Tuesday, 11 February 2014

Scientists from CEH and BGS comment on the ongoing flooding situation in the UK - 11 February 2014

Scientists from the Centre for Ecology & Hydrology and their NERC colleagues in the British Geological Survey have provided the following comments on the ongoing storms and flooding situation in the UK.

We published further comments on 13 February 2014. Read them here.

Mr Terry Marsh, Leader of the National Hydrological Monitoring Programme, Centre for Ecology & Hydrology

"One of the issues for the public perception to take on board is what we are currently seeing is the Thames exercising its natural sovereignty over its floodplain. This happens occasionally and in a sense it’s good for people to recognise that this happens. Management needs to limit the damage but it would be, I suggest, even worse if we found ourselves in the position where people thought because we’ve not seen this extent of flooding for 40 years that it’s not going to happen. It’s a natural part of the way rainfall patterns translate into river flow patterns."

Dr David Boorman, Science Area Lead for Water Resources, Centre for Ecology & Hydrology

"A key question in any unusual hydrological situation, such as a drought or a period of wet weather as we are experiencing now, is how long will it continue? We are working with a number of partners to provide a long-range hydrological forecast for the UK. Forecasts of this type are already produced on an operational basis in a number of countries including the USA and Australia.

“The project involves bringing together information on the current weather, soil moisture, river flows and groundwater levels from across the UK, and using a number of methods of exploring possible future hydrological conditions, for example, using numerical models of river flows and groundwater models driven by long-range weather outlooks."

Mr Nick Reynard, Science Area Lead for Natural Hazards, Centre for Ecology & Hydrology

"The cluster of drought and flood events through the early years of the 21st century and the recent runoff and recharge patterns, are near to the extreme range of historical variability as we currently understand it , and therefore also raise the question that they may reflect anthropogenic climate change. It is important to note, however that how river flows respond to extreme rainfall varies greatly because of geology, soils, land use etc, meaning that it is difficult to detect signals of climate change in observed events, and to generalise the impacts of climate change for future flooding. Tidal flood risk is increasing as sea levels rise but the outlook is more complex in relation to fluvial flooding."

Prof Alan Jenkins, Director of Water and Pollution Science, Centre for Ecology & Hydrology

"The long duration of the current flooding episode and its wide spatial extent make it an exceptional event. Relentless storm events over many weeks have combined to produce widespread flooding at a scale rarely seen in the UK. Over 5000 homes have flooded and transport infrastructure has been disrupted across the UK.

“The key to mitigating the impact of any flood is understanding that every catchment works in a different way. For example the current flood situation on the Somerset Levels is the result of a different range of processes to those currently affecting the lower reaches of the River Thames. The operational agencies are doing a sterling job on the ground and it’s important to recognise that hundreds of thousands of homes have been protected by the UK’s flood defence infrastructure.

“Many potential solutions have been talked about over the last few weeks as ways of minimising flood risk. This is a complex issue and over the next few months it is important that experts from the key agencies and research institutes sit down and carefully analyse whether there are lessons to be learnt from the current flood episode."

Dr Chris Huntingford, Climate Modeller, Centre for Ecology & Hydrology

"In terms of climate change, there is a desperate need to move away from the almost Punch-and-Judy debate of either every extreme is due to climate change, or the contrast of everything is simply natural variability. Desperately needed is the on-going calculation of whether higher atmospheric concentrations of carbon dioxide are changing the chances of rainfall events, as recently witnessed, occurring.

To work this out, weather forecast models that analyse the atmosphere in such fine detail as to model storm tracks, need to be operated for different levels of modelled carbon dioxide. Running these for hundreds of modelled years for alternative carbon dioxide concentrations, so as to build up statistical profiles of rainfall patterns, presents one of the biggest computational challenges ever tackled."

Mr Simon Parry, Hydrologist, Centre for Ecology & Hydrology

"Each one of these individual events has not been particularly outstanding, they've been broadly along the lines of what we would expect for a typical winter storm in the UK. What's been notable about it, and different from what we've seen in the past, is the persistence. The combination of high tides, strong winds and a succession of rain-bearing low pressure systems has led to widespread and sustained high flow conditions over a two month timeframe."

Mr Andrew McKenzie, Groundwater Information Manager, British Geological Survey

"In early December 2013 groundwater levels over much of the UK were normal for the time of year. The extreme rainfall in the southern part of England over the New Year and into early January had a dramatic impact on levels in the faster responding aquifers and spectacular rises occurred in groundwater levels in some aquifers. For example, groundwater levels in the Chalk at Tilshead on Salisbury Plain rose by about 20 metres in just two weeks. These rapid rises triggered some localised groundwater flooding, mainly in the upper parts of Chalk catchments. If rainfall had eased at that point the empty storage in the lower catchment might have been able to absorb the inflows. However, as rainfall has continued to fall the lower parts of many catchments have been saturated, and prolonged high river levels will have contributed to exceptional recharge.

“At the beginning of February record monthly groundwater levels were measured across many aquifers, and as levels in February are naturally high, these records are often all time records for the sites concerned. Record levels were established in the Chalk of Wessex, the North Downs and Hampshire. The wet weather also reversed a declining trend in some of the North West Permo-Triassic aquifers.

“Consequently, emergence of groundwater has been observed at many localities across southern England where groundwater flooding has been previously recorded. The high water levels on the interfluves (the upper parts of groundwater catchments) will gradually feed into the lower parts of the catchments, over a period of weeks to months, so groundwater flooding is expected to persist."

Additional information

Journalists can contact the CEH Press Office or the BGS Press Office for further context on the UK's hydrological situation. 

Further information from CEH can be found in the following blog posts:

Record breakers? Climate change, statistics and the recent UK floods - 9 February 2014

Rainfall, UK floods and the potential impacts of climate change? - 6 January 2014

CEH worked with the Met Office on a report on the recent storms and floods in the UK.

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