martes, 24 de julio de 2007

Flooding in England: What can be done?

New Scientist Environment Blog.
Tuesday, July 24, 2007
Here in England, the media is awash with reports on the recent flooding, which has made what was just a gloomy summer a whole lot worse for many thousands of people. Think houses under 3 feet of sewage-infected floodwater.

The floods came just as a study revealed the first firm evidence for the hand of global warming in changing rainfall patterns. By definition, no single weather event can be attributed to climate change. But there's widespread agreement that at the mid-latitudes where England sits, it's going to get wetter on average – a warmer world means more evaporation. It's also thought the intensity of storms will increase.

But back to the English floods. The Science Media Centre in London rounded up some interesting points of view. First, the floods were pretty exceptional.

Very unusual weather conditions across much of the UK have persisted throughout the summer of 2007, leading to the highest May and June combined rainfall total on record. It is unusual for soils to be close to saturation point at this time of year, and this in combination with several days of intense rainfall has lead to flooding that has no close modern parallel.

Barnaby Smith, Centre for Ecology and Hydrology

They were also unusual in where they started:

These floods are very unusual – "mid-catchment" floods, meaning heavy rain falling, not in the uplands, as is normal, but in the middle parts of river basins.

Stuart Lane, Institute of Hazard and Risk, Durham University

But there have been more extreme local events in the past:

The rainfall events on 20 July were unusual in that the cloud system remained nearly stationary for a considerable length of time, resulting in about 100 millimetre rainfall depths.

But similar levels of heavy localised rainfall have occurred during the past hundred years. For example:
- 110 mm in an hour near Oxford in 1910
- 140 mm in 2 hours at Hampstead, London in 1975
- 178 mm in 3 hours in Lincolnshire in 1960
- 200 mm in 8 hours in Somerset in 1917

Alastair Borthwick, Professor of Engineering Science, University of Oxford

Here's a montage of the flooding from YouTube:

With the UK government announcing on Monday plans for millions of new houses, there has been much talk about the wisdom or otherwise of building on flood plains. Flood plains are flat and conveniently located for many urban areas – but they are flood plains, which come under water when rivers periodically break their banks. But this point is interesting:

Ten per cent of UK housing is on flood plains, but this is quite low compared to some countries – it is 70% in Japan and 100% in the Netherlands. We need better flood defences.

Ian Cluckie, Professor of Hydrology and Water Management, University of Bristol

That has been a common refrain – you'll never stop all floods. All you can aim for is to reduce the risk of them, and cope better when they happen. So how do you do that? One big issue is run-off.

When rain falls, the ground can soak up some of it, meaning it does not run into rivers and raise their level. But the harder the rain falls, the more runs off, and the less soaks in – and rainstorms are predicted to get more intense as the planet warms. The other key issue here is urbanisation – water rolls off concrete and straight into drainage channels – and that will increase with the plan to build millions of new homes.

There's a clear irony about the floods, given that in the summer of 2006 in England, all the talk was of droughts and hosepipe bans.

What is significant and thought provoking is that a year ago we were seeking ways to retain water. Now we are desperate for it to go out to the sea. What we need is a more holistic approach that recognises the role of catchments in terms of flood storage.

Justin Taberham, Director of Policy, Chartered Institution of Water and Environmental Management

Here's a picture of that holistic approach:

You cannot design flooding out of urban spaces. Therefore it is vital that planners and developers move away from trying to resist seasonal influxes of water [which are increasing in volume] and move towards designing for flooding and absorbing excess water safely. This can be aided by taking some simple steps such as: incorporating green roofs, creating recreational areas within cities, and providing storage areas such as wetland habitats and water bodies upstream. In fact, planners could take this as a golden opportunity to make properties safer, but also improve our environment with green spaces and create richer habitats for wildlife

Bob Sargent, President, Chartered Institution of Water and Environmental Management

It's either that or building houses on stilts, I'd say.

Talking of holistic, it turns out that the responsibility for the various aspects of drainage appears oddly disparate: road drainage, surface waters, sewage drainage and flood protection are the separate responsibilities of local councils, the Environment Agency and water companies. Not very joined up. What are often joined up, but shouldn’t be, are surface drainage channels and sewage drainage, making a real mess when floods happen.

So are there any silver linings? Not many. The risk of disease following the floods is low:

Despite the dire warnings about outbreaks of disease following flooding, they rarely happen.

Keith Jones, Health-Related Environmental Microbiologist, Lancaster University

And the wet weather could break at any time:

There's no obvious culprit for the unusually long wet spell we've been experiencing this summer and so there's no reason to believe it will persist for the rest of the summer. We could revert to more normal summer weather at any time.

David Stephenson, Met Office Chair, University of Exeter

Now if anyone knows what is "normal weather" for the famously capricious English summer, do let me know.

More seriously, I'd love to hear what you think should be in done in the aftermath of this flooding – bigger defences, a ban on flood-plain building, the "holistic" approach above, or is it the houses on stilts, or even house boats? Lastly, if you have been affected by flooding, do share your experiences.

Damian Carrington, online editor
(Image of Tewkesbury, Gloucestershire by Barry Batchelor/PA Photos)

Labels: england, floods

* Posted by damian at 3:54 PM

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