Future flood scenarios14 January 2004
Following warnings from the chief scientific advisor to the UK government about the future risks of flooding and a recent conference on the growing threat of floods, it is time flood management rose up the agenda of government policy, says Pete Chan
TIMES are changing in the world of flood management. While the problem of flooding continues to grow, it is becoming increasingly clear that attitudes towards that risk are also changing. Flood management, as we used to know it, is on its way out. Now, flood probability management, flood exposure management and flood resilience management are the latest buzzwords for those in the know.
Crucially, this change in language reflects a fundamental shift in our understanding of the factors affecting flood risk, awareness of which is becoming more and more important as urban development spreads into flood plains around the world.
In the UK for example, where a spate of severe river floods struck in 1998 and 2000, experts at the Office of Science and Technology (OST) have spent over a year working on the Foresight Flood and Coastal Defence project, a scheme under the sponsorship of the government’s Department for Environment, Food and Rural Affairs (DEFRA).
The team has collected data on the factors affecting flood risk – like climate change and the development of land – aiming ‘to produce a challenging and long-term vision for the future of flood and coastal defence that takes account of the many uncertainties, is robust, and can be used as a basis to inform policy and its delivery’.
With this aim in mind, four future flood risk-based scenarios over a 30–100 year timescale have been drawn up and assessed in terms of economic, social and environmental cost.
In an article entitled ‘Climate Change Science: Adapt, Mitigate, or Ignore?’ in the 9 January 2004 issue of Science magazine, David King, the project’s director and chief scientific advisor to the UK government, wrote that sea level rise and increased storminess would let storm surges reach further inland, so that the UK’s coastal defences would be exposed to higher water levels and more energetic wave attack.
The figures reported in King’s article are somewhat alarming. ‘If we assume continuation of existing shoreline management strategies, these combined effects have the potential to increase risk of floods in 2080 by up to 30 times present levels,’ he wrote.
In the most extreme scenario, he continued, flood levels currently expected once in 100 years could be happening as frequently as every three years, and the number of people at ‘high’ risk of flooding in the UK would more than double to nearly 3.5 million.
Among those taking note of the warnings will be Sarah Nason, head of DEFRA’s flood management division. She was one of a series of expert speakers who gave presentations at the ‘Floods: Connecting Communities to Meet a Growing Threat’ conference held towards the end of November 2003 in London, UK.
The British government’s current flood risk management policy, Nason told delegates, includes a range of measures including flood forecasting and warning, flood resilience built into infrastructure, land management and flood defences.
Using figures from the National Assessment of Assets at Risk 2001 and the National Flood Risk Assessment 2003, Nason said England had the equivalent of around US$373B of capital value in areas vulnerable to floods. In the absence of defences, an average of US$5.8B of this would be damaged every year. But with the current range of defences, the actual annual damage is around US$1.7B. These figures, coupled with the fact that some 3.6 million people live in ‘vulnerable’ areas in England might justify increases in future spending on flood defences, said Nason.
Using results from the OST’s Foresight project, Nason pointed out a number of major impacts identified by the work, including precipitation-driven changes in river flood probability and development of land in flood areas. The effects of climate change on flooding, noted Nason, could be unbalanced with river floods becoming more likely in the north and western regions, but lower in the south-east.
Nason outlined DEFRA’s position to over 70 delegates at the conference, which was organised by the National Society for Clean Air and Environmental Protection (NSCA). The conference was NSCA’s first on the topic of flooding, and was held to raise stakeholder understanding amongst those at risk of flood, or involved in defence and mitigation planning. In attendance were a range of representatives from the UK Environment Agency (EA), insurance companies, county councils and action groups.
Nason said it was not yet clear whether the next course of action would be a shift from spending on defences to raising awareness, or a change in the mix of types of defence to achieve the best value for money. But whatever the action taken, she sees flood risk management as a delicate balance between flood probability – a product of climate change and the condition of defences – and flood consequence, which is determined by floodplain development and public awareness.
Similar views were aired by Sarah Lavery of the EA, who spoke about developments along the Thames estuary, in the south-east of England, and the use of the Thames barrier as a risk-based defence. Originally built as a knee-jerk reaction to the floods of 1953, the barrier was approved by legislation in 1972 and became operational in 1982. Since then, said Lavery, it has demonstrated over 20 years of reliable operation, protecting some 1.25 million people and US$145B worth of property value in the flood risk area.
In that time, the barrier has certainly proven its worth, especially in recent years. Referring to data from DEFRA, David King’s article states: ‘usage of the Thames Barrier…has increased from less than once a year in the 1980s to an average of more than six times a year.’ He added that if just one flood broke through the barrier today, it would cost the equivalent of around US$55B in damage to London.
While it would cost over US$3B to build another barrier from scratch to protect the Thames estuary into the future, it would cost only a few million to upgrade the existing structure, making this approach a ‘pretty good investment’, said Lavery. Echoing Nason of DEFRA’s comments about balance, Lavery said: ‘the Thames barrier could have a further 100 years of useful life, but this will be just one element of future flood management.’
With an ageing flood defence infrastructure, and assuming a typical useful life of defences of around 60 years, Lavery said it was important to start thinking about the next generation of defences. But in addition to new infrastructure, other options for dealing with floods included warnings for the public, education programmes and more sensible design and location of buildings, she added.
Lavery summarised the flood risk management plan for the Thames estuary as a combination of strategy (spatial planning and understanding flood risk), asset management (operating, maintaining, improving and extending defences) and flood management (forecasting, emergency responses and event recording).
On top of natural population growth, the problem in the south-east of England is compounded by the fact that large numbers of people are drawn to the area by jobs in and around London. In the period 1991–2001, the population of London grew from around 7 to 7.5 million, according to figures presented by Kevin Reid of the Greater London Authority. Current projections suggest that this figure may top eight million by the year 2016.
While Reid’s figures refer only to London, the implications extend to any region in the world where plans for urban development coincide with flood prone areas. Population growth brings with it extra demand for housing, and if development takes place in the flood plain, there is a corresponding increase in the potential consequences of flooding.
The problem in London, explained Reid, is that virtually all of the city’s boroughs coincide with fluvial flood areas. What is certain to prove a headache for future developers is that many of the poorer areas of London overlap with the flood plain, and that it is these very areas where there are the greatest opportunities for development. This all boils down to flood issues being central to development in many areas of the city, he said.
Future flood risk management may also work at a more fundamental level. In spite of the range of policies, measures and defences in place to protect the population, many people remain oblivious or indifferent to the risks until they are flooded themselves. Both Nason of DEFRA and Lavery of the EA spoke about the importance of raising public awareness to help them to protect themselves against flood risk.
While the NSCA conference was a success and provided a good opportunity for debate, it is not yet clear whether there will be a follow-up event in the future. Certainly, there were plenty of lessons to take away, and given King’s recent warnings, the conference couldn’t have been more timely.
With another team due to report early this year on mitigation measures against the threat of climate change, all eyes now are set on DEFRA, which is to follow up the OST’s research with a new strategy for flood management and coastal protection by the end of 2004. The question is how much of the warnings and recommendations work their way into UK flood management policy.
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