Focus: They are the kind of floods that hit twice a century - but they have come twice this summer already. Some of England's biggest rivers were still rising last night, swollen by record rainfall.

They are the kind of floods that hit twice a century - but they have come twice this summer already. Some of England's biggest rivers were still rising last night, swollen by record rainfall.

Scientists used to expect such events once every 50 years. Now they are thinking again, thanks to global warming.

This week some of the world's top climate experts will warn that a warmer world will have more extreme weather. A new report, to be published in the science journal Nature, predicts more severe rain across temperate areas, including the British Isles.

"In the UK wetter winters are expected which will lead to more extreme rainfall, whereas summers are expected to get drier," said Peter Stott of Reading University, one of the report's authors. "However, it is possible under climate change that there could be an increase of extreme rainfall even under general drying."

So, countries such as Britain could be drier, but face more flooding. And that will mean dramatic changes in the way homes, businesses and roads are planned. The flooding in England this week - or the crisis in Yorkshire earlier this summer - may or may not be a symptom of global warming. No scientist would draw conclusions from a single event. But the trend is clear. Even the insurers, facing a bill of £2bn of UK flood damage from June and July, agree.

Swiss Re, one of the biggest underwriters of insurance in the world, reckons floods are now killing 7000 people a year, roughly a third of all victims of natural catastrophes such as storms, earthquakes, droughts and extreme cold or heat.

Statistics gathered by insurers - who look at the cost of a catastrophe to measure its severity, not the death toll - also indicate climate is changing.

"One single event can never be a sign of climate change," said Jens Mehlhorn, who heads a team of flood experts at the Zurich-based company. "But when you see a series of such events, and that's what it looks like at the moment . . . it may be about time to say something is changing."

This year's UK floods were an event statistical models say should happen once only every 30 to 50 years, Mr Mehlhorn says: yet floods were also seen in 2000.

Two such events in only seven years are not statistically impossible, he said. But they are unlikely. Other countries have had similar increases in such disasters.

The 2000 floods sparked the same concerns over global warming as last weekend's. John Prescott, then in charge of the environment as deputy prime minister, said they were a "wake-up call".

A panel of experts, the Flood Commission, was set up under the chairmanship of a Strathclyde University engineering professor, George Fleming. Among scores of recommendations, it said flood defences should be tough enough to endure a "one-in-200-year event". The Scottish Executive, memories of the 1995 flooding in Perth still fresh, agreed. Authorities in England were less enthusiastic. Minds, however, are now being focused south of the border.

"They are going in that direction now," Prof Fleming said last night. "I am sure that the current crisis will accelerate work. But it's a massive job, similar to upgrading all our roads and railways to new standards."

Scotland, of course, doesn't have the kind of river systems seen in England or on the continent - although Prof Fleming is quick to point out that the Tay carries more water than the Severn and Thames put together. Scottish councils have also made it much harder to build on flood plains than those south of the border. But none of the experts is being complacent.

Paul Jowitt, a civil engineering professor at Heriot-Watt University, said: "We may not see the scale of flooding they have in England but it would be unwise to assume we would not see it here."

Scotland, for example, would be far from immune to the localised flash-flooding that hit Sheffield this summer or the east end of Glasgow four years ago.

The Scottish Executive says it is well aware of the threat. A spokeswoman said: "Increased risk of flooding is one of the ways in which climate change will affect Scotland, but the legislation that deals with flood alleviation is inadequate and needs to be updated. We therefore recently announced that flood risk management will be consulted on, with a view to legislation."

Scotland, like England, is embarking on massive housebuilding. Developers and their insurers are starting to wise up to the risks of building houses near rivers. The more land is built on, the less land there is to soak up rain. Even paving over gardens to make driveways can contribute to local flooding.

Officials desperate to see more homes built - not least to take pressure off house price inflation - yesterday tried to talk down the threat of flooding.

UK Housing Minister Yvette Cooper warned that the floods should not be used as an excuse to "whip up hostility" to new housebuilding. She said critics should not "play politics" with the floods to block urgently needed new developments to provide affordable homes.

The Westminster government's housing green paper - to be published later today - is expected to warn that it is "unrealistic" to prevent building on flood plains. Engineers such as Prof Fleming are not so sure that's a good idea. Professor Bill McGuire, director of Benfield UCL Hazard Research Centre, said: "While it still holds true that we can never attribute a particular weather event to climate change, the current devastating floods form part of an expected trend that will see the country facing more frequent and bigger floods in coming decades.

"We need to be aware that anywhere on a flood plain could flood at any time, and take remedial action now. Any plans to build properties on flood plains, given climate change predictions and recent events, would be irresponsible in the extreme."

Nick Reeves, executive director of the Chartered Institution of Water and Environmental Management, agreed. "Scratch the surface of flooding-related problems and it comes back to the way we live our lives," he said.

He said the time had come to manage demand for new homes. "The government must learn the lessons of these floods and avoid storing up problems for the future by concentrating on development on brownfield sites.

"They need to undertake a strategic land review, as less than 1% of the population of Britain owns 70% of all land. The condition and status of much of this land is unknown and it may be that some of it could be released for housing."

Plugging the gaps

Millions of pounds are currently being spent to shore up flood defences across Scotland.

The Scottish Executive covers four-fifths of the cost of all projects.

Projects include:

• White Cart
  Glasgow and Renfrewshire.

A £50m project to shore up defences along around six miles of the river, including "hard" walls and new areas set aside for nature flooding.

• Braid Burn, Edinburgh
  Estimated total cost £28.5m over 2007-11.

The Edinburgh burn burst its banks in 2000. The new scheme will protect properties between Redford Road and Portobello.

• Dunfermline
  Estimated cost £11.15m from 2007-10. It is a new scheme to protect 175 homes in areas such as Lyne Burn, which has long suffered flooding.