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JBA and Met Office November 2012 UK Floods

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The Background

Throughout the last ten days of November alone, the North East Midlands and South West of England experienced above the average rainfall expected for the entire month. Following on from the second wettest summer since records began, the precipitation was falling on already saturated ground, leading to widespread flooding across many parts of the country.

A mass evacuation of around 1,000 people took place in Northamptonshire with many hundreds being evacuated from other towns and villages elsewhere around the country. Meetings at the racecourses in Southwell and Sedgefield also had to be cancelled. So far, four people have been killed and over 1400 homes affected, with cleanup operations expected to be troubled by a cold December.

A Mini Cooper struggles in the rising waters in St. Asaph, North Wales. Photograph courtesy of Rob Davidivitz (@RobDavSky)

Insurance impacts  

The cost to insurers of the recent and ongoing floods in the UK is still being assessed, but one estimate for the year as a whole, including the floods earlier in the year, stands at £1 billion, considerably lower than the £3 billion of 2007. In the coming weeks, questions will be raised over the future of flood insurance in the UK and perhaps regarding the responsibility of developers and land marketers. In cases such as the Glasdir estate in Ruthin, North Wales, homeowners were surprised to discover that the new development had been built on a floodplain. The Lincolnshire village of Swaton has flooded four times this year; once in July and three times in November. In previous years, insurers have had an agreement with the UK government that flood cover should be included on policies as standard, in exchange for the public-sector building and upkeep of defences. With the end of this agreement looming in July of next year, insured parties face concerns that they might be unable to secure flood insurance for their homes in future.

For England and Wales, the 7-day period from 20 to 26 November was provisionally the second wettest week in the last 50 years, behind only a spell from late October to early November 2000. Over this period, most of England and Wales recorded over 75mm of rainfall, a large swathe from south-west England through the Midlands and Wales to northern England over 100mm, and over 150mm was recorded in some locations. These accumulations were due to successive low pressure systems and associated fronts affectingEngland and Wales on 20-21, 22, 24-25 and 26 November 2012. Parts of southern Scotland (particularly the Glasgow area) had also recorded around 50mm on 18 November which caused some flooding problems; Scotland, however, escaped the subsequent wet weather. The resulting flooding was exacerbated by already very wet ground conditions following the exceptionally wet weather from April to July 2012. August and October were also wetter than average in many parts.

19-26 Nov 2012 7-day rainfall: left: recorded rainfall (mm); right: % of average all-November total

Meteorology: first intense episode (20-21 Nov)

Prolonged heavy rain fell across much of south-west England overnight between 20 and 21 November 2012 from a front associated with an area of low pressure. Around 40 to 50mm fell across a 12-hour period: while notably wet, not exceptional. However, with the ground already saturated, there were widespread flooding problems, particularly to transport routes with road floods and landslips. Rainfall totals at Exeter and Dunkeswell (Devon) were recorded at over 40mm in the 12 hours from 2200 to 1000.  The frontal system included some lines of more intense rainfall and heavier bursts which are most likely to have caused the flash-flooding.

Meteorology: further rain, strong winds (22 Nov)

A particularly active cold front brought further heavy rain sweeping across the UK during 22 November. The rainfall radar imagery for 16:00 on 22 November, shows an unusual and distinct line of intense rainfall from south Cornwall to the Scottish borders. Although again the overall totals were not exceptional, the rain fell on already saturated ground and included some short, very intense bursts. Much of south-west England recorded a further 20mm of rainfall, while parts of North Wales and Cumbria recorded around 40mm. There were further widespread flooding problems and travel disruption occurred across the South West, the Midlands, Wales, Cumbria and Scotland. The passage of the front was accompanied by very strong winds, gusting at 46 to 58 mph widely across inland locations, and up to 70mph in exposed coastal locations. Maximum gusts included 86mph at Capel Curig, Gwynedd, 70 mph at St Marys, Isles of Scilly, and 68 mph at Emley Moor, West Yorkshire.

Meteorology: heavy rain, strong winds (24-25 Nov)

After a brief respite, with lighter winds and, in many areas, an early-morning frost, another low-pressure area moved up from the south-west on Saturday 24. Rain persisted all day across much of southern England, and pushed up into the Midlands and north-east England through the day. More than 50mm fell widely, and with the ground already saturated there were major flooding problems. Devon and Cornwall were among the worst-hit areas, but there were problems elsewhere too. The system brought very strong winds in its wake, gusting at around 46 to 58 mph across south-east England. Showers followed on Sunday 25, which merged into longer spells of rain in places as another, albeit less vigorous, depression moved in from the west. By 0900 on Monday 26, many places along a line from Devon to Humberside had had over a month's worth of rain in the space of a week.

Meteorology: final heavy rains (26 Nov)

Arriving quickly after the previous system, the next system brought lighter, more showery rain across the worst-hit areas of south-west England but more persistent, heavy rainfall across much of northern England and north Wales from late on Sunday 25. Around 30 to 50mm of rain was recorded in these areas; as before, not exceptional totals in themselves, but causing further significant flooding problems on top of all the previous rainfall.

Rainfall charts provided by National Climate Information Centre, background maps © Crown copyright.
All diagrams © Met Office 2012.

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