The UK has assets worth over £132 billion at risk from coastal flooding and £82 billion from river flooding, and the floods of 2007, with some of the worst affected places in Gloucestershire and an iconic image of Tewksbury Abbey surrounded by water, resulted in an estimated £3 billion of damage. But flooding is not just financial in impact, it is human too. In the 2007 floods some 55 000 homes were flooded and 13 people lost their lives.
The 2007 floods were extreme, like many major floods, but were not statistically rare. Indeed, most years have flood events which have significant impact on local communities. So what constitutes an extreme flood event? Extreme events are measured by impact rather than rarity, and are defined as extreme if they threaten life, cause serious damage to property or vital infrastructure, or significantly change our coastline. Extreme flooding is more often than not the result of a combination of separate, less rare events that in themselves are not unusual, but when brought together result in significant impact. For example, prolonged rainfall, high coastal storm surge and wet antecedent ground conditions.
After the flooding in 2000 the Department for Environment and Rural Affairs (DEFRA) launched its strategy document ‘Making Space for Water’. This, for the first time, articulated the need for a risk-based approach to flood management. But it was the Pitt Review in 2007 that helped lead to the Flood and Water Management Bill, and which in turn helped to establish a new partnership between the Met Office and the Environment Agency in the fore-runner of today's National Flood Forecasting Centre. The Flood Risk from Extreme Events (FREE) programme began before the Pitt Review was commissioned and together with the Flood Risk Management Research Consortium (FRMRC) provided useful background for the UK's continuingly expanding programme of flood risk management, covering ground water, fluvial, pluvial and coastal flooding. The FREE programme made important scientific contributions in each of these areas, some of which are shown in the collection of publications included in this Special section.
The programme was broken down in to four key challenge areas: improving forecasts, understanding uncertainty, the nature of extremes, and the impacts of climate change. The outcomes from these challenges included, amongst others, improved use of a broader range of observations at different scales in flood prediction models, a transfer of knowledge on data assimilation across the different communities working in flood prediction, a greater understanding of uncertainty and its propagation in models through the coupling of cloud-to-catchment-to-coast models, new methods for mapping vulnerable areas, the first ground water flood risk assessment tools, the application of ensemble prediction techniques to catchment and coastal flood models, new methods for quantifying flood risk, changes in heavy rainfall climatology that formed a valuable contribution to the 2009 UK Climate Impacts Programme (UKCIP09) scenarios, and a digitized archive of British Rainfall. Notably, the programme also found significant gaps is our knowledge of pluvial prediction, and in particular surface-water flooding. This is still an area of priority for funding and additional capacity building in the UK.
In addition to the main programmes of work, FREE also collected and established a valuable collection of UK case study data from across a range of flood events, which can be found in the NERC data centre catalogue. FREE also held two national workshops. The first of these was on ‘Using ensemble methods to help improve prediction’ and the second on ‘Precipitation downscaling and modelling’. More information about the FREE programme can be found at http://www.nerc.ac.uk/research/programmes/free/, and the final report (http://www.nerc.ac.uk/research/programmes/free/resources/finale-brochure.pdf) contains details of the full list of publications.