More than 10 million people are thought to be living in homes which are at risk of flooding, according to government figures issued yesterday. The new National Flood Risk Assessment figures now suggest that more than five million homes are at risk, twice the level that was previously estimated.
To make matters worse, the numbers are growing, as climate change increases the incidence of heavy downpours. Londoners are particularly exposed, living in homes exhibiting certain key risk factors. They are living on a flattish landscape, in densely populated areas, and relying on Victorian drainage systems.
What makes the huge difference between the old and the newly published figures is "surface water flooding", the problems that arrive through a combination of heavy rainfall and inadequate drainage. Yesterday's figures include this factor for the first time.
The study of surface water flooding is relatively young, and Dr Justin Butler of flood and environmental consultancy Ambiental thinks that many people will be extremely surprised to find that they are vulnerable.
"We have identified areas at tops of hills that are at risk of surface water flooding," he says. Most of the flooding in London and Hull in the 2007 floods was, in fact, caused by surface water. In short, you could live a long way from a river or the sea and still be susceptible.
We may not know a great deal about surface water flooding, but it is going to be a major subject of discussion over the next few years. At the moment, the Association of British Insurers (ABI) has agreed that its members will continue to provide flooding insurance to most properties, but this promise comes to an end in June 2013, and the ABI says it is not planning to renew it. Homes most at risk of flooding could then find themselves without that part of their household insurance.
Since uninsurable houses become very difficult to sell, those homeowners might lose the possibility of moving home or only be able to sell at very low prices.
The mood music coming from insurers, water companies and the Government is now putting a far greater emphasis on homeowners having to square up to the potential risks themselves.
"It's really about taking personal responsibility for your possessions," says Simon Black, head of flood mapping at insurer Norwich Union. "If I lived in a high-risk area, I would be doing as much as possible to reduce my own risk. And I would always, whenever moving, look to see if the house was at risk of flooding."
And Richard Aylard, director of sustainability at Thames Water, says: "Homeowners can do an awful lot to help themselves by being very careful about what they put down the drain."
The water company says that more than 80 per cent of drain blockages, a major contributor to surface water flooding, can partly be blamed on people putting inappropriate material down sinks and toilets – such as fat used in cooking, or cotton buds.
The truth is that we do not know yet how much damage surface water flooding might cause, although most experts believe it could be both a substantial and a growing problem.
"Modelling river flooding is a pretty advanced science," says Simon Black. "Modelling surface water has just passed its embryonic stage."
Malcolm Tarling of the ABI says: "We first voiced concern about lack of drainage following the 2007 floods." Surface water was involved in two-thirds of the 55,000 properties flooded in 2007.
Ambiental is one of the leading scientific companies in the field, and has produced surface water maps that it is now consulting on with other experts. This type of three-dimensional map will come to be widely used across the insurance industry in the next couple of years. "Insurers are becoming much more savvy about this," says Dr Butler. They are far more likely, he says, to ask homebuyers in risk areas to get an individual flood risk assessment report on their home when applying for cover.
Behind the scenes, the Government is becoming much more focused on flooding issues in general, and surface water flooding issues in particular.
The Environment Agency is being given lead responsibility for the problem, with new overview powers being assigned to it in the draft Flood and Water Management Bill. The Agency also opened a new Flood Forecasting Centre in April, which is working on producing surface water maps that it will make available to the public when they are ready, perhaps in a year or two.
The Environment Agency is going to have to deal with some highly delicate issues. Much of the work we have done to erect barriers against river flooding has, in fact, made us more vulnerable to surface water flooding.
Kew is one of the worst potential problem spots in London, according to Ambiental, partly because the river Thames' flood defences stop heavy rainfall draining away into the river.
Local authorities will need to crack down much harder on risky developments. About 4 per cent of large developments, including schools and homes, are still being constructed in flood plains and against Environment Agency advice.
Another mistake we have made in the past is the concreting-over of our cities, leaving fewer natural drainage routes for heavy rainfall. But planning authorities are becoming tougher on this. "It will be much more difficult to tarmac over in future," says Dr Butler.
There is also no question that it is the public that are going to have to pay more to replace their ageing drainage and sewerage system. Thames Water has just put in the biggest investment request ever to the regulators: a £5.5bn proposal.
This would see water bills go up 17 per cent by 2015, to an average of £331 per household. This might seem a lot, but the alternative is not pretty. The worst form of surface water flooding comes when sewers become blocked and then flood.
Thames Water's long-term investment programme aspires to end the risk of sewer flooding from all buildings in its area, but this will still take until 2035 to achieve.
Stay protected: Reduce the risk of flooding
* Find out if you are at risk. Ambiental (www.ambiental.co.uk) and other flood consultancies provide maps and advice on all flood risks. The Environment Agency is moving towards surface water maps, but already provides river and coastal flooding maps as well as general advice. Ring 0845 988 1188 or go online at www.environment-agency.gov.uk.
* Work with neighbours. Lobby your local authority (if you are in a danger zone) and check the drains in your street. Even clearing away leaves from drains can help considerably.
* Observe your own house. When it rains, see where puddles develop. Micro-solutions in your own property can stave off problems. Ensure there are channels for water to escape in and do not concrete over all your garden.
* Recognise potential problem areas. Basements are particularly prone to flooding. The flat lands of much of the Thames area drain more slowly than the uplands of, say, Birmingham. The clay subsoil of much of the Thames area is also far less absorbent of water than the chalk areas of parts of Kent.
* Be prepared. Calculate as precisely as you can the exact risk facing you (whether river or surface water, for instance), the defences in place in your area and then the steps you need to take. Raising door thresholds, building flood-resistant walls and reshaping driveways are three possibilities suggested by the Environment Agency. If flooding looks likely, then minimise the damage by, for example, raising electrical sockets from floor to eye level. Read the Agency's website for other practical suggestions.
A rising problem? Flood timeline
The wettest autumn since records began in 1766 puts flooding issue on political agenda. 10,000 properties flooded.
A Foresight report, commissioned by the Government, concludes that annual flood costs, then £1bn, could soar to £25bn per year in a worst-case scenario by the end of the century. (Subsequent climate change research suggests the problem is greater, although it is still impossible to be precise.)
Flooding hits the UK in June and July affecting 48,000 homes and 7,000 businesses at an insurance cost of £3bn, making it "the most costly insured weather event in the UK", according to the Association of British Insurers. Over 63 per cent of the flooding in England and Wales is caused by surface water.
Environment Agency opens the Flood Forecasting Centre and gets greater management and co-ordination powers. Thames Water puts in a £5.5bn request to regulators for 2010-15 to fund an investment programme, the biggest ever by any water company in the UK. Regulator Ofwat's response in July will indicate whether the Government and regulators accept the argument for rebuilding much of the water and sewerage infrastructure.