Explaining UK floods

Man-made climate change helped cause south of England floods, say scientists

Katie Hill - Editor-in-Chief, My Green Pod

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Published: 2 February 2016

This Article was Written by: Katie Hill - My Green Pod

  

Human-induced climate change increased the risk of severe storms like those that hit the south of England in the winter of 2013/14, which caused devastating flooding, £451 million insured losses and cost several people their lives.

These are the findings of a new study, published in the journal Nature Climate Change , from an international team of climate scientists led by researchers at Oxford University.

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What caused the floods?

The scientists found that anthropogenic greenhouse gas emissions increased the risk of the once-a-century wet January in 2014 by 43%.

The increase in extreme rainfall that led to the flooding in 2013/14 was the result of two factors associated with global warming: an increase in the water-holding capacity of the atmosphere (a thermodynamic factor) and more January days with westerly air flow (a dynamic factor).

The authors identified that approximately two-thirds of the increased risk could be attributed to thermodynamic changes in the atmosphere, and one-third to dynamic changes.

Impact on the south

Among the worst-affected areas were Somerset, Devon, Dorset and Cornwall in the south west, and the Thames Valley in the south east.

‘We found that extreme rainfall, as seen in January 2014, is more likely to occur in a changing climate. This is because not only does the higher water-holding capacity lead to increased rainfall, but climate change makes the atmosphere more favourable to low-pressure systems bringing rain from the Atlantic across southern England.’

Dr Nathalie Schaller, lead author, Oxford University’s Department of Physics

100k simulations

This first-of-its-kind, end-to-end study looked at the event from start to finish, taking in atmospheric circulation, rainfall, river flow, inundation and properties at risk.

The research made use of the [email protected] citizen-science project, part of Oxford’s climateprediction.net climate modelling experiment, to model possible weather for January 2014 in both the current climate and one in which there was no human influence on the atmosphere. Researchers analysed more than a hundred thousand simulations of possible rainfall in the UK run by citizens from all over the world.

‘The increase in extreme rainfall was due to a rise in moisture and very likely an increase in the frequency of deep depressions west of Scotland. The more extreme the weather, the stronger the effect of climate change over the UK.’

Dr Pascal Yiou, co-author, Le Laboratoire des Sciences du Climat et l’Environnement (LSCE)

The Thames

Hydrological modelling of the Thames river catchment showed that the changes in atmospheric circulation and precipitation caused higher peak 30-day river flow, while flood risk mapping revealed a small increase in flood risk for properties in the Thames catchment.

The heightened risk of rainfall found in the meteorological modelling led to an increase in the peak 30-day river flow of 21% and about 1,000 more properties at risk of flooding.

‘Our hydrological modelling suggests that the increased likelihood of extreme rainfall arising from man-made climate change gives a more modest increase in extreme flows in the River Thames. This highlights the importance of applying hydrological models in order to include the role of the landscape in transforming rainfall into river flows and floods.’

Dr Alison Kay, co-author, Centre for Ecology & Hydrology

Click here to read the article in Nature Climate Change.

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