Growing threat of surface water flooding

  • An increase in extreme weather events across UK is causing a host of different problems
  • 3.8 million properties in England alone are susceptible to pluvial flooding
  • Zurich can act quickly if a property owner is affected

Seen by many as an invisible hazard, pluvial – or surface water – flooding can often strike with little warning in areas not usually prone to flooding.

And increases in extreme weather events across the UK, quite possibly brought about by climate change, are exacerbating the risks for properties thought to be in danger from pluvial flooding – namely low-lying urban areas.

Greater numbers at risk

Commonly, flooding occurs when water levels rise and rivers burst their banks – also known as fluvial flooding – or when high tides and stormy weather cause coastal flooding. But less well known are the risks associated with pluvial events, which are caused by intense periods of rainfall.

In 2013, the Environment Agency estimated that around 3 million properties in England are susceptible to surface water flooding, compared to 2.6 million properties that are at risk of fluvial or coastal flooding.

Difficult to predict

“The Environment Agency has developed an early warning system alerting when river levels are high, but no such warnings exists for surface water,” said Paul Redington from Zurich’s Property Major Loss team.

Accurately predicting pluvial flood risks has been notoriously difficult as there are no easily defined flood plains like there are for rivers and seas. Buildings, street furniture and how well the sewers and associated infrastructure all react to a sudden deluge can all also significantly affect the final outcome of a pluvial flood event.

“Places most at risk are where you have run-off from surrounding areas into a central low-lying land – a prime example of this would be the city of Hull,” said Colin Prince, Deputy Underwriter Manager for Real Estate at Zurich.

In the summer of 2007 following a period of persistent wet weather, Hull was one of the many towns and cities across England to be affected after bursts of heavy rainfall triggered multiple flooding events and saw insured flood losses total £3bn across the country.

Our changing infrastructure

And this danger is only likely to get worse due to a combination of climate change as well as an expected increase in the UK’s urban population, planning regulations that encourage building in flood risk areas and as-yet limited investment by water and sewerage companies to update Victorian-era systems, notably in London.

“This problem is also exacerbated by less green spaces,” said Paul. “Urban development, concreting over driveways and the deregulation of planning for many home extensions means that water has nowhere to go. For instance, Thames Water has said that impermeable surfaces in London have doubled in the last five years.

“And new residential developments with multiple occupation are putting pressure on already overburdened and ageing sewer and drainage infrastructure.”

Managing your risk

At the end of 2013, Environment Agency flood maps were finally updated to include details of pluvial flooding, in a bid to provide a more detailed assessment of overall flood risk.

However, as Colin explains, this still has its limitations: “The problem with mapping out the threat is that it is very difficult to identify which areas are susceptible unless there has been a history within that particular area,” said Colin.

“Quite often the claims we see for this type of loss come up as a low flood risk as it is very difficult to predict.”

Having a mixture of flood resistance to stop the water entering in the first place and flood resilience to minimise the damage once it is in will mitigate the damage as far as possible

Paul Redington, Zurich’s Property Major Loss team

The risks can be mitigated, especially when it comes to building new properties or refurbishing old ones. Having adequate drainage and run-off areas – especially in urban locations where run-off space is generally at a premium – and being both resilient and resistant to flooding are vital.

“Obviously, having a mixture of flood resistance to stop the water entering in the first place and flood resilience to minimise the damage once it is in will mitigate the damage as far as possible,” said Paul.

“And practical things like separating storm and foul water systems. In a claim situation, contaminated water makes clean up more difficult and expensive, and can mean tenants being out for much longer.

“Developers, too, should identify opportunities for landscaping – green spaces, but also what’s known as ‘blue’ spaces – set aside for storing water, or conveying pluvial storm water to drains.”

Find out more and access helpful guides and insight with our new Flood Risk Resource.