Professor Chris Kilsby comments on how to better prepare for and adapt to flooding in the UK.
There is no panacea for flood events, but there is a portfolio of measures we could either do better or should consider in mitigating or adapting to floods in the UK and countries throughout the world. The recent floods caused by Storm Desmond the first week of December 2015 were devastating on both sides of the Pennines. A record breaking 341mm of rain fell in 24 hours. Not only was the 24 hour rain fall record broken, but so was the 48 hour record at 405mm. The damages were significant with tens of thousands of people evacuating their homes, widespread power loss after two substations were flooded, and transport links lost across the region.
While the magnitude of the storm rainfall was extreme, what made the flood especially severe is that the previous two months were very wet. Extreme weather events like Storm Desmond tend not to occur in isolation and nor are they evenly spaced out. In Cumbria there had already been a cluster of previous storms and this was the big one.
To manage such large floods requires an understanding of the occurrence of sequences of intense rainfall and how they may be changing, but also of course learning to deal with the flood waters in ways that are affordable and sustainable.
1. Come to grips with the role of climate change in extreme weather
Every time an extreme weather event takes place, such as a flood or drought, people ask ‘was that caused by climate change?’ A better question to ask is what fraction of the probability of these events happening is attributable to climate change? This is crucial in preparing for future extreme weather events.
2. Enable cities to have smart forecasting capabilities
There is a global push for cities to become ‘smart’ in anything from how they manage traffic flows to energy use, transport and weather hazards. In addition, water sensor networks and an advanced weather radar station (a local version of what the Met Office and the Environment Agency use across the UK), could be used for forecasting extreme weather giving time for cities to prepare. The Urban Observatory, which will be based at Science Central in Newcastle, collects data that would be of use to managing urban catchments in this way.
3. Improve catchment management upstream and downstream
For the severe flooding that took place in Cumbria, rural land management alone is not sufficient to reduce flood peaks. The level of flooding was so enormous the entire landscape was saturated. Any field scale features that could have been installed to store or slow water flows would have been full. However, such small scale natural flood management has a key role to play in reducing small to medium sized floods which is important for urban and rural areas. Green space, green roof tops, trees, permeable surfaces and above ground water storage all have role to play, but must be planned strategically to make an impact on surface flooding.
4. Make best use of flood defences
Towns and cities like Keswick and Carlisle are defended by purpose designed “hard” defences such as flood walls and embankments. These play a crucial role in defending populated areas, but only to a designed standard of protection (usually 1 in 100 year floods). Alarmingly, the defences in Cumbria had recently been upgraded to our best estimates of this level of hazard, so a reassessment is clearly needed. However, this reassessment must also include the issues of the feasibility and cost of raising these defences further, as there may be limits to how high they can be built and other options may now be preferable.
5. Make best use of large scale water storage
Kielder Water is the largest reservoir in the UK, holding 200 billion litres of water. Even this was not enough to withstand the heavy rains of Storm Desmond. In the winter the level is usually drawn down to give some headroom to store water from rainfall. This is done primarily to prevent spills which cannot be used to generate hydroelectricity. The rainfall from Desmond was so heavy that insufficient headroom was available to hold back the flood. If a strategy was agreed and carried out based on forecasts of heavy rainfall, it could improve flood mitigation downstream, but a balance must be found between energy generation, storing water as a resource and managing large flood events.
6. Look at ways to store water at a rural scale
The use of agricultural rural land to store water to protect cities has never been widely promoted in the UK. Indeed, to the contrary, our twentieth century flood risk management began with the aim of protecting agricultural productive land from flooding. However, water storage on upstream areas does provide a new opportunity. Countries that experience regular monsoon flooding, particularly in Asia, often sacrifice farm land for weeks at a time to curb flows and prevent loss of life and damage. Deliberately flooding the upstream area to avoid the flood wave rushing down to take the lowland city — if done in a cooperative way — could be one of our best defences against large scale flooding.
7. Learn to live with the floods
It is not possible for all settlements to simply seal themselves off from their environment, and learning to live with floods is inevitable. Whether through local catchment management initiatives, community flood defence schemes, retrofitting homes, stronger development control or phased resettlement as we move into a new era of flood risk, we all need to be more flood aware.
Chris Kilsby is Professor of Hydrology and Climate Change in the School of Civil Engineering and Geosciences at Newcastle University. He previously worked as a meteorologist for the UK Met Office. His research focuses on climate change impacts, sustainability and future responses to climate adaptation.