The floods of Summer 2007: 10 years on

Whilst the UK has been enjoying very hot temperatures recently, 10 years ago it was a different story.

The Summer of 2007 was the wettest since rainfall records began in 1766.  Heavy rain triggered two extreme rainfall events; on 25th June and again on July 20th.  The Met Office reported that from May through to July 2007 more than 387mm of rain fell across England and Wales which is double the average for the period. Despite a relatively dry April, by mid-June the ground was saturated and low sunshine levels meant that there was little evaporation.

On 25th June, intense rainfall led to severe flooding in parts of the North East including Sheffield, Doncaster and Hull; areas in which the level of penetration of insurance is low compared to other parts of the UK.  In Hull, over 6,000 properties were flooded and more than 10,500 homes evacuated as flash flooding led to drainage and sewage systems being overwhelmed.  The flooding caused major disruption to homes and businesses with almost half a million people without a water supply for up to 3 weeks and left many residents unable to return to their homes for up to a year.

More heavy rain on July 20th caused flooding in many parts of England and Wales with some areas hit particularly bad such as Gloucestershire, Cambridgeshire, Wiltshire, Hampshire and Oxfordshire where properties were flooded for the second time in less than a month.

 The impact on the insurance industry

The Environment Agency (EA) estimated the total costs of the 2007 floods to be £4 billion.  Around £3 billion of this loss was covered by insurance, making this one of the costliest events to date for the UK insurance industry.   In terms of insurance claims, the ABI reported around 165,000 claims with 132,000 of those claims for damage to domestic households.   Thankfully this was a rare event and believed to be somewhere between a one in 500 years and a one in a 1000 years event. This estimate though is very much a guess given the amount of data used to base this estimate on and with a changing climate calling into question the assumptions underpinning the analysis.

How flood risk mapping has changed since 2007

Whilst it is not unusual for the UK to experience extreme rainfall in the Summer, a much higher proportion of the flooding of Summer of 2007 was due to surface water flooding rather than any other type of flood risk (e.g. river flooding). By its very nature, surface water flooding is very localised and is caused by large volumes of rain water, making it very difficult to accurately predict exactly where flooding will occur geographically.

At the time, there were no surface water flood maps and insurers did not factor it into their ratings.  Today over 3 million properties are estimated to be at risk of surface water flooding in the UK.

Following the 2007 floods, the Pitt Review found that work was needed to improve the management of flooding from surface water and poor drainage.  It also identified the need for surface water flood maps for England and Wales. Subsequently, JBA Consulting developed the first nationally produced model of surface water flooding to supply to the EA.

The Flood Map for Surface Water (FMfSW) in England and Wales was developed in 2009 and included:

  • an additional rainfall probability
  • the influence of buildings
  • reduction of effective rainfall through taking account of drainage and infiltration
  • a better digital terrain model that incorporated the Environment Agency’s high-quality LIDAR data.

In 2013, an updated Flood Map for Surface Water (uFMfSW) was produced.  The new surface water flood map for England and Wales shows the worst-case flood extents, depths, velocities and hazard ratings for the 30, 100 and 1,000-year return period storm events of one, three and six-hour durations.

The EA maps were not intended to be used for insurance purposes to assess the risk to a particular property but were intended to provide an indication of whether your area may be affected by surface water flooding and to what extent.

Lessons learned for the future?

Recent flooding events have revealed the UK’s vulnerability to extreme rainfall events.  Peter Stott, Head of the Met Office’s climate monitoring and attribution team, believes there is strong evidence that extreme rainfall events are increasing and are likely to become more frequent in future years.

The general scientific consensus is, however, that the summer 2007 floods were not a “climate change event” but rather were a consequence of a combination of unusual (but normal) events such as prolonged heavy rainfall and saturated soil which made it unable to absorb the additional rainfall.

One thing that is clear is that this problem is not going away anytime soon. The NFRR (National Flood Resilience Review) concluded in September 2016 that it was plausible that rainfall experienced over the next ten years could be between 20% and 30% higher than normal.

Insurers are ensuring they are better equipped to deal with the impact of extreme weather events by using data models that are based on up-to-date information and that take account of changing risk patterns to better predict, assess and monitor risk. However, this is not just an insurance issue; it involves government, house builders, local authorities and insurers all working together to ensure the UK becomes more resilient to flooding. With a changing climate and potentially more frequent and more severe flood events in the future, we need to make sure that we take action considering what could happen – failure to adapt is not an option.

Current research indicates that if we are not able to control the average rise in global temperatures then we will subsequently see a significant increase in the risk of flooding. For example, failure to constrain average global temperature rises to within 4 degrees will see the overall risk of UK flooding increase by 150%. It’s a problem that won’t go away and one that needs to be addressed now, not after the next cluster of events.