21 November 2006

London below Sea Level

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London planners should prepare for the possibility that the sea level rise will be up to 94 centimetres by the end of this century. But policymakers must be on their marks and keep a watchful eye on the polar ice sheets melt rate, which might further raise the sea level up to 2 metres

London planners should prepare for the possibility that the sea level rise will be up +94 centimetres by the end of this century. But policymakers must be on their marks and keep a watchful eye on the polar ice sheets melt rate and thermal expansion of the oceans, which might further raise the sea level up to 2 metres, although this is thought to be unlikely. The very worst climate change scenario, which is considered to be even more improbable, has now been revised down to +2,7 metres by taking into account the storm surge height and frequency increase in the North Sea, as this is now predicted to be less severe than previously thought.

The thing is, London planners are now beginning to say that they can manage even sea level increases of this size by carrying out changes to the Thames Barrier and raising defences in the estuary along more than 300 kilometres. The first indications coming from Thames Estuary 2100, the project which is producing an adaptation plan and a timescale to protect the UK capital city for the next 100 years, are based on the latest research and modelling they commissioned from the Met Office, the Proudman Oceanographic Laboratory and the Centre for Ecology and Hydrology in Wallingford.

According to them, London is not a disaster waiting to happen. The project, which will go out to consultation next April and is expected to be submitted to the British government by 2010, aims to plan for a variety of scenarios we should be ready for and will be crucial in shaping a realistic flood risk management policy for the Thames Estuary. "The likely sea level rise we are expecting by 2100 is pretty much in line with Defra (the UK Department for Environment, Food and Rural Affairs, Ed.) guidelines, +94 centimetres to be precise", Chris Burnham, senior spokesman for the Thames Estuary 2100 project, says. "In our previous worst case scenario of +4,2 metres we had factored in quite a large amount of storm surge, which in fact may not get significantly worse".

The new +2,7 metre figure comes from the latest Thames 2100 marine study into tidal flooding: "But it’s extremely unlikely", Mr Burnham adds. "It would mean that we would get the worst amount of ice melt, thermal expansion and storm surge all in one". The revised figure means that no outer estuary barrage, which would be the only thing capable to deal with a +4,2 metre rise, will most probably be need to be built this century. But some less populated land may have to be flooded permanently.

"We have found that, with some adaptation to the Thames Barrier and raising of downstream defences, we can manage sea level increases of up to about a metre", Mr Burnham says. "With some further changes to the Barrier and the defences we could cope with maximum water levels up to around +2.5 metres. In order to manage a sea level increase up to about 3 metres, flood storage along the Thames would have to be created and heavy changes to the Barrier would have to be carried out. A brand new Thames Barrier, working in conjunction with the existing one, could manage increases up to around 3,5 metres".

By which time, well into the future, the world would of course be in dire trouble. The European ATLANTIS project, which looked at high theoretical rates of climate change and worst case scenarios, "has helped pave the way to our approach to this adaptation strategy", Tim Reeder, the Thames 2100 project scientist who also took part in the Atlantis case study for London, says. "At Thames 2100 we are keeping up to date with the science. We are saying that we need to be ready to adapt".

There is obvious confidence that the apocalyptic scenario of London under water is destined to be confined to recent disaster films like “Flood” with Robert Carlyle. But it remains to be seen if this new optimism about London’s coping strategies is going to assuage public anxiety, and how the British government is going to make provision for the adaptable plan.

Thames 2100 has also contributed to some of the science that will be published in the next United Kingdom Climate Impacts Programme scenario, which looks at climate change on a national scale and is due out by 2009. Roger Street, the technical director of UKCIP, which was established by the British government over a decade ago to set up local partnerships in order to define and mitigate the implications of climate change, says that "we have to take a risk management approach and deal with this. We have to involve people in these discussions, because there are going to be losses to some areas in the most severe scenarios. We need to agree on what is best for Britain".

The Thames Barrier, Mr Street notes, "has been very effective against tidal flooding, but the flooding risk in London comes from multiple sources, such as fluvial flooding getting into the Thames from the tributary rivers, and flooding associated with the fact that we have paved over a lot of our city and the rainfall is much heavier than it used to be. The real concern arises when these three sources combine".



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