16 february 2011

Emissions contributed to Autumn 2000 flood risk

Science | Environment

Flooding along the river Ouse in York in Autumn 2000.
Flooding in York in Autumn 2000. Photo: Gordon Hatton

Greenhouse gas emissions due to human activity substantially increased the odds of damaging floods occurring in England and Wales in Autumn 2000 according to new research published in the journal Nature this week. Although the precise magnitude is still uncertain, the researchers found a 2-in-3 chance that the odds were increased by about a factor of two or more.

The floods of autumn 2000 damaged nearly 10,000 properties, with insured losses estimated at £1.3 billion. The study suggests that, although these floods could have occurred in the absence of human influence on climate, greenhouse gas emissions can now be blamed for increasing the odds of floods occurring at that time.

Dr Pardeep Pall, who initiated the research as a Doctoral student at Oxford University’s Department of Physics, said: ‘This study is the first of its kind to model explicitly how such rising greenhouse gas concentrations increase the odds of a particular type of flood event in the UK, and is the first to use publicly volunteered computer time to do so.’

Using a detailed computer climate model, developed at the Met Office Hadley Centre, the project team simulated the weather in Autumn 2000, both as it was, and as it might have been had there been no greenhouse gas emissions since the beginning of the 20th Century. This was then repeated thousands of times using a global volunteer network of personal computers participating in the climateprediction.net project in order to pin down the impact of emissions on extreme weather.

In collaboration with Risk Management Solutions (RMS), developers of risk models for the insurance industry, the team then fed the output from these weather simulations into a flood model, and found that 20th-Century greenhouse gas emissions very likely increased the chances of floods occurring in Autumn 2000 by more than 20%; and likely by 90% (close to doubling the odds) or more.

Professor Myles Allen, of Oxford University’s Department of Physics and School of Geography and the Environment, a co-author of the paper, said: ‘whether or not a flood occurs in any given year is still an ‘Act of God’ but, with the help of thousands of climateprediction.net volunteers, we are beginning to see how human influence on climate may be starting to load God’s dice.’

we are beginning to see how human influence on climate may be starting to load God’s dice.

Professor Myles Allen

Dr Dag Lohmann of RMS, a co-author on the paper, said: ‘studies like this are helpful, since we need to know how risks are changing to provide our clients with accurate models of risk today.’

Dr Peter Stott, of the Met Office, also a co-author, said: ‘This study is the first step toward near real-time attribution of extreme weather, untangling natural variability from man-made climate change. This research establishes a methodology that can answer the question about how the odds of particular weather events may be altering. It will also allow us to say, shortly after it has occurred, if a specific weather event has been made more likely by climate change, and equally importantly if it has not.’

Dr Richard Harding, of CEH Wallingford and the coordinator of the EU WATCH project which co-funded this research, said ‘climate change is only one of many factors  affecting local flood risk, but understanding it is clearly important if we are to plan how to adapt.’

Members of the public can still participate in follow-up studies, supported by Microsoft Research, Oxford University’s Smith School for Enterprise and the Environment, the Met Office, and the Natural Environment Research Council, to assess how emissions might have changed the odds of a whole host of weather-related events – including floods and droughts – in regions across the world: more details at http://weatherathome.org.

A report of the research, ‘Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000’, is published in the journal Nature on 17 February.