UK Boxing Day Floods

First Posting | Summary
Posting Date: December 29, 2015, 11:00:00 AM

Storm Eva brought severe flooding to northern UK on Boxing Day—the day after Christmas—when record-breaking rains fell on already saturated areas. Parts of northern England, including parts of Manchester, Leeds, and Lancashire, were submerged by up to 1.8 m of water after a month’s rain fell in a single day in some areas. Environment secretary Liz Truss stated that, “Every single river was at a record high,” and some rivers had reached levels exceeding historical records by one meter. During the event, a total of 21 severe flood warnings, 227 warnings, and 138 alerts were issued across England and Wales, and 16 flood warnings and three alerts were issued for parts of Scotland.

Figure 1. MODIS satellite image of Storm Eva on December 27, 2015. (Source: NASA)

Meteorological Summary

Just three weeks after Storm Desmond, Storm Eva―the second major storm and fifth named storm of the European winter storm season―moved into the region on Saturday, December 26, 2015, with drenching rains. Peak sustained winds of 65 km/h with gusts as high as 120 km/h were recorded, and rainfall totals of 50−80 mm fell over just 6−9 hours on soil still saturated from Desmond and already elevated water levels. The highest rainfall totals from Storm Eva were around 100 mm, with peaks of 130 mm in Lancashire and in excess of 200 mm in Snowdonia.

Figure 2. Map showing rainfall totals from Christmas Day to Boxing Day. (Source: Met Office; Contains public sector information licensed under the Open Government Licence v1.0)

Prior systems throughout the month of December left much of the region already at more than double their average December rainfall totals. The Met Office confirmed that this will be the wettest December on record since 1910 for Cumbria, where areas have experienced more than two and a half times the expected monthly rainfall. Red warnings were issued by the Met Office in Lancashire, and Yorkshire and the Humber, indicating danger to life, expected property damage, and a need for immediate action. This marks the first time two such alerts were issued in one day. Amber and yellow warnings were issued for parts of Lancashire, Cumbria, northern Wales, and parts of Scotland.

These regions were among the hardest hit by Storm Desmond about three weeks prior, and the overall saturated soil conditions in the region elevated flood risk due to heavy rainfall from Storm Eva. Final December rainfall totals ranged from 280−770 mm in Cumbria, and from 240−330 mm in the Lancashire and West Yorskhire regions. Record-breaking December rainfall totals were also seen in Wales, where Conwy reported 1009 mm; the previous record was 613 mm.

Figure 3. December rainfall totals for the UK prior to the Boxing Day floods, highlighting the already saturated soil conditions across the region. (Source: Met Office; Contains public sector information licensed under the Open Government Licence v1.0)

River level records were broken around the region. Water levels in the Ribble river at Ribchester reached their highest levels ever recorded at 5.91 m at 3 p.m. on December 26; the level of the Calder river at Hebden Bridge peaked at 3.63 m on December 26, passing its previous record of 3.3 m; the River Aire at Armley exceeded its previous record of 4.03 m on December 27 when waters reached more than 5 m; the former record of 2.44 m in York at Tang Hall was surpassed when waters reached 4.62 m on December 27; and the River Ouse’s water level at Viking Recorder approached its highest record of 5.4 m from November 2000 when it reached 5.19 m on December 28. Although many river levels peaked by Monday afternoon, more rain was expected in southwestern England and southern Wales on Monday afternoon and northern Wales and northwestern England Monday evening, albeit at lesser amounts than those seen on Boxing Day. 

Reported Impacts

Thousands of homes and business have suffered significant damage from flooding due to heavy precipitation and rising rivers. Evacuations were ordered in multiple areas, and British armed forces were dispatched to join fire and police teams to provide disaster assistance. In Lancashire alone, 350 incidents and 50 rescues were reported on Boxing Day. In Leeds, 12,000 were without power and 1,000 homes were affected. Power was cut to 10,000 homes in Rochdale and Lancashire when floodwaters hit a main substation, and another 3,000 homes in North and West Yorkshire were also without power.

More than 300 flood-related calls were reported in Greater Manchester. Flooding contributed to a gas explosion in Radcliffe in Greater Manchester at around 4:30 p.m. on Boxing Day, caused by a ruptured gas main, which also caused a footbridge collapse. Road closures were expansive, including a number in the wider Manchester metropolitan area, where the Bolton, Bury, Rochdale and Oldham areas were most affected.  

Flooded streets turned into urban rivers, sinkholes were reported, travel was disrupted, and some regions were completely isolated. Northwest Wales was effectively cut off by flooding when its two major arteries were shut down due to rising waters. Todmorden, in Calderdale, was also completely cut off, impeding emergency services. Many tourist attractions were shut down and events were cancelled due to flooded roadways, including a number in York―the city worst hit by the Boxing Day floods.

Flood Defense Failure

Flood defenses were breached along the Calder, Ribble, Nidd, Irwell, Ouse, Foss, and Aire rivers, all of which burst their banks, leading to questions being raised about flood defense spending and mitigation efforts. About 85% of the Britain’s temporary flood defenses were sent to Cumbria after Storm Desmond, and many residents reported a lack of available defenses during the Boxing Day floods. In York, a decision to raise a flood barrier for fear of water overtaking it and compromising its electrical functionality is being highly debated, with specific questions aimed at upkeep and design. The 4 km of flood defenses around York, constructed between 1985 and 1995, were built to withstand river levels of up to 5.45 m above normal summer levels and have never been breached.

Figure 4. The River Aire bursting its banks and the adjacent house at risk. (Source: Rich Tea)

Prime Minister David Cameron told Sky News that flood defenses do not “always do enough.” Though there has been criticism of a north-south divide in flood defense spending, Cameron has said that more was spent per head in the north than the south. A EUR 2.3 billion plan exists to improve flood defenses over the next six years. Environmental Agency Deputy Chief Executive David Rooke expressed a need to rethink flood defense and mitigation. Rooke acknowledged the unprecedented extremes of recent storms, and voiced an interest in proactive engineering, construction, and warning systems for enhanced flood resilience. 

Exposure at Risk

Most of the residential buildings in this region are detached, semi-detached, or terraced (row) houses and are primarily of masonry construction. Light metal is often used for low-rise storage buildings. When low-rise buildings such as single family homes are flooded, a significant percentage of the building, and its contents, will sustain damage; however, the damage is usually limited to the cellars. The presence of a cellar also increases the risk for contents damage, particularly in the case of heavily-used cellars that enclose recreational rooms, bedrooms, or home offices. Some homes may have entire apartments located in the cellar as well. However, heavily-used cellars usually have better flood defense mechanisms than unfinished ones.

Commercial building stock uses a wider variety of materials, including masonry, reinforced concrete, or steel. Commercial buildings are usually built to stricter standards under the supervision of an engineer and therefore usually have sophisticated flood defenses in place, particularly in zones with a lower return period for flood. However, post-disaster surveys indicate that low-rise commercial wood frame and masonry buildings are generally non-engineered and have vulnerabilities similar to those of their residential counterparts. Large apartment and condominium buildings frequently receive a degree of engineering attention similar to that given to engineered commercial construction, reducing their vulnerability.

Insurance Impact

Loss estimates from the Boxing Day floods will continue to form over the next few days as water levels recede and companies can enter properties and assess damage, though economists submit that the impact could hinder Britain’s economic growth by 0.2%. Damage from Storm Desmond has been estimated at more than EUR 520 million by the Association of British Insurers (ABI), and some early projections for damage from Storm Eva are higher due to the greater number of areas and businesses affected and poor conditions left by Storm Desmond at the time of occurrence. York, which was the hardest hit by flooding after the River Foss broke its barriers, is likely to represent a significant proportion of the upcoming insurance claims.

In the UK, flood coverage is included in standard policies under an evolving informal public-private partnership, whereby the industry agrees to provide affordable insurance while the government invests in flood defenses. Requests for emergency insurance payments are expected to be high; ABI reported emergency insurance payments totaling EUR 2.6 million after Storm Desmond.

Storm Frank

On the heels of Storm Eva looms Storm Frank, set to bring more rain and gale-force winds to parts of northern and western UK on Wednesday. Met Office yellow rain warnings have already been issued for northwestern England, northeastern England, Yorkshire and Humber, Wales, and Northern Ireland. Rainfall totals of 20−40 mm are expected, with 60−80 mm possible in some areas. Amber rain warnings have been issued for Cumbria and parts of central and southern Scotland, where 100−120 mm of rainfall may be seen. There were 57 flood warnings as of 7 p.m. on December 28, 2015, including nine severe flood warnings and 48 flood warnings, and another 64 flood alerts.

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Posting Date: December 29, 2015, 11:00:00 AM