December 2015: Desmond, Eva and Frank cause flood chaos and despair
SurgeWatch focuses on coastal floods, but in view of recent events it’s relevant to discuss the severe non-coastal flooding that has dramatically impacted the UK this winter.
Provisional statistics from the Met Office showed that December broke records for rainfall and temperature, with some locations unfortunate enough to be in the path of ‘atmospheric rivers’ (a phenomenon forewarned of by researchers in 2013). For example during ‘Storm Desmond’, from 4-5 December 2015 Honister (Cumbria) experienced 341.4mm (13.4in) of rain in 24 hours! The entire month witnessed persistent flooding across large areas of Ireland, England, Wales and Scotland. On Boxing Day in Yorkshire there was flooding of over 600 homes along the banks of the Ouse and the Foss, and remarkable scenes as the city of York was flooded. More than 5,200 properties were flooded in Cumbria and Lancashire and 20,000 homes were left without power across the UK. As a result of storms ‘Desmond’ and ‘Eva’, over 16,000 homes in England are estimated to have been flooded. There was also repeated inundation of homes during the same month. The Association of British Insurers have estimated that nationally this winter’s storms are likely to cost upwards of £1.3 billion, although the overall cost may exceed £5 billion.
The roles of climate change and El Nino will feature in reflection upon why the rainfall was so intense and prolonged. Also, among the many other aspects that will be scrutinised in the aftermath are land use management and the resilience of flood infrastructure. In the case of the former development on floodplains is an obvious concern, whilst land and river management encompass a range of hugely complex issues. I remember learning during a GCSE geography fieldtrip how sphagnum moss (that forms peat) holds astounding amounts of water, and is one of many components that can regulate the flow of rainwater through a catchment and affect flooding. However, of the peatlands which cover 12% of the UK, 80% are in a poor condition. On a different note, the December floods exposed some weak links in defences – for example the raising of the Foss Barrier seemed an odd decision, but due to the location of electrical equipment the barrier was at risk of being stuck in the ‘down’ position (and subsequently would have been unable to discharge water into the River Ouse).
The 2015/16 winter floods follow a succession of extreme events. Perhaps the onset of this chain is marked by the flash flood in Boscastle (Cornwall) on 16 August 2004, which was followed by longer and more widespread episodes – such as the January 2005 Carlisle floods, the summer of 2007, the November 2009 Cumbria floods, the April and June 2012 and November 2012 floods, and then the stormy winter of 2013/14. It was distressing for Cumbrian communities that the 2015 floods were so severe after new defences were built only recently (following the November 2009 floods). There was repeated exceedance of rainfall records and high return periods (e.g. > 1 in 1000 year events in 2009 and 2015). For example, the peak levels reached in some rivers in Yorkshire (such as the Aire and the Wharfe) were up to a metre higher than previous records.
This poses numerous questions. Here are just a few.
Firstly, does the temporal clustering of such large extremes (in what seems unusual sequences) predominantly further the argument for the effects of climate change (and alter pre-existing statistical assumptions behind anticipated weather extremes), or just show how we have a lack of data to define these extreme events? Researchers who have analysed palaeoflood deposits in UK uplands note that the term ‘unprecedented’ should not be coined so readily when extreme events are being characterised using relatively short (less than half a century) data sets (e.g. of flow records). This is certianly a rational view especially when also considering how both landscape and climate are changing.
So, secondly, should we radically re-evaluate how data, modelling and statistics are used in the management of floods? Thirdly, what (realistically) are the implications of so many extreme floods in such a short period of time, for government funding of flood protection and recovery? Albeit an obvious statement, recent events highlight the uncertainty of what we can expect from future floods, including the uncertainty in which responses will be most effective.
Some further reading (also see links in article)
Lavers, D.A., Allan, R.P., Villarini, G., Lloyd-Hughes, B., Brayshaw, D.J. and Wade, A.J., 2013. Future changes in atmospheric rivers and their implications for winter flooding in Britain. Environmental Research Letters, 8(3), p.034010.
Joint Defra/EA Flood and Coastal Erosion Risk Management R&D Programme, 2004. Review of impacts of rural land use and management on flood generation: Impact study report. R&D Technical Report FD2114/TRP.E. Authors: O’Connell, K. J. Beven, J. N. Carney, R. O. Clements, J. Ewen, H. Fowler, G. L. Harris, J. Hollis, J. Morris, G. M. O’Donnell, J. C. Packman, A. Parkin, P. F. Quinn, S. C. Rose M. Shepherd and S. Tellier. November 2004.
Houses of Parliament – Parliamentary Office of Science and Technology, 2011. Natural Flood Management. POSTNOTE Number 396 December 2011.
O’Connell PE, O’Donnell G. 2014. Towards modelling flood protection investment as a coupled human and natural system. Hydrology and Earth System Sciences 2014, 18(1), 155-171.
University of Cambridge, 2016. ‘Unprecedented’ storms and floods are more common than we think – See more at: http://www.cam.ac.uk/research/news/unprecedented-storms-and-floods-are-more-common-than-we-think#sthash.NspnM59G.dpuf