Article - Issue 21, November/December 2004
A new climate for flood planning
Professor Edward Evans Visiting Professor, Glasgow University Professor Jim Hall Professor of Earth Systems Engineering, University Of Newcastle
One consequence of climate change for the UK could be an increase in flood risk – a combination of the frequency of flooding and its economic impact. The Foresight Flood and Coastal Defence Project brought engineers together with other experts to assess the likely changes in flood risk over the coming century and to evaluate possible responses.
For centuries Britain has relied upon engineering for flood protection. Sea defences, raised river banks, land drainage systems and widened and straightened rivers have generally been successful in protecting individuals and property from flooding due to rainfall and extreme coastal events. In the UK, the Thames Barrier is perhaps the ultimate, and most expensive, example of the engineered approach to flood defences. These responses to flood risk have developed thanks to improved technical understanding and have been shaped by changing economic priorities and environmental pressures.
Erosion and land movement are constant pressures on the UK’s shoreline. Human activity, such as land drainage for agriculture or the development of flood plains for housing, adds to this burden.
A new factor has entered the picture in recent years, prompting the Government's Chief Scientific Advisor, Professor Sir David King, to initiate the Foresight Flood and Coastal Defence (FCD) Project within the Office of Science and Technology. Professor King was concerned that climate change, accelerated by anthropogenic releases of carbon dioxide into the atmosphere, would create new challenges for the UK.
The FCD project ran from October 2002 to April 2004. It involved more than 60 experts from many disciplines. The project was one of the most extensive investigations ever undertaken of a nation’s exposure to flood risks, a combination of the frequency of flooding and its economic impact.
Input came from experts from industry, government and academia in, among other disciplines, climate science, geography, hydrology, engineering, social sciences, sewerage, agro-economics, urban and rural ecology, coastal erosion, water management and risk analysis. The project enabled a constant interaction between these disciplines, with, for example, specialists in environmental science assessing engineering responses to increased flood risk. For their part, engineers advised on the possibility, cost and effectiveness of different responses to particular threats. Our final report details three key reasons for embarking on this important study:
While engineering will remain at the heart of flood-risk management, on its own it cannot combat the rising risks from climate change and socioeconomic change. Instead we propose balanced portfolios of structural and non-structural policies to achieve a sustainable future for flood-risk management.
There is considerable inertia in the built environment. It could take decades for changes in planning and building regulations to take effect if we want to alter land use or to increase the resistance of buildings to flooding.
Reducing global emissions of greenhouse gases could play an important role in mitigating flood risk in the second half of the century. However, the time delay inherent in the atmosphere and oceans means that action needs to be taken now to achieve that.
The cost of flooding
Flood damage and flood management are estimated to already cost the UK some £2 billion a year on average (see box). Such is the rise in property values, and the cost of the consumer goods with which we surround ourselves, that this bill would continue to rise even if the extent of flooding – the number of properties or the land area inundated – remained unchanged. However, models of future flooding based on national and international scenarios of climate change suggest that the frequency of flooding will increase under all scenarios.
Thanks to the FCD project, we now have a detailed and much better idea of how the pattern of flooding might change, and of the potential economic and social impacts of that flooding. The research did not set out to predict how many properties or how much land will succumb to flooding and altered patterns of rainfall as the result of climate change. Instead, we analysed the increase in flood risk, expressed as the product of probability times consequences. Expressed in this way, flood risk can rise even if there is no increase in flooding, simply because homes, their contents, and industries will become more valuable. Building contents are also becoming more vulnerable to flood damage, for example because of the proliferation of electronic equipment.
To assess the possible increase in flood risk to the end of the century, the FCD project made use of a series of scenarios of possible socio-economic and environmental futures. Economic development and the future climate are clearly closely related. For example, economic growth is a driver of energy use and emissions of greenhouse gases.
There are many possible combinations of socioeconomic and climate scenarios. The five we chose allowed us to investigate a wide range of possible futures. Our four basic scenarios – the Foresight Futures – embody different approaches to governance (centralised versus localised) and different values held by society (consumerist versus community) (see Figure 1). We also associated each socioeconomic future with a different scenario for climate change. For example, a socioeconomic scenario of high growth (termed ‘World Markets’) is matched with high emissions of greenhouse gases (see Figure 1). In addition, we tested a fifth scenario in which a high growth ‘World Markets’ economy managed to achieve low emissions of greenhouse gases.
The FCD project differed from many earlier assessments by deploying a quantitative assessment methodology known as RASP (Risk Assessment for Strategic Planning) to explore future flood risk and the responses that society might use to reduce the expected increase in that risk. The RASP methodology, developed with funding from the Department for Environment Food and Rural Affairs (Defra) and the Environment Agency, uses national databases of the location of river and coastal flood plains, the economic assets at risk from flooding and the standard and condition of flood defences. From this information the RASP methodology estimated the probability distributions of the depth of flooding which, when combined with census data and commercial databases of the location of property and population, allowed us to estimate the economic risk from flooding. The analysis therefore provides:
An estimate of the flood risk associated with the failure of any flood defences, either alone or in combination.
An estimate of the total flood risk for identified impact zones in the flood plain.
An indication of the contribution that each defence makes to the total risk in the flood plain.
A picture of flood risk mapped onto a 10 km grid for the whole of England and Wales, showing people at high risk, economic damage to both property and agriculture, and a social vulnerability index giving an indication of how flooding might affect different parts of our society.
Total figures for economic damage and people at high risk for England and Wales.
The project considered flooding in terms of a series of ‘drivers’ (see Table 1). A driver is any phenomenon that may change the state of the flooding system. A driver can operate at a level where we have no control – for example, solar activity and the Earth’s orbit (see Figure 2). Other drivers, such as emissions of greenhouse gases leading to climate change, operate at a global level and, while controllable in theory, are difficult to influence at a local level and even nationally, depending instead on international accords. Some drivers of increased flood risk, such as flood defences and flood forecasting and warning, are under the control of flood managers, locally and nationally.
Having reviewed the potential drivers of increased flood risk, the project then went on to assess possible responses to changes in flood risk that arise from those drivers.
We first identified the responses through a process of review and consultation. We then evaluated the responses against six simple metrics of sustainability: reduction of flood risk, cost effectiveness, environmental quality, social justice, precaution and robustness.
Responses can operate at different levels; from global agreements to limit emissions of greenhouse gases, through national and local schemes to deliver flood warnings or to prevent development of flood plains, through to actions by individuals, such as moving vulnerable economic activities and infrastructures out of reach of rising flood water.
Drivers that are under the control of flood managers can also operate as potential ‘responses’ to flood risk. It is also possible, in certain circumstances, for responses to become drivers. For example, engineering to control flooding in a town will affect flooding downstream and will therefore be a driver of downstream flood risk.
Our analysis combines the concepts of drivers and responses with the Source-Pathway-Receptor (SPR) model for risk assessment. This characterises the flooding system in terms of flooding sources, pathways and receptors or a combination of these.
The SPR model provides a well-established framework for environmental risk assessment. In the case of flooding:
Sources are weather events, or sequences of events that may result in flooding (e.g. heavy or sustained rainfall and marine storms).
Pathways are the mechanisms that convey flood waters that originate as weather events to places where they may impact on receptors. Pathways therefore include fluvial flows in or out of river channels, overland urban flows, coastal processes and failure of fluvial- and sea-defence structures or urban drainage systems.
Receptors are the people, industries and built and natural environments that flooding affects.
Through literature review and consultation with a wide range of experts and stakeholders we generated a comprehensive list of around 80 possible responses to future flood risk. We then grouped related responses into a series of 26 groups within five broad themes (see Table 2): Managing the Rural Landscape; Managing the Urban Fabric; Managing Flood Events; Managing Flood Losses; and River and Coastal Engineering and Realignment. We also identified possible responses in urban areas and considered these in a series of themes: Building Development Operation and Form; Urban Area Development; Source Control; Groundwater Control; Storage Above and Below Ground; and Main Drainage Operation and Form. (We describe these responses in great detail in the technical reports referred to in the Further Reading section.)
Most responses to flood risk aim to modify the pathways or receptors of flooding. However, we also considered the possibility of reducing flood risk by decoupling socioeconomic growth from increased emissions of greenhouse gases.
The project constructed integrated portfolios of responses, one for each of the four future scenarios and assessed its ability to reduce flood risk in the 2080s. The content of each portfolio depended on the nature of the scenario in question.
Summary and conclusions
An important message from our analysis is that engineering alone cannot accommodate the increasing threat that flooding poses to economic and social activity in the UK. We can greatly reduce risks by implementing a portfolio of responses. We found that if we used engineering alone to manage the additional risks, it could cost £52 billion of investment. This compares with £22 billion when using engineering in concert with a range of non-engineering measures.
Under every scenario, our analysis suggests that if current flood-management policies remain unchanged, the risk of flooding and coastal erosion will increase greatly over the next 30 to 100 years. However, another important conclusion is that in most scenarios the benefits of implementing risk reduction measures clearly exceed the costs.
While our analysis confirms that engineering solutions alone cannot reduce flood risks to acceptable levels, we should emphasise that in all of the future worlds we analysed we would need engineering responses to meet the increased flood risk. However, we can increase the sustainability of our management policies by implementing a portfolio of responses. The key message is that it is how the responses are implemented, rather than the responses themselves, that is at issue.
Thanks to the FCD project, we now have a detailed and much better idea of how the pattern of flooding might change.
We found that if we used engineering alone to manage the additional risks, it could cost £52 billion of investment. This compares with £22 billion when using engineering in concert with a range of non-engineering measures.
Exposure to flood risk
Nearly 2 million properties in flood plains along rivers, estuaries and coasts in the UK are potentially at risk of river or coastal flooding. Eighty thousand properties are at risk in towns and cities from flooding caused by heavy downpours that overwhelm urban drains – so-called ‘intra-urban’ flooding. In England and Wales alone, over 4 million people and properties valued at over £200 billion are at risk. The UK government currently invests around £500 million per year on flood management.
A decade of Foresight
The Foresight Flood and Coastal Defence Project was the first of a new phase of the Foresight Programme of the Office of Science and Technology. As such, along with the Foresight Cognitive Systems Project, it was a test-bed for a new type of project.
Earlier phases had wider remits and more general objectives. The projects, mostly linked to sectors of industry, considered broad areas of science and technology, dealing with such issues as Agriculture, Natural Resources & Environment, Chemicals, Financial Services, Materials and Transport and many other topics. A major objective was to bring together industrialists, scientists, engineers and Government, with a focus on promoting wealth creation and quality of life.
Much has changed in science, engineering and technology in the past decade. Thanks in part to the work of Foresight, there are now much closer links between academic researchers and industry.
In Foresight’s third phase, launched in April 2002, the starting point for a project is either: a key issue where science holds the promise of solutions, or an area of science where the potential applications and technologies have yet to be-considered and articulated.
Full reports of the Foresight Flood and Coastal Defence Project are available on the Foresight website, along with the report Foresight Futures 2020: Revised Scenarios and Guidance, www.foresight.gov.uk, Office of Science and Technology (2002), Office of Science and Technology, London.
Further details of the UK Government’s spending on flood protection are on the website of the Department for Environment Food and Rural Affairs www.defra.gov.uk/environ/fcd/policy/funding.htm
The project also supported development of FloodRanger, a flood simulator (a kind of flooding SimCity) that puts the player in control of a piece of UK coastline.
Guidelines for environmental risk assessment and management, DETR, Environment Agency, Institute for Environment and Health, 2000. www.defra.gov.uk/environment/risk/eramguide/
Hall, JW, Dawson, RJ, Sayers, PB, Rosu, C, Chatterton, JB and Deakin, R, ‘A methodology for national-scale flood risk assessment’, Water and Maritime Engineering, Volume 156, pp 235–247.
RASP Project: http://www.rasp-project.net/
Visiting Professor, Glasgow University
Professor of Earth Systems Engineering, University of Newcastle
Edward Evans is a Visiting Professor at Glasgow University. He was formerly head of Halcrow Group Ltd’s Water Resources department, and was the originator of the ISIS suite of river modelling programs which are widely used in the UK and all over the world. He was recently Lead Technical Advisor for the OST Foresight Future Flooding project and manages the Broad Scale Modelling research programme for Defra.
Professor Jim Hall has recently been appointed to the Chair in Earth Systems Engineering at the University of Newcastle-upon-Tyne. He was formerly a Royal Academy of Engineering postdoctoral research fellow at the University of Bristol where he researched new methods of risk and uncertainty analysis for flooding and coastal systems. He was Principal Investigator of FloodRiskNet, the EPSRC’s Flood and Coastal Risk, Reliability and Uncertainty Network.