Spatial analysis and simulation of extreme coastal flooding scenarios for national-scale emergency planning

¹ HR Wallingford, Howbery Business Park. Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BA, UK
² Ocean and Earth Science, National Oceanography Centre, University of Southampton, European Way, Southampton, SO14 3ZH, UK
³ Environment Agency, Manley House, Kestrel Way, Exeter, Devon, EX2 7LQ, UK
⁴ Natural Resources Wales, Wales, UK
⁵ Environment Agency, Thames Barrier, Eastmoor Street, London, SE7 8LX, UK

^a Corresponding author: d.wyncoll@hrwallingford.com

Abstract

The UK has a long history of coastal flooding, driven by large-scale low-pressure weather systems which can result in flooding over large spatial areas. Traditional coastal flood risk analysis is, however, often undertaken at local scales and hence does not consider the likelihood of simultaneous flooding over larger areas. The flooding within the UK over the Winter of 2013/2014 was notable both for its long duration, lasting over two months, and its spatial extent, affecting many different areas of England and Wales. It is thus apparent that to plan and prepare for these types of extreme event it is necessary to consider the likelihood of flood events arising at different locations simultaneously (i.e. to consider the spatial dependence of extreme flood events). This paper describes the application of a state-of-the-art multivariate extreme value methodology to extreme sea levels and wave conditions around the coast of England and Wales. The output of the analysis comprises a synthetic set of extreme but plausible events that explicitly captures the dependence between sea conditions at different spatial locations around the coast. These simulated extreme events can be used for emergency management and advanced flood risk analysis.