The Big Question: Is flooding really as big a risk to Britain now as terrorism?

Why are we asking this now?

Because yesterday, Sir Michael Pitt published his long-awaited report on last year's disastrous summer flooding in Yorkshire and the Severn valley around Gloucester and Tewkesbury, which caused the largest peacetime emergency in Britain since the Second World War. It said that the importance of flood risk should be "brought up alongside the risk of terrorism or a major flu pandemic". To emphasis this, there should be a government cabinet committee concerned solely with flooding, he said.

That's a bit strong, isn't it? What were his reasons?

Related articles

• MI5: revealing areas at mercy of collapsing dams is a terror threat
• Search the news archive for more stories

The main one: floods hit much more than just houses. In studying them, Sir Michael, an engineer and former local authority chief executive, was struck by just how quickly major parts of Britain's infrastructure, such as water-pumping stations, electricity sub-stations and the transport networks could be, and were, overwhelmed and knocked out by the floodwaters.

There was a "quite extraordinary chain reaction" he said, from what started off as a straightforward flooding emergency – bad enough in itself – into something hitting many thousands more people than those actually affected by the rising waters.

For example, although 55,000 properties were flooded over the course of the summer, and about 7,000 people had to be rescued by the emergency services, once infrastructure was hit, the numbers shot up. The flooding of the Mythe water treatment works in Gloucestershire, for example, left 350,000 people without mains water supply for up to 17 days. When the Castle Meads electricity sub-station was shut down, 42,000 people were left without power in Gloucester for up to 24 hours. Some 10,000 people were trapped overnight on the M1. Five-hundred people were stranded one night on Gloucester railway station.

And as we report elsewhere, if the Ulley reservoir dam near Rotherham had burst – and it very nearly did – something like a million people might have been without any power in the Sheffield area, a quite unprecedented situation in Britain. You would have to admit that a terrorist outrage which did that would be regarded by its perpetrators as a success.

But terrorism is a continuing threat. Weren't these floods a one-off?

Yes and no. There has certainly been nothing like the rainfall of last summer, at least in the rainfall records which go back to 1766. June, July and August, taken together, made the wettest summer we have ever seen, and the two critical downpours, which hit Yorkshire from Hull to Doncaster on 24 June, and the area of the Severn valley on 19 July, were probably as heavy as anything Britain has experienced. The trouble is – there are likely to be more of them.

Why is that?

Because of climate change. Sir Michael said yesterday that one of the most frequently asked questions during his review was whether climate change was directly responsible for last year's flooding episodes – and the answer was, it was impossible to say with certainty.

However, new research, commissioned for his report, indicates that there is an even bigger likelihood of such "extreme rainfall events" in the future, because of global warming, than was assumed until quite recently. In 2004, the Government published the Foresight Future Flooding report, which sounded the alarm about the heavier rainfall expected in a warmer atmosphere over a 30-100-year timescale. The Foresight conclusions were reassessed for the Pitt Review and they are now gloomier (or should that be wetter?) still.

For example, in the worst-case scenario, total winter precipitation increases by 40 per cent over the coming decades, as opposed to 25 per cent in the 2004 projections. The possibility of dangerous sea level rise is also seen as more likely than in the earlier report.

So what can we do?

A great deal, and we need to get on with it, says Sir Michael, who makes 92 recommendations for action, and says they should be carried out within two years. In general terms, we need to boost the flood-warning system; improve the building regulations; get the bureaucracy right (we need to establish a national flood warning centre staffed by the Environment Agency and the Met Office); make sure the water rescue system is coordinated nationally; and make sure all advice is consistent. And above all, we need to learn to protect critical infrastructure sites and make sure that the authorities are informed on the implications of them being knocked out.

And is this to cost billions?

Sir Michael says 80 per cent of it can be done out of existing budgets. It's not so much building new defences, more a question of thinking about the risks in a different way. For example, the 2007 floods threw up what was really a new flooding problem – the effect of surface water. In the past, major floods have been caused by rivers overflowing, or, occasionally, by the sea invading the land (as in the catastrophic floods of January 1953, in which 307 people drowned).

But although the July floods came from rivers – Tewkesbury, which was cut off, is where the Avon meets the Severn, and thus suffered a double whammy – the very damaging flooding in Hull and Doncaster last June was caused by something else entirely – the local drainage systems being unable to cope with the volume of rainwater pouring into them. This was such an unpredicted risk that no national authority had responsibility for it – as the Environment Agency has long had responsibility for river and sea flooding.

Now the agency is taking the surface-water problem under its wing, and local authorities, Sir Michael says, should have a duty to map all their drainage systems, and work out who owns them, who's responsible for maintenance, and which places are likely to flood.

Can we do anything about surface water flooding?

Besides improving the municipal drains? Yes, we can stop concreting over our front and back gardens, which decreases the permeability of the land. Sir Michael would like that made subject to planning permission.

And we can make sure housing developers think about drainage first, instead of last (as Sir Michael alleges they do at the moment). There are very clever modern drainage systems which can get rid of surface water very effectively. Clever, in fact, is what we will need to be to adapt effectively to the soggy future that seems to be awaiting us.

Might flooding prove as big a problem as terrorism?

Yes...

* Flooding can knock out key infrastructure just as effectively as a terrorist bomb

* Flooding is gaining an intensity we have not experienced before

* Flooding will continue to get even worse

No...

* Terrorism can take many more forms, from assassinations to bombings

* Flooding is generally restricted to flood-vulnerable areas – terrorism can get anywhere

* In theory, terrorists could inflict devastation beyond any flood, with a nuclear device

Switch your Gas & Electricity and save up to £380 with Independent Compare