Record rains scuttle UK floods strategy #ClimateChange #Floods

The floods that hit the UK last winter were the most extreme on record – and they may be a sign of worse to come.

The UK has been warned that it needs to carry out a complete overhaul of its flood defence strategy following the devastating floods that hit northern Britain and Northern Ireland last winter.

A comprehensive review of the impact of a series of prolonged downpours between November 2015 and January 2016 concludes that there is an urgent need to adapt engineering designs and flood management strategies.

The National Hydrological Monitoring Programme study, carried out by scientists from the Centre for Ecology and Hydrology (CEH) and the British Hydrological Society, is published today on the anniversary of Storm Desmond − the most destructive of several named storms during three months of “remarkably persistent and exceptionally mild cyclonic” activity.

Wettest and warmest

The scientists rank last winter’s floods alongside the floods of 1947 as the two largest flood events for at least 100 years.

Last December was the wettest and warmest since 1910, with record river flows logged at 24 monitoring stations. In the English Lake District, a record of 341mm was set for the level of rainfall in 24 hours.

Potentially more worrying, the 2015/2016 floods appear to be part of a trend over recent decades for more frequent extreme winter rainfall events.

This is consistent with analysis by the UK Meteorological Office suggesting that storms bringing extreme wet weather are seven times more likely as a result of climate change.

“ Recent modelling studies do point towards
human-induced warming having a role
to play in these and other recent floods ”

The authors of the latest study stop short of attributing the 2015/2016 floods to climate change, pointing out that identifying trends can be challenging because records are held over a relatively short timespan.

However, they acknowledge that average temperatures across the UK have increased by more than 1°C over the last 100 years, with a particularly steep rise since the early 1960s.  This is reflected in rising sea levels and a corresponding increase in the risk of tidal flooding.

They cite a preliminary study released shortly after the December 2015 floods, suggesting that extreme rainfall events such as those associated with Storm Desmond were 40% more probable as a result of anthropogenic warming.

And they point to new data from the UK Benchwork Network of gauging stations, showing that in western parts of the UK there has been a steady increase in high winter river flows from the 1950s to 2013.

Lead author Terry Marsh, senior hydrologist at CEH, says: “At a national scale, the winter floods of 2015/16 were the most extreme on record. The November to January period was the wettest three-month sequence in the UK rainfall series – which begins in 1910.

Insurance bill

“The associated flooding was both extensive and repetitive, and total river outflows from Great Britain following the passage of Storm Desmond in December exceeded the previous maximum by a substantial margin.”

Storm Desmond alone caused an estimated insurance bill of more than £1.3 billion when it struck on the 5th and 6th of December last year.

A total of 16,000 houses and factories in England were flooded. Across northern England, Scotland and Northern Ireland, floods caused landslides, road and rail closures and damage to more than a hundred river bridges.

The report’s co-author, Jamie Hannaford, principal hydrologist at CEH, says: “There is much natural year-to-year variability, which makes it hard to attribute observed trends to climate change.

“Nevertheless, recent modelling studies do point towards human-induced warming having a role to play in these and other recent floods.”