Filip Babovic (Department of Civil Engineering) (@filipbabovic) looks back on the record-breaking floods experienced in the UK last December, asking whether we should expect such extreme weather to become the norm and how we can defend ourselves against future flooding.
The UK has a reputation for being rainy, but last December it saw a deluge of truly epic proportions as the country was battered by storms Desmond, Eva and Frank. With 191% of average rainfall, it was the UK’s wettest December, and calendar month, since records began 105 years before (according to Met Office figures).
The most extreme conditions affected western and northern regions of Great Britain, where rainfall reached two to four times average levels. The precipitation experienced in some areas surpassed anything seen before: in early December, 341.4 mm of rainfall dowsed Honister Pass in Cumbria in 24 hours, setting a new UK record for any 24-hour period.
The effects of this extreme precipitation were exacerbated by saturated ground conditions following a wet November. Waterlogged areas meant that incoming rainfall could not infiltrate the soil and therefore remained on the surface, leading to flooding in many regions.
A “new normal”
Politicians and the media were quick to suggest that these flooding events could represent a “new normal”. In a recent interview, First Minister of Scotland Nicola Sturgeon noted for instance that the “unprecedented weather …will become more commonplace”.
I doubt that the flooding we saw in the North will occur every winter, but climate change will certainly increase the risks of hydrological extremes. A preliminary investigation has found that the heavy rainfall observed was 50-75% more likely due to the effects of climate change. The UK Climate Projections also predicts that winter precipitation depths across most regions of the UK will increase with climate change.
However, separating the effects of climate change from natural variations in climate is difficult and it remains a challenge to identify the climate change signal.
How do we adapt?
One of the towns affected by the recent flooding in December was Cockermouth, which has experienced many recent spates of flooding, including 2005 and more famously 2009. In 2013, a £4.4 million flood defence scheme was completed. Visiting Cumbria as part of my master’s studies in 2014, I was impressed with the scheme and the care that had been taken to preserve the town’s ambiance. The town’s defences consisted of a number of floodwalls that were built to match the town’s Georgian architecture and a sacrificial flood plain, which allowed for the management of raised river levels in times of flooding.
But the question remains: why did a recently built and well designed flood protection scheme fail within such a short period of time?
The world is changing and many of the assumptions previously made about planning with regard to the magnitude of climate events and the demands imposed by populations are no longer valid. Much of the UK’s infrastructure system needs to be adapted and renewed, in 2014 The Institution of Civil Engineers gave the UK’s flood defence infrastructure a grade of C-.
Planning in uncertain times
It’s clear that our infrastructure is in desperate need of an upgrade but determining how to design future-proof infrastructure is not clear. Many large uncertainties remain about the weather conditions we may face in future and many of the assumptions made in infrastructure planning could be wrong.
Global Circulation Models, which we use for making large-scale climate predictions, are of limited effectiveness for delivering information about local conditions and changes. At the same time, there is large uncertainty surrounding potential land use change. The interaction of these factors has led to a condition known as deep uncertainty, meaning that we cannot easily characterise future conditions.
There are two primary ways of dealing with these uncertainties. One method is to build larger defences that are able to protect against a much wider range of weather events. However, this strategy can quickly become expensive as construction costs can skyrocket.
Alternatively, one can adopt a flood defence strategy that is flexible and updated regularly. By having a more active management approach, we can respond to change and make the right adaptation at the right time. This avoids the expense incurred by large defence schemes but does impose an additional organisational burden on flood defence authorities.
My own research is on developing flexible strategies to help cities defend themselves against flooding, taking into account the potential effects of urban growth and climate change.
I believe that flexible and adaptive strategies are the best way of dealing with an uncertain future. Given the very wide range of possible future conditions, a single static strategy will either be too inflexible or too expensive to be practically feasible. Future infrastructure should therefore be designed to allow for incremental changes to our systems and be thought of as one part of a larger, long-term adaptation strategy.