A LOOK BACK PART 2: UK Summer Floods 2012 & Comparison To 2007

I believe the 2007 and 2012 washout summers was down to the combination both the peaking of the warm Atlantic Multidecadal Oscillation and very warm North Atlantic including waters surrounding the British Isles and the onset of an El Nino.

SSTA’s at the beginning of April 2007 and 2012 where exceptionally warm.

anomnight_4_3_2007

anomnight_4_2_2012

Record rainfall – April to July 2012

From Met Office

From April to July 2012 the UK experienced a period of exceptionally wet weather, breaking previous rainfall records and resulting in several significant flood events.

The wet weather affected all of England, Wales and eastern Scotland. April, June, and the period April to July were each the wettest on record in the England & Wales precipitation series from 1766, while for the UK overall, summer 2012 (June, July and August) was the wettest since 1912. The record rainfall brought the 2010-12 England and Wales drought to an abrupt end. In contrast to the wet weather elsewhere, the far north-west of Scotland saw well below-average rainfall from March to October 2012.

The persistent wet weather was due to a shift in the jet stream to a much more southerly track than normal, bringing a succession of Atlantic low pressure systems and associated fronts across the southern half of the UK.

Impacts

After the drought, the wet weather was initially very welcome, bringing much-needed rain for farmers and growers. However, before long it brought new problems.

Waterlogging made access to land difficult, reduced yields and caused some crops to rot. Various flood incidents through the period caused widespread problems, particularly to the transport network. Surface water flooding and debris closed main roads. Railway lines were blocked by flooding and landslips. Birmingham airport diverted inbound flights in late June.

Landslides and cliff collapses affected the south-west coast, with one fatality. Areas of West Yorkshire were affected by flash flooding from the River Calder three times in two weeks during June and July. Evacuations of properties and caravan parks were necessary in Wales, Yorkshire and eastern Scotland.

Leisure activities were affected – for example festival-goers on the Isle of Wight were stranded due to heavy rain and waterlogged ground, though the Olympic Torch relay persisted in spite of bad weather. The flooding also brought ecological problems – unseasonable flooding of wetlands destroyed nests of ground-nesting birds (e.g. in the Ouse Washes) and receding flood waters stranded fish.

The wet spell was punctuated by numerous high rainfall totals causing flooding problems. Notable one-day accumulations included 101 mm at Chilgrove House, West Sussex on 10 June and 208 mm at Honister Pass, Cumbria on 22 June. Two-day accumulations included 186 mm at Rheidol, Aberystwyth on 8 to 9 June, 145 mm at Bognor Regis, West Sussex on 10 to 11 June and 132 mm at Charminster, Dorset on 6 to 7 July. Many of the flood incidents were localised in nature and due to torrential downpours, which overwhelmed drainage systems and caused flash flooding. While several thousand properties flooded, the flooding was not on the scale of summer 2007, when over 55,000 properties were flooded across England and Wales. One reason was the benefit of the network of flood defences across the UK; without this, many more properties would have been affected. In summer 2007 there was large scale fluvial flooding, less spatially extensive but much more damaging overall.

The persistent wet weather transformed the UK’s water resource situation. In particular, it allowed groundwater levels to recover in the chalk aquifers of south-east England (an important water resource); this is extremely unusual at this time of year.

In stark contrast, parts of north-west Scotland suffered drought stress through summer 2012. Wildfires threatened historic buildings in Stornoway, there were reports of springs drying up and whisky production was interrupted on Islay, Mull and Skye.

Weather data

The months of April and June were exceptionally wet, with most parts of England, Wales and eastern Scotland receiving two to three times the monthly average rainfall widely – approaching four times in a few locations. Remarkably, April and June were each the wettest such months in both the UK series from 1910, and the England & Wales precipitation series from 1766.

The following maps show rainfall for April and June 2012.

Rainfall percent of average map for April 2012 Rainfall percent of average map for April 2012

Rainfall percent of average map for June 2012 Rainfall percent of average map for June 2012

Perhaps the most dramatic day during the spell of wet weather was 28 June 2012. Two lines of intense thunderstorms tracked across England; one from the West Midlands to Lincolnshire, the other from Morecambe Bay to north-east England. These brought torrential downpours, hailstones large enough to damage greenhouses and cars, and intense lightning activity (over 50,000 strikes were recorded across the UK through the day). The Newcastle-on-Tyne area was particularly badly affected by flash flooding; rainfall rates of 20 to over 30 mm per hour were widely recorded.

The following map shows lightning strikes for 28 June 2012

Lightning strikes 28 June 2012 Lightning strikes 28 June 2012

The wet weather continued to predominate for the first two-thirds of July. Many parts of England, Wales and southern Scotland received more than twice the average rainfall for the month overall. Rainfall for the April to July period approached twice the average widely across England, Wales and eastern Scotland and this period was the wettest in the series from 1910 for the UK overall. It was also the wettest such period in the England & Wales precipitation series from 1766.

The following map shows rainfall totals for the period April to July 2012. (The area of ‘Lowland England’ is shown in bold; in this area, groundwater – mainly from chalk aquifers – is an important water resource).

Rainfall percent of average map for April to July 2012 Rainfall percent of average map for April to July 2012

Rainfall totals for the period April to July 2012 are given in Table 1 below.

Rainfall totals for the period April to July 2012
Region April to July rainfall (mm) % of 1981-2010 average Rank (series from 1910) Highest or previous highest since 1910
UK 462 157 1 414 mm – 1931
England 452 187 1 389 mm – 2007
Wales 598 169 2 614 mm – 1920
Scotland 449 123 5 503 mm – 1947
Northern Ireland 416 136 6 462 mm – 2002
England & Wales 472 184 1 408 mm – 2007
England N 488 181 1 423 mm – 2007
England S 433 191 1 371 mm – 2007
Scotland E 486 159 1 450 mm – 1916
England E & NE 441 188 1 383 mm – 2007
England NW & N Wales 553 168 2 555 mm – 1920
Midlands 457 190 1 433 mm – 2007
East Anglia 367 186 1 293 mm – 2007
England SW & S Wales 561 181 1 487 mm – 1920
England SE & Central S 417 198 1 350 mm – 1924

August continued largely wetter than average – particularly across south-west England. For UK overall, the summer of 2012 was the wettest for a century (since 1912).

The following map shows rainfall totals for summer 2012.

Rainfall percent of average map for summer 2012 Rainfall percent of average map for summer 2012

Monthly rainfall anomalies for the area of Lowland England (defined by the bold line on the April to July rainfall map) are given in the bar chart below. The exceptionally wet weather from April 2012 onwards brought the 2010-2012 drought to an abrupt end.

Monthly rainfall (% of 1981-2010 average) for Lowland England 2010 to August 2012 Monthly rainfall (% of 1981-2010 average) for Lowland England 2010 to August 2012

The 2010-2012 England and Wales drought and other noteworthy weather events are described from the index page.

Further hydrological information is available from the following links to the Environment Agency and Centre for Ecology and Hydrology, Wallingford.

Environment Agency Water Situation Reports

Centre for Ecology and Hydrology Monthly Hydrological Summaries

The Met Office is not responsible for the content of external internet sites

For a description of monthly summaries, including rainfall statistics from April 2012 onwards, please refer to the UK climate summaries.

For a more detailed summary of the 2012 transformation from drought to floods, refer to the following publication:

Parry S. Marsh T, Kendon M. 2013. 2012: from drought to floods in England & Wales. Weather 68: 268-274.

Last updated: 3 October 2013

Summer Floods in the UK: Comparing 2012 and 2007

Article from AIR WORLDWIDE

Editor’s Note: Senior Client Services Associate Thomas Hughes, from AIR’s London Office, and Science Writer Sara Gambrill compare the UK summer floods of 2007 and 2012 and what the future may hold for the UK in terms of flood defense and insurance coverage.

Rain fell in record amounts in the UK from May through July 2007, causing major flooding in late June and again less than a month later. Insured losses totaled about GBP 3 billion. As it turned out, the 2007 floods were the perfect dress rehearsal for the record-breaking rain that would fall on the UK in 2012. In particular, June 2012 walloped the June 2007 rainfall record, that itself had broken the previous record that had stood for nearly 40 years.

But, interestingly, summer 2012 was no repeat of summer 2007. While both experienced a similar jet stream position and record-breaking rainfall, differences include: precipitation patterns and timing; the weather and related soil conditions preceding the record-breaking rainfalls; flood defenses; and insured losses.

The Summer of Flood: 2007

In 2007, the UK experienced its wettest June since detailed record-keeping began in 1914. According to the UK Met Office, 136.2 mm of rain fell across the UK that month, nearly twice the normal amount. The flooding, which began on Monday, June 25, continued throughout the week and was exacerbated by heavy rain earlier in the month that set the stage with wet soil conditions and elevated water levels. The ground was saturated by mid-June, and many reservoirs that would normally have had capacity to absorb runoff were full. In addition, paved surfaces in urban areas behaved like saturated soil and contributed to surface water flooding. What was unusual in 2007 was for how many days the rain fell. Flooding started again on July 21 and again continued for a week.

The Jet Stream’s Unusual Position

Some of the blame for the UK 2007 floods rests with the unusual position of the jet stream during that time. The jet stream, a conveyor belt of fast moving air 36,000 feet above the earth, controls the movements of extratropical cyclones. Normally, the jet stream lies across the Northern Atlantic during the summer months, allowing the UK some respite from the cloudy, wet weather that characterizes much of the year (see Figure 1).

 The article: Describes the difference in impact of the 2007 and 2012 floods in terms of timing, flood defenses and insured losses.
Cat Bond Figure 1 Event 1
Figure 1. During a “normal” summer, the jet stream directs areas of low pressure to the north of the UK, but during the summer of 2007, it flowed farther south, allowing low pressure systems to travel over the heart of the UK (Source: AIR Worldwide)

But for much of the summer of 2007, the jet stream was positioned several hundred miles south of its usual position, bringing unusually heavy rain to the UK (see Figure 1). The Met Office stated that the amount of rainfall may have been exacerbated by warmer-than-normal sea surface temperatures (SSTs) around the UK during the preceding winter and spring. Higher SSTs result in increased evaporation, putting more moisture into the atmosphere which, in turn, can fall as rain.

Surface Water Flooding’s Role in Damage and Loss

In its Review of 2007 summer floods, the Environment Agency stated that the 2007 floods were different in scale and type from other severe floods in the recent past. Specifically, a much higher proportion of flooding came from surface water rather than rivers. Two thirds of the 55,000 properties, or roughly 35,000 homes and businesses, flooded because drains and sewers were overwhelmed. Roughly 19,000 homes on floodplains were inundated by overflowing rivers. Of those, 3,600 were flooded when existing flood defenses were overwhelmed. The agency estimated, however, that a further 100,000 properties had been protected by artificially constructed defenses. Insured losses totaled about GBP 3 billion.

Although the Environment Agency issued 500 flood and severe flood warnings during the summer—80% of which the agency believes gave two hours’ notice of flooding—the warnings only apply to flooding from major rivers; the agency’s flood warning service does not issue warnings for surface flooding, or risk of flooding from sewers, drains, groundwater, or ditches. Many properties, according to the Environment Agency, were flooded twice—first by surface water, then by river water—so they received flood warnings only after they had already been inundated.

Cat Bond Figure 1 Event 1
Figure 2. AIR damage survey, July 9, 2007, Central Toll Bar, Yorkshire
Cat Bond Figure 1 Event 1
Figure 3. AIR damage survey, July 9, 2007, Toll Bar floodplain

The Environment Agency stated in its 2007 review that “surface water flooding problems are likely to increase with development pressures, climate change, and aging infrastructure.” In the metropolis of London alone, surface water was responsible for flooding virtually all the 1,400 properties affected.

Flood After Drought: 2012’s Water Resource Turnabout

The two dry winters of 2011 and 2012 led to drought conditions across the UK, causing major roads to crack and reservoirs to hit their lowest recorded levels. On April 5, 2012, a “hosepipe ban” went into effect for 20 million people getting their water supply through the main water system, which meant that they were forbidden to use their garden hoses for most domestic purposes, such as washing a car, watering plants, or filling a backyard pool.

Then the rain began. The UK received a total of 126.5 mm of precipitation in April, more than double the rainfall for that month compared to the 1971-2000 average. It was the wettest April ever recorded. June 2012 also saw a record-breaking amount of rainfall over the UK—145.3 mm, exactly double the average. The wettest April to June period in the UK’s history brought near total recovery from the drought by mid-July. Reservoirs became full or exceptionally high, and river levels tripled. Such a widespread and sustained recovery from drought had never been seen in the UK before, according to the Centre for Ecology & Hydrology.

The UK government had to turn on a dime from focusing on drought conditions in April to the risk of flooding in May, which persisted well into autumn. Between May and mid-October, the Environment Agency sent 100,000 direct warnings to households and businesses. UK insurers estimated by mid-July that their losses from June 2012 alone would reach GBP 500 million but posited that total costs would not exceed the costs of the 2007 floods. Through mid-October, 4,500 properties had been flooded in 2012 in the UK. The Environment Agency, Met Office, and Centre for Ecology & Hydrology have all warned that the UK must plan for swings between drought conditions and flooding periodically from now on.

“Futuristic” Flood Defenses Mitigate Losses

Although the position of the jet stream during the summer of 2012 was similar to that in 2007, there were a number of factors that prevented the 2012 floods from incurring the level of insured losses that 2007 did. One is that the record-breaking rainfall in 2012 followed a long period of drought, so the soil was not already saturated as it was in 2007. Also, there were periods of relief even during the record-breaking April-June period; the second half of May was relatively dry, and there were other periods of respite between the rain, which lessened the impact. The other, more important, differences were the increase in the number of flood defenses—190,000 more properties were protected in 2012—and the innovative types of flood defenses installed and implemented between the floods of 2007 and 2012.

Innovations in flood defense comprise a wide range of solutions, including upgrades to the warning system. The Flood Forecasting Centre, which is a joint Environment Agency and Met Office team, has significantly improved the lead time and accuracy of its flood forecasts, giving more notice and better information to emergency responders, infrastructure operators, and homeowners. In addition, the Environment Agency has added new online and social media applications, including Facebook Flood Alerts and Flood Alert apps for mobile devices, to their already existing flood warning communication channels of telephone, email and text messaging. In addition, map developers Shoothill have created live online flood mapping solutions that are directly linked to the Environment Agency’s flood warning system to help users visualize what areas are under threat of flooding.

Cat Bond Figure 1 Event 1
Figure 4. A glass wall flood defense in Keswick, Cumbria (Source: ITV)

Other improvements in flood defense are a result of engineering innovations. Three examples follow. A flood defense that uses self-raising gates—a first for the UK—is being installed in Cockermouth, in Cumbria, which was flooded three years ago. The self-closing gates use the floodwater’s power to raise the barriers and hold them in place. As the flood waters recede, the gates slowly descend. Another type of defense is the glass flood defense, used instead of a reinforced concrete defense to preserve the view. Keswick, also flooded in 2009, has just had a glass flood defense installed. And finally, in places like the village of Belford in Northumberland that experience frequent flooding when rain runs off nearby farmland, a combination of ponds to store floodwater and planted woodland to slow the flow of water have been installed—relatively cheap and effective ways to protect against flooding.

Paul Mustow, the Head of Flood Management at the Environment Agency, claims that 53,000 properties would have been flooded in 2012 without flood defenses—very close to the number that were actually flooded in 2007—and that 190,000 received flood protection during the intervening years. He also stated that flood defenses repaid their investment by a factor of 8-1 but that continuing to invest in them would be challenging, given government cuts to the budget.

Flood Defense Budget’s Ups and Downs

The annual capital budget for flood defense doubled to GBP 600 million during the decade preceding 2007 and then increased by 33% between 2007 and 2010 to GBP 800 million. However, in 2010, the Environment Secretary offered to cut 30% from the Department for Environment, Food and Rural Affairs (DEFRA) budget in the interest of helping to cut the government’s overall budget deficit. The Secretary’s offer was accepted despite the fact that after the floods of 2007, The Pitt Review: Learning lessons from the 2007 floods stated unequivocally that the government needed to “ensure proper resourcing of flood resilience measures, with above inflation increases every spending review.” The cut to DEFRA’s spending translates to a cut in capital spending, mostly on flood defenses, from GBP 600 million per year to GBP 400 million per year during the four-year period from 2011-2015. Flood spending overall will total GBP 2 billion during the same four-year period, representing a cut of 20 to 30%.

The Future of Flood Insurance in the UK

Currently in the UK, flood insurance is made available to all under the “statement of principles” (see sidebar), which aims to provide affordable, near universal flood coverage. This system involves cross-subsidization of premiums from households in low-threat regions to households in high-threat regions. The statement of principles is due to expire in June 2013, leaving the future of flood insurance in the UK uncertain.

A number of brokers have already begun working on solutions in the form of UK flood pools. In addition, both the Association of British Insurers (ABI) and the British Insurance Brokers Association (BIBA)—lobbying arms of the insurance and insurance broking interests in the UK, respectively—are working with the government to develop a strategy for replacing the statement of principles, which would lead to a more objective risk-based system. If insurance companies were allowed to charge premium based on real risk to the property, in the long term it could arguably discourage construction in flood-prone areas; however, in the short term, a shift to this type of open system, without provision for people already living in flood-prone regions, would lead to hardship for some.

The ABI has estimated that if the statement of principles were to expire without contingencies in place, up to 200,000 households would struggle to obtain flood insurance at affordable rates. Thus, the likelihood of the creation of a government subsidized pool to help maintain affordable insurance in highly flood-prone regions seems to be quite high.

Flood is now the top natural hazard that the UK faces. The risk of flooding already threatens 5 million homes in the UK, and it is thought by UK government officials that climate change will increase that number. It remains to be seen whether innovations in flood defense and the insurance landscape in the UK will serve to increase the UK’s resilience to flood hazard in the years to come.

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