SEVERE floods on a scale previously seen once every century could strike England and Wales every three years by 2080, a government study of the impact of global warming says.

London, the Solent, north Norfolk and other coastal areas will become 30 times more vulnerable to devastating wave surges, raising the annual economic costs of flooding from £1 billion to more than £20 billion, according to scientists’ worst-case scenario.

The danger of flooding from swollen rivers and more intense and frequent storms will rise by between four and six times, and the number of people whose homes are at high risk will more than double to 3.46 million.

Even under the most positive scenario, in which the world takes substantial steps to hold back climate change, the impact on Britain will be great. The flood risk will rise by at least 30 per cent around the Thames and Severn estuaries, the Wash, Portsmouth and the Sussex coast, and the annual cost of flooding will reach £4.8 billion, with 2.4 million people in high risk flood plains.

The bleak picture has emerged from the Foresight Flood and Coastal Defence Project, a £1 million study involving 40 researchers and the most sophisticated computer models of the British climate and coastline ever developed.

The project, run by the Government’s Office of Science and Technology, is the first of its kind in the world. While previous models have predicted temperature and sea-level change, Foresight also uses input from economists and sociologists to build a much more complete picture of the long-term effects of global warming.

Its first results, seen exclusively by The Times, chart the impact of changing weather patterns and sea levels over the next 100 years under four scenarios of economic growth and international environmental policies. All assume that Britain’s existing approach to flood management remains unchanged, and the next stage of the scheme will recommend how this should be revised to limit the effects.

The worst case is the “World Markets” scenario, in which global free trade brings fast economic growth, but little is done to address the threat of global warming. The most favourable is “Global Responsibility”, which also includes relatively high growth, but assumes successful international co-operation to cut greenhouse gas emissions.

Sir David King, the Government’s Chief Scientific Adviser, who is overseeing the Foresight project, said that the results demonstrated an urgent need to tackle global warming and deal with effects that will be felt even if the Kyoto Protocol on limiting greenhouse emissions and subsequent treaties are successful.

“The flood risk to homes in the UK has increased significantly, and we’re saying this is going to continue into the future,” he said. “In the World Markets situation, in some areas of the country the risk of severe flooding, which was one in 100 years, will rise to one in three years by 2080. In others it will be one in seven, or one in 15, but there are no areas in which it doesn’t get worse.

“Even in the best case, the map is still covered in areas of dark red, indicating a high increase in risk.

“It highlights the importance of global action on mitigation of climate change. It is so obvious which of these scenarios you want to be in on. We’re not in the business of scaring people, but this is the best prediction of what scientists and economists can currently say about coastal defence and flood risk. It’s a story that says action is required. No action is going to bring the greatest economic cost to this country.”

The effects of sea level rise are already with us, Sir David said. “When the Thames Barrier was opened in 1982, it was closed three times in its first five years, in line with its predicted usage,” he said. In 2001 it was closed 14 times, each of which would have cost London about £30 billion if it hadn’t been there.”

Increased rainfall, particularly in winter, is another predicted effect of global warming that will further increase pressure on flood defences.

Britain is forecast to warm by as much as 5C (9F) by 2080, bringing more rain, fiercer storms and swollen rivers. Under the World Markets scenario, the worst affected areas would be East London, the Thames estuary, north Norfolk, the Solent and the Sussex coast. Other estuaries, including the Severn and the Humber, will also be badly hit.

Virtually the entire West Country, encompassing most of England to the west of a line drawn from Southampton to Gloucester, will be at significantly increased risk by 2080. The outlook is also poor for parts of the Pennines, Cumbria and Lincolnshire.

The Foresight findings will be formally published at a special conference on July 7, and the team will start examining potential strategies for adapting to climate change and limiting the risks.

This will involve a combination of stronger flood defences, tighter planning regulations on building in flood plains and abandoning to the sea tracts of land that are too expensive to protect.

The scenarios do not cover Scotland and Northern Ireland, which are outside the authority of the Whitehall departments handling the scheme. The risks from flooding in both countries, however, are lower than in England and Wales.

The country’s stormy past

2000, autumn: Wettest since records began in 1766, flooding 8,000 properties in Sussex and Kent

January 2003: Thames Barrier closed 14 times, more than double the previous record in October 2000

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