents being protected and enhanced. An emphasis on economic efficiency and relative neglect of environmental considerations means that in the World Markets scenario flood management will be dominated by hard engineering measures. These will be combined with the fruits of technological progress, for example in the field of communications.
The National Enterprise scenario is less wealthy than the World Markets scenario and more inward in its outlook. However, it is still a consumerist-oriented scenario with economic development rated as more important than environmental quality of coasts. It will be characterized by piecemeal and reactive coastal engineering measures. Emphasis will be upon protection of strategic industries, including agriculture.
In the Global Sustainability scenario, government plays a leading role in providing a range of structural and non-structural measures for coastal management, ranging from regulation of development to measures to help recovery after flooding, particularly for more vulnerable sectors of society. Society is willing to forgo some economic benefits, for example in terms of unlimited urban development, in order to reduce risks and share them more equitably. Flood dike engineering is employed, particularly in dense urban areas, but there is an emphasis on soft engineering to work with, and where possible restore, natural processes. There is emphasis upon monitoring of and adaptation to change and implementation measures that are resilient to future uncertainties.
The Local Stewardship scenario is characterized by regionally devolved and, at the same time, environmentally conscious approaches to coastal management. A variety of approaches are envisaged across different regions of the UK. Growth in national wealth is lowest in the Local Stewardship scenario, and is not expected to keep pace with the rate of increase of coastal flood risk. A consequence will be abandonment of some coastal floodplains, with communities working to reinstate natural systems. At the same time there is an emphasis on agricultural self-sufficiency, so some key agricultural land will be preserved regionally.
The adaptation scenarios described above and in table 6 were implemented by modifications to the database of coastal dikes and floodplain use and occupancy, representing the effect of structural and non-structural measures. Structural measures vary in importance according to scenario, but are included to some extent in each scenario and were implemented in terms of changing SoP provided by coastal dikes. The starting point was the current standards, which are expressed in terms of an indicative range (table 7). A land use band A* has been added to the customarily used land use bands (A to E) to reflect the particularly high standard of tidal flood protection in London.
The baseline analysis showed that economic damage, assuming no adaptation, will be greatest in the World Markets and National Enterprise scenarios because of increasing probability of flooding, the growth in value of areas at risk of flooding and because of the more flood-vulnerable nature of development. However, taking the scenarios as a starting point, we also believe that social and individual expectations for risk reduction in these more consumerist-orientated scenarios will be higher. Balanced against this is the question of affordability. For instance, under the National Enterprise scenario the resources available for flood protection are likely to be smaller due to lower economic growth (GDP growth per annum in the 2050s is taken as +1.75% as opposed to +3% for World Markets (UKCIP 2000)), and this will feed through into lower SoP. Resources for coastal management will be further stretched in the National Enterprise scenario by the need to protect strategic industries, including agriculture.
In the Global Sustainability scenario and, in particular, the Local Stewardship scenario, coastal flood risk is projected to increase at a slower rate so there will be less societal expectation for risk reduction. On the other hand, the Global Sustainability scenario will be characterized by government efforts to manage risks to people and the environment in a concerted and pre-emptive way. Standards of flood protection in the Local Stewardship scenario may show a great deal of national variation, reflecting local decision making, a feature that is impossible to represent in table 7.
In the globalized scenarios (World Markets and Global Sustainability), there will be much less emphasis on agricultural production than in National Enterprise and Local Stewardship. This is reflected in a withdrawal of flood protection from agricultural land other than of a high grade. The mechanism of this withdrawal will, however, be different, and is envisaged to occur in an unmanaged fashion in the World Markets scenario while it will be managed and accompanied by environmental restoration measures in the Global Sustainability scenario.
The changed coastal management practices and SoP were implemented in the databases of coastal dikes. Table 8 presents the statistics of how coastal dike standards were modified in the adaptation analysis. The one-off capital costs of these modifications were estimated using typical present day capital costs of works (Evans et al. 2004a,b) so do not reflect changes in future productivity of the construction industry, which will be scenario-dependent. The costs represent the typical total capital cost of constructing a new coastal dike and include design and supervision costs but exclude costs associated with land purchase, compensation or significant environmental mitigation measures. Maintenance costs are also excluded. The costs are presented as one-off upgrade costs and no consideration is given to the timing or phasing of these works. Recall also that these are costs only of dike raising, and costs of the other measures listed in table 6, for example the opportunity cost of restricting development in floodplains, have not been evaluated.
Costly engineering work is expected to take place on the south and east coasts of the UK. The total cost of engineering works (table 8) is about three times greater in the World Markets and National Enterprise scenarios than it is in the Global Sustainability and Local Stewardship scenarios. This reflects the greater rate of increase in risk in these scenarios and the increased reliance on engineering measures as opposed to non-structural flood risk reduction measures, which are not included in the costing.
Further evidence of increasing costs of coastal flood protection was provided by Burgess & Townend (2004), who estimated that by the 2080s the annual cost of coastal dike structures will be between 150 and 400% of the current levels (depending on the emissions scenario). Costs were less sensitive to geographic location than to emissions scenario. The costs were predicted to increase because structures were found to be very vulnerable to increases in water depth. This is because the design wave condition for most UK coastal dike structures is depth-limited. The height of this wave therefore increases linearly with water depth.
The results of the coastal flood risk analysis, including adaptation, are given in table 9. Both the probability of flooding and the associated flood risk have been substantially reduced. The magnitude of the reduction is greater in the World Markets and National Enterprise scenarios, reflecting the higher investment in engineering works under these scenarios. Despite withdrawal of flood protection from some agricultural areas, the proposed scenarios also show much reduced agricultural damage compared with the baseline.
A sensitivity analysis reported by Evans et al. (2004b), which relates to fluvial and coastal flooding but is based on the same methodology as presented here, indicated that, if the non-structural measures in the Global Sustainability scenario were not implemented and replaced by engineering measures, the cost of engineering works would almost double. This illustrates the amount by which non-structural measures could potentially contribute to reducing flood risk.
Scenarios analysis can form the basis for long-term planning and decision making, for example in relation to coastal management, by illustrating a range of possible futures. Building on the analysis of risks from fluvial and coastal flooding conducted in the Foresight project (Evans et al. 2004a,b), in this paper we have developed scenarios of future coastal flood risk. Socio-economic and climate scenarios have been used in combination in order to generate self-consistent projections of potential future variation in coastal flood risk. In all scenarios the frequency of coastal flooding and associated economic risk is set to increase. The increase is greatest in high-emission scenarios, particularly in the latter half of the twenty-first century. The risk of coastal flooding is strongly modified by societal vulnerability and the scenarios analysis demonstrates how widely that vulnerability may vary according to the trajectory of socio-economic change.
Calculated in real terms, a major driver of increasing flood risk is the increasing value of domestic and commercial buildings and their contents. However, all of this loss may not be perceived to be real, in that damage due to flooding as a proportion of total wealth will grow much more slowly. The extent to which losses are perceived to be harmful will determine willingness to pay to reduce risk through taxation or measures provided by the market (insurance, subscription flood protection, flood proofing, etc.).
In the absence of adaptation, coastal flooding makes an increasing contribution to flood risk from rivers and coasts combined, increasing from roughly 50% in 2002 to 60–70% in the 2080s. This reflects the effect of sea-level rise on the coast and the continuing development of coastal floodplains under some scenarios.
The risk analysis described in this paper has not estimated the risk of loss of life due to flooding. The increasing economic risks in the absence of adaptation are likely to be accompanied by increasing risk of loss of life, though this will be mitigated depending on the effectiveness of flood warning and evacuation measures. The effects of flood damage and disruption to coastal infrastructure such as ports and railway lines are difficult to estimate. However, it is projected that, unless specific measures are taken to reduce the vulnerability of infrastructures, then flood damage will be significant and could impact upon a large proportion of the population, including many who do not live in coastal floodplains.
Potential adaptation to climate and socio-economic change by engineering of flood dikes or retreat from coastal floodplains was implemented spatially in a GIS covering all of England and Wales for four future scenarios. The analysis indicates that engineering works with a one-off capital cost of £12–£40 billion in today's prices could reduce coastal flood risk to a factor of 0.4–1.6 times its current level. Non-structural measures, such as land use planning and flood warning, could also make a considerable contribution to reducing this risk, though no attempt has been made to estimate the cost of these measures.
Analysis of environmental and socio-economic phenomena over a time-scale of 30–100 years in the future involves formidable uncertainties. Changes in some climate variables, for example extreme sea-levels, are particularly difficult to predict. Socio-economic change, which on a global scale leads to changing greenhouse gas emissions trajectories and on the UK scale also determines economic and social vulnerability to flooding, is even more difficult to predict and, it is argued, succumbs only to a scenarios-based approach that can merely illustrate some of the potential range of variation between different futures. Precise results have been quoted for the quantified risk analysis but they should be interpreted merely as providing an indication of the magnitude, rate and spatial distribution of potential change rather than being firm predictions.
Notwithstanding the uncertainties in the analysis, it provides important new insights for policy-makers. ‘Business as usual’ in coastal management over the next century will be accompanied by large increases in flood damage, the magnitude of which will depend on the trajectory of broader socio-economic change. Climate change makes a contribution to this process, but the severity of its impacts is modulated by socio-economic context and the degree of adaptation to change.
Attempts to control the increase in coastal flood risk will need to address these multiple drivers in an integrated manner. There are clear spatial patterns to the distribution of flood risk and the location of its projected increases. Packages of policy response need to be tailored to reflect the characteristics of particular localities. At many coastal sites (including major industrial and infrastructure facilities), there is very limited scope to retreat inland without major economic and/or social implications. The increasing frequency and severity of loading of coastal flood dikes means that they will be increasingly costly to repair or replace. Continued reduction in sediment supply to coasts will be reflected in a narrowing of beaches and deterioration in amenity and ecological value of coasts. Avoidance of these losses requires a long-term strategic approach to coastal zone management.
The research described in this paper was funded by the UK Office of Science and Technology as part of the Foresight Flood and Coastal Defence project. The paper expresses the views of the authors and not the UK Government.
One contribution of 20 to a Theme Issue ‘Sea level science’.
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