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Parts of the UK have experienced severe flooding due to major storms (Storm Ciara and Storm Dennis) on consecutive February weekends.
Thursday 20th February
Professor Ian Cluckie, FREng, Emeritus Professor of Engineering, Swansea University, said:
“The current floods being experienced across the United Kingdom are severe and in places unprecedented. The relatively warm winter has so far encouraged flooding as a succession of storms have increased the wetness of soils and allowed extremely high rainfall rates to be produced by relatively warm air carrying more moisture. The current culprit named “Dennis” has affected many places in England and Wales with the Rivers Severn and Wye plus their tributaries achieving “Red Warning Status”. The Capital City of Wales – Cardiff – apparently lives to fight another day. Yet more storms are expected, and the overall outcome is yet to be determined. The rainfall forecasting provided by the Meteorological Office has been excellent and the various Government Agencies (EA, SEPA and the NRW) have provided increasingly accurate forecasts for rivers on the UK mainland. The recently agreed provision of £1.2 Billion by Government for a new supercomputer for the Meteorological Office will allow the development of even higher resolution modelling capabilities in both the weather forecasting and climate modelling domains. However, government still faces the decision on how much money should be provided in the future in order to mitigate flooding in an increasingly changing and hostile climate. Perhaps at last the untouchable building regulations will be revisited in relation to building on floodplains?”
Tuesday 18 February
Jamie Hannaford, Principal Hydrologist at the UK Centre for Ecology & Hydrology:
“Analysis of river flow records extending back five decades or more has shown increasing flood severity and frequency, particularly in winter in the upland northern and western parts of the UK. It is not possible to attribute these trends fully to human-induced climate change. However, the trends are consistent with what one would expect from a warming climate, given the well-established link between a warmer atmosphere and increasingly heavy rainfall, and some studies have demonstrated a link between human warming and other recent flood events.
“Making comparisons between flood events is difficult because there are many different aspects one could compare, such as highest peak levels, the spatial area affected, duration of the flood and the scale of the impacts. While events are still unfolding, and it will take time for comprehensive analysis, it seems likely the combined effect of storms Ciara and Dennis has caused an exceptional and widespread flood episode at the national scale, comparable in significance with other major flood episodes of recent years, such as winter 2015-2016, winter 2013- 2014, 2012 and 2007.”
Prof Roger Falconer FREng, Emeritus Professor of Water Engineering at Cardiff University and a Fellow of the Royal Academy of Engineering, says:
“The challenge of flooding often arises in steep catchments where the water drains rapidly off the steep upper reaches and then flows much slower on the flatter land further downstream, as is the case for much of the recent flooding we have seen. In my view the most viable solution for the future in many parts of the UK is to build flood control dams, often referred to as flow-through or perforated dams1, which are specifically designed for flood mitigation, such as the Masudagawa Dam on Japan’s Masuda River. Such a dam fills during flooding in the upper parts of the river basin and is then emptied, under controlled conditions, after the flood.
“The principle is similar to natural flood management, which uses woody dams and plants trees etc. in the upper reaches of river catchments to hold back the water. However, for some of the recent floods we have experienced, woody dams and trees alone cannot address the challenges of significant rainfall events, and the Met Office is predicting up to a 30% uplift in rainfall2 in the future. Larger dams can hold back much larger volumes of water – dams like those outlined above are quite common in the US.”
1 https://www.ctc-n.org/technologies/flow-through-dam-flood-control
2https://www.gov.uk/government/publications/national-flood-resilience-review
Prof Jim Hall FREng, Professor of Climate and Environmental Risks at the University of Oxford and a Fellow of the Royal Academy of Engineering, says:
“There is a wide range of possible responses to flooding:
“None of these alternatives can ever be 100% effective and usually they will work best if done in combination. The best combination of interventions will depend upon the characteristics of particular places. Choosing what to do involves considerations of the severity of the risk, affordability and of other impacts e.g. on the natural environment. The impacts of climate change mean that designing interventions to manage flood risk is becoming more difficult, because the future is more unpredictable. It is therefore important to continue to monitor changes and modify flood risk management when we discover more about how the climate is changing.”
Dr Jess Neumann, Flood Scientist, University of Reading, said:
“Parts of the UK have experienced more than one months’ worth of rainfall over the last 2 days with Storm Dennis. This persistent and heavy rain has fallen on ground already saturated by Storm Ciara last weekend, leading to the Environment Agency issuing a record number of flood warnings and flood alerts (more than 600 on Sunday evening, including 4 severe warnings meaning a danger to life on the River Teme). Flood defences are in operation and additional temporary flood barriers have been installed across the country reducing the risk of flooding to properties and businesses.
“In the south-east, tributaries of the Thames including the River Mole and River Wey are rapidly approaching levels experienced during the Christmas floods of 2013 which saw large parts of Surrey and Thames Valley underwater. Much of the flooding is being caused by heavy rain falling on ground already saturated by Storm Ciara last weekend. At 7 pm on Sunday evening, levels on the River Mole at Dorking reached 2.1 m – just 64 cm off the highest level ever recorded (Tuesday 24th December 2013), while the River Wey at Farnham reached 1.156 m, just over 11 cm off its record level set in October 2000. Levels on both rivers are still rising and flood warnings are in place across the county with flooding of property, businesses, farmland and roads expected. River levels are expected to remain high through Monday. Local communities are advised to plan their routes carefully, avoiding low-lying roads and pathways. Property and valuables at risk of flooding should be moved to safety wherever possible.
“Whilst it is not possible to attribute one event such as Storm Ciara or Storm Dennis to climate change, there is increasing evidence that periods of intensely strong winds and heavy rainfall are likely to increase with climate change. A warming atmosphere can hold more moisture making heavy rainfall and flooding more likely in the future. As a nation we need to be prepared for more stormy weather and flooding by taking steps to appropriately manage flood risk. These include maintaining existing flood defences and introducing more soft engineering solutions through natural flood management, improving resilience to transport networks and making sure people are informed about potential flood risks in good time.”
Dr Michael Byrne, Lecturer in Climate Science at the University of St Andrews and Research Fellow at the University of Oxford, said:
“More water in the atmosphere is an inevitable consequence of global warming. This means that in many parts of the world – including the UK – rising temperatures and heavier downpours go hand in hand. Although the fingerprints of climate change are all over this weekend’s flooding, the jury is still out on whether global warming will strengthen or weaken the winds of storms like Ciara and Dennis.”
Professor Marc Stutter, The James Hutton Institute, Aberdeen, Scotland, said:
“Such storms are part of shifting baseline for the climate and the state of the landscape on which the rain falls. Whilst future scenarios for rainfall and runoff are highly uncertain there is less doubt that the future has greater variability in extremes of rainfall, both times of flood and droughts. This demands more consideration into how we plan water into places to live and work as well as into the rural land that provides the majority of the space rainfall lands on. The concept of speeding runoff water’s passage through land, pipes and channels is not always sustainable; it might work if unimpeded all the way to the sea, but that seldom happens, instead it arrives rapidly at one pinch-point with worse consequences. Development has removed many areas of infiltration into soils and green spaces in our landscape that buffer against peak and low flows. Infiltration and places to slow, store and filter water need to be planned back into landscapes to add resilience to floodwalls; the alternative is we risk raising the walls every few years.”
Dr Len Shaffrey, Senior Research Scientist, University of Reading, said:
“We expect that mid-latitude storms over the UK (such as Ciara and Dennis) will become slightly more frequent under climate change. Climate change also means that storms will become warmer and wetter and so will produce more rainfall.
“The combination of wetter and slightly more frequent storms in the future means that the UK will have to adapt to an increased risk of wintertime flooding in the future.”
Dr Mohammad Heidarzadeh, Head of Coastal Engineering and Resilience LAB, Brunel University London:
“Flooding brought by Storms Ciara and Dennis reveal that the UK’s flood defence systems, which were developed decades ago, are not fit to address the current climate situation which is characterised by high frequency and high intensity climate events. While the interval for major floods was 15-20 years in the past century in the UK, it has dramatically shortened to 2-5 years in the past decade. Therefore, it is no surprise that several flood defence systems were overtopped or damaged by flood water.
“Given the major flooding in the past couple of weeks (and past few years) and changes in the frequency and intensity of weather incidents, it appears that our flood defence systems require improvement.
“The solution to the flood problem in the UK definitely is not structural. We hear some experts and public ask for construction of more flood defence structures, but structures alone may not help and sometimes even can make the situation worse.
“We need a holistic, integrated approach which means a combination of structural and non-structural approaches as well as significant public involvement. Non-structural solutions such as managed retreat, sustainable drainage systems and public involvement are vital. The country needs further investment in its flood systems, but such investment should be within in a holistic and integrated framework.”
Declared interests
None received.