Experts discuss changing extremes in hydrology in the UK

The conference ‘Changing extremes in hydrology’ was held at Exeter College in Oxford on 15 April 2013, and examined the characteristics and impacts of the extreme hydrological conditions experienced in the UK during 2012.

The conference’s theme was inspired by the extraordinary nature – in hydrological terms – of 2012. The first three months of 2012 were marked by the on-going drought which began in 2010. In early April water companies were forced to issue water use restrictions, affecting 20 million users. Then just a few days after the restrictions were imposed, a period of intense rains commenced and continued for the entire summer period, making it the wettest summer in the past 100 years. This prolonged period of rain resulted in widespread flooding across the country throughout the remainder of the year.

The aim of the conference was to review the meteorological and hydrological conditions that characterised 2012, to review the economic damages associated with the drought and flooding, and to provide a broader conceptual framework for understanding how the occurrence of extreme hydrological events might change in the future as a result of climatic changes and other drivers.

Mike Kendon from the Met Office opened the event by describing the characteristics of the 2010-2012 drought and placing it within the context of previous droughts across England and Wales. The drought was one of the ten most significant of the last century, but what was really remarkable was its sudden end in the spring of 2012 with the onset of greater than average rains.

This sudden transition from too little water to too much water was discussed by Simon Parry from the Centre for Ecology and Hydrology. Parry explained how a shift in the jet stream in the spring of 2012 provided the climatic conditions necessary to produce two of the wettest months on record. This rapid change from drought to flood conditions had massive impacts on farmers, explained Tim Hess from Cranfield University. He pointed out that very few farmers are insured against flood damage and recommended a series of measures to make the UK agricultural industry more resilient to weather-related shocks.

Stuart Hyslop from the Environment Agency spoke about the effects of the 2010-2012 drought on water supply in the Thames region. He pointed to the increasing sectoral competition for water for agriculture, domestic use, recreation and wildlife during low flow periods. In order to resolve this conflict, the Environment Agency has a role in monitoring and coordinating the different water users to ensure that an equitable balance is struck between users wherever possible. Edmund Penning-Rowsell, Visiting Research Associate at Oxford University, described the damages caused by the 2012 floods.  Comparing the damage with that of historical floods, he showed how economic losses caused by flooding are overestimated in the UK.

Bill McGuire, University College London, addressed the problem of extremes from a broader perspective, providing examples of how changing climate triggers geological events such as volcanic eruptions and tsunamis. He suggested that changes on the Earth’s surface induced by climatic changes, such as ice sheet melting and sea level rise, may trigger geological catastrophes. This may imply that in the future we might witness “geological mayhem as well as climatic mayhem”, he said.

Patrick McSharry from the Smith School of Enterprise and the Environment, Oxford University, discussed the contribution of mathematical statistics and the theory of extreme values to quantifying risks associated with extreme weather events, enabling better estimates of the levels of risk associated with catastrophic events.

Bruno Merz from the German Research Center for Geosciences discussed the linking of observed changes in flood frequency with specific drivers. While it may be easy to detect changes in flood frequency, separating the effects of drivers such as climate change, dam building or land use change on flooding is much more difficult and requires further research effort. This issue was also taken up by Thomas Kjeldsen from the Centre for Ecology and Hydrology, whose research investigates the effects of urbanisation on a catchment’s flood response. Comparing pre-urbanisation and post-urbanisation flood data has increased understanding of how urbanisation affects flooding frequency.

The final presentation by Harvey Rodda, Hydro-GIS Ltd, considered the nature of floodplain development in the UK and how flood risk is incorporated within the planning process. A number of examples showed how flood risk may, in some instances, be used as a lever against problematic planning applications.

The conference demonstrated clearly the need for further research to link observed changes in flood frequency to drivers, and to better understand and manage rapid shifts from drought to flood conditions. At the intersection between research and policy, thinking should be devoted to investigating risks associated with extreme events, and to means of financing these risks and sharing the burden of extreme hydrological events across society. In terms of policy-relevant findings, a better understanding and an unbiased representation of the damages caused by hydrological extremes is required to prioritise flood protection investments and also to reduce the chances of inappropriate use of flood risk information in planning.

The conference was organised by Hydro-GIS Ltd, a UK-based hydrology and GIS consultancy company, and received sponsorship from Oxford University’s Smith School of Enterprise and the Environment. Visit the conference website

By Edoardo Borgomeo, DPhil student at the Environmental Change Institute

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