New modelling techniques disentangle natural fluctuations from effects of increased atmospheric CO2 concentrations
August 29th 2014
Scientists from the Centre of Ecology & Hydrology, the Met Office, and the Universities of Oxford, Exeter and Reading, have carried out a thorough review of the potential influences on the recent floods which devastated large parts of the UK in December 2013 and January 2014. Their investigation examines how factors such as the state of the global oceans may have interacted with wind patterns and subsequent high-level atmospheric features.
Lead author Dr Chris Huntingford from the Centre for Ecology & Hydrology said: “The challenge is to understand in full the subtle balances between the competing influences on UK winter weather, whether they are from the oceans, the amount of polar sea ice, or the atmospheric state itself. Highly refined modelling techniques are now emerging that can tease apart often large natural fluctuations in these drivers from any effects of increasing atmospheric carbon dioxide concentrations.”
The study does not provide a definitive answer as to whether human activity played a role in the magnitude of the UK’s winter floods. The scientists say that many of the possible influences exhibit large natural fluctuations. They believe, however, that the known decreases in Arctic sea-ice cover was not a factor in the particular characteristics of the winter rainfall. Their conclusion is rather that a complex chain of events involving the Pacific Ocean and an unusual jet stream brought about the exceptional nature of the winter flooding.
Co-author Dr Peter Stott of the Met Office said: “More work is needed to robustly detect any changes in storminess in the UK and quantify how the risk of such extreme winters varies with climate variability and change. However, climate models of sufficient resolution to capture storms and their associated rainfall are now becoming available and need to be deployed as soon as possible to provide a solid evidence base for future investments in flood and coastal defences.”
Dr Chris Huntingford added: “The continual advance in scientific understanding of how the climate system operates implies that we will soon be able to assess better if there is any likelihood of the rainfall patterns of last winter occurring with altered frequency. Capitalising also on the UK’s extensive datasets of meteorological and river measurements, in tandem with advanced hydrological models, this understanding can be translated to any expected future flood risk. This review provides a roadmap towards that aim.”
On coastal flooding, co-author Dr Jason Lowe of the Met Office said: “We saw a number of examples last winter that demonstrated the vulnerability of coastal regions to flooding from surge events. At present our best evidence points towards future increases in coastal flooding being driven by global sea-level rise. We still need to better understand if changes in atmospheric storminess can also play a part.”
The research was published on the 27th August in the journal Nature Climate Change. For further information, see the press release on the Centre for Ecology & Hydrology website.
Chris Huntingford, Terry Marsh, Adam A. Scaife, Elizabeth J. Kendon, Jamie Hannaford,Alison L. Kay, Mike Lockwood, Christel Prudhomme, Nick S. Reynard, Simon Parry, Jason A. Lowe, James A. Screen, Helen C. Ward, Malcolm Roberts, Peter A. Stott, Vicky A. Bell, Mark Bailey, Alan Jenkins, Tim Legg, Friederike E. L. Otto, Neil Massey, Nathalie Schaller, Julia Slingo and Myles R. Allen (2014) Potential influences on the United Kingdom’s floods of winter 2013/14. Nature Climate Change, DOI:10.1038/NCLIMATE2314.
Photo: Burrowbridge, Somerset © Copyright Mike Smith and licensed for reuse under this Creative Commons Licence. “Following prolonged rainfall in January 2014, the Somerset Levels were flooded, apart from small areas of higher land.”