December 11, 2015, by Charlotte Anscombe

Are the Cumbria floods due to climate change?

The current floods that have affected parts of Cumbria, Lancashire and south Scotland have been caused by unprecedented amounts of rainfall. This has led a lot of people to understandably raise a number of important issues and questions, such as: is the flooding a a sign of climate change; how unusual has the rainfall been over the past week; and why has flooding occurred even when new flood protection schemes have recently been put in place?

Dr Simon Gosling, Associate Professor in Climate Risk at the School of Geography, shares his opinion on some of these issues.

What caused the flooding and how severe has it been?

The rainfall we saw over the weekend of 5-6 December was caused by a steady flow of wind from a south-west direction. The winds came from the Caribbean and Gulf of Mexico in the West Atlantic. This means the air was carrying a lot of moisture as a result of water evaporating from the ocean surface, into the atmosphere. However, the air was unusually moist and this is possibly due to the fact that ocean temperatures in the west Atlantic are currently a lot warmer than normal.

The El Nino that occurs over the Pacific, may also have played a role. Last month the Met Office noted that this year’s El Nino is particularly strong and they noted at the time that this poses a risk for higher than average rainfall in the UK between December 2015 and January 2016.

Over 5,200 homes and businesses have been affected by the flooding. The latest estimate is that Storm Desmond has cost £400-500 million of damages. This compares with £275 million worth of damages, which was recorded during the 2009 Cumbrian floods. It’s also likely that there will be longer term-effects. It can take several months for homes and offices to be cleared out, sanitised and re-instated after severe floods like this. The effects can also have emotional and psychological effects on the people affected, which can last for many years after the event. Cases of anxiety and depression in the years that follow have been seen after other past floods in the UK.

Why is the rainfall of the past week described as unprecedented?

Because we have seen the wettest single day ever recorded in the UK. On 5th December 2015, 34cm of rainfall fell in one day at a weather station at Honister Pass in the Lake District. To put this into perspective, this region would typically on average see around 1cm of rainfall each day in December. The previous record was 32cm, which was also recorded in the Lake District at Seathwaite, back in November 2009. We’ve also seen a new 2-day record set: 41cm of rainfall was recorded over two days at Thirlmere in Cumbria.

 Is the flooding due to climate change?

It’s too early to say, but it is the kind of event we would expect to see if we consider what climate models tell us the potential effects of climate change will be on the UK over the decades ahead: increases in winter rainfall, more days of heavy rainfall, and milder winters.

We are seeing more extreme weather events and evidence is now starting to point towards climate change as being party responsible. For example, Met Office research published in 2014 shows that the chances of Europe experiencing an extreme heatwave like the 2003 event have increased from around 1-in-1000 years to around 1-in-100. In terms of flooding, another report from the Met Office shows that for the same weather pattern we have seen over the past week or so, a long period of high UK winter rainfall is now 7 times more likely to occur, compared with an alternative world without human emissions of greenhouse gases.

Why did the flood defences fail in so many places?

Flood defences are built to be able to stand up to a certain level of flood. Engineers often refer to these levels in terms of their so called “return period”, which is a statistical estimate of how often a flood of a certain magnitude is likely to occur, based upon past flood levels, e.g. 1 in 50 year, or 1 in 100 year flood.

Several of the defences that we have seen over-topped this past week were designed to protect against a 1-in-100 year flood. Understandably, many people are now asking why they were not designed to deal with a higher level of flood, like a 1-in-200 or 1-in-500 year flood. The inconvenient fact is that at some point in the future, any reasonably built flood defence that is designed to stand up to a certain level of flood will likely be over-topped, since floods are by definition, extreme events.

Nevertheless, it is concerning that so soon after new and upgraded flood defences were put in place following the 2009 floods in Cumbria that we are seeing people being affected by flooding again in the same areas. It raises the question of whether it is time to reassess the standards of flood protection that are built in flood prone areas, to lower the risk of these kind of devastating events occurring.

The Environment Agency aims to provide the best possible protection for a community that can be justified technically and economically, and which actually fits within the community. So, whilst flood defence walls several meters high could be constructed along the banks of a river, it would in turn prevent people from enjoying the river and the space it offers during the larger part of the time when the river is not in a state of flood – factors that make such areas attractive places to live. The Environment Agency consider factors such as risk of loss of life, potential physical and economic damage, and hydrological models that show the behaviour of floods, to decide where to prioritise the planning and construction flood defences.

How has the Government responded?

The Government announced this week that they will offer £500 to homeowners who need temporary accommodation. They also announced that a grant of up to £5,000 would be available to pay for barriers, waterproof doors and higher electrical sockets to protect peoples’ homes from future flooding. They will also offer businesses up to £2,500 to help them to resume trading and the Environment Agency are to be given £10 million to repair flood defences that have been damaged as a result of the floods.

 (Images sourced from Xpert)



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