The floods of December 2015 in northern England: description of the events and possible implications for flood hydrology in the UK

Abstract

In December 2015, northern England experienced two major flooding events with extreme, even in some locations unprecedented, rainfalls and flooding. New 24-, 36-, and 48-hour UK rainfall records were created of 341.4, 401.4, and 405.2 mm, respectively. Three river-flow gauging stations, with flows of around 1,700 m3/s exceeded the previous peak flow record for England and Wales. There was widespread flooding, including major towns and cities, some of which had recent flood alleviation schemes. In Cumbria, the flood events in 2005, 2009 and 2015 compared with previous and historical events raise questions about the stationarity of the flood data and flood-producing mechanisms. These possible effects are less apparent elsewhere in northern England. This paper discusses whether present methods of estimating flood risk are able to cope with such extreme events and suggests topics for future research. In the meantime, for studies where flood estimates are important, practical hydrologists are faced with the difficult task of producing design flood estimates which fit with our understanding of these events.

Can we still predict the future from the past? Implementing non‐stationary flood frequency analysis in the UK

“…Following the floods of December 2015, the Environment Agency commissioned a hydrological review (summarised by Spencer et al, ). One of the outcomes was a decision to carry out trend tests and to trial non‐stationary flood frequency analysis at a set of 33 gauging stations in north‐west England.…”

“…North‐west England has been particularly badly hit, with severe floods in 2005 (Carlisle), 2009 (much of Cumbria), and 2015 (much of Cumbria and Lancashire). Flood walls built after the first two events were overtopped in 2015 (Spencer et al, ). People who are affected by such events can understandably be sceptical that two or even three extreme floods have occurred purely by chance so close together.…”

Convergent human and climate forcing of late-Holocene flooding in northwest England

“…Meteorological patterns in northwest England are largely driven by moisture-laden westerly zonal air masses, owing to the maritime setting (Burt and Ferranti, 2012). Westerly and south-westerly cyclonic systems have been linked to regional 21 st -century floods (Spencer et al, 2017) and earlier historical extreme events (Pattison and Lane, 2012) and their formation appears correlated with the winter North Atlantic Oscillation (wNAO) Index (Jones et al, 1997;Wilby et al, 1997). The NAO appears to exert some control over the timing and duration of regional wet phases (Fowler and Kilsby, 2002;Pattison and Lane, 2012) but linkages between both positive and negative NAO phases and high flows in Britain (Foulds and Macklin, 2016;Hannaford and Marsh, 2008) emphasise its complexity as a flood generating mechanism.…”

Convergent human and climate forcing of late-Holocene flooding in Northwest England

“…Floods in 2005(Environment Agency, 2006 and 2009 (Eden and Burt, 2010;Miller et al, 2013;Sibley, 2009) had similarscale impacts and pooled peak flow return periods for the River Eamont (downstream of Brotherswater) were revised downwards by an order of magnitude (5877 to 460 years ;Miller et al 2013). Re-assessment after Storm Desmond (December 2015) further reduced this estimate to 350 years (Spencer et al, 2017). Longer hydrological time series that capture greater numbers of extreme floods are clearly needed to contextualise regional flood frequency estimates.…”