2007 floods ‘no link to climate’
By Richard Black
Environment correspondent, BBC News website
Water overwhelmed drainage systems in several regions of Britain
The UK’s summer floods of 2007 were a freak event unrelated to global climate change, according to a report from the Centre for Ecology and Hydrology (CEH).
The key cause was that extended rains early in summer soaked soils that would normally have been dry at that time.
When heavy storms came later, water could not soak away into the ground.
The report said data does not support the notion that UK summer rainfall is increasing or rivers are showing faster flow rates than in previous years.
That said, 2007 did break a number of records. In particular, rainfall in June and July was about 20% higher than ever seen before in records that go back to 1879.
Climate change predictions mean we can expect to see more extreme weather events such as flooding in the future
“The river floods of summer 2007 were a very singular episode, which does not form part of any clear historical trend or show consistency with currently favoured climate change scenarios,” said the report’s lead author, Terry Marsh.
The flooding affected areas of Britain from Humberside and Yorkshire to Gloucestershire and the south-west of England.
It claimed 14 lives, forced 55,000 families and 6,000 businesses to move away, and caused damage worth at least £3bn.
Some of the statistics that CEH’s researchers have compiled make powerful reading.
In Pershore, Worcestershire, the storm on 19 and 20 July saw more than 10mm of rain per hour for six consecutive hours.
A rain gauge in Hull recorded 44% of its average annual rainfall in just two weeks.
Tributaries of the Severn, Humber and Thames flowed faster than they have ever done since meters were put in place.
Soggy summer in stats
But many areas might have escaped the consequences of such spectacular downpours if soils had not been already saturated.
This meant that extraordinary volumes of water ran off the soil into rivers. Run-off into the Avon near Evesham was 80% greater than the maximum previously seen since records began 70 years ago.
But, against long-term series of data, 2007 appears to be a blip rather than part of a trend.
Summers do not appear to be getting wetter – in fact there was more summer rain around during the 19th Century than there is today.
Records for maximum flows on the Avon and Thames, which both date back into the 1800s, show no long-term increase.
What has changed since then, the researchers conclude, is the growth of urban centres, particularly on floodplains.
“Extreme flooding in the UK is historically rare; but vulnerability to flooding has increased markedly as a consequence of floodplain development,” said Mr Marsh.
“This is despite increased resilience to flood risk through improved flood alleviation strategies, and more sophisticated flood warning capabilities.”
The lack of adequate warnings and the importance of moving building programmes away from floodplains in the future were highlighted in the government-commissioned independent review of the floods, enacted by Sir Michael Pitt.
Less is more?
The agency itself believes that climate change is likely to bring regular echoes of 2007.
The floods inundated about 55,000 homes across the country
“Although we cannot attribute last summer’s floods to climate change, climate change predictions mean we can expect to see more extreme weather events such as flooding in the future,” a spokeswoman for the agency told BBC News.
“This year, government announced an increase in funding for flood risk management which will help us develop our flood risk and warning systems.
“We also need to make sure homes – particularly for those who are vulnerable – are built in a safe place, and that people and the environment are protected.”
But the CEH report suggests the opposite may be true; flooding may become less severe as climate change progresses.
The basis for this assessment lies in UK Met Office projections that, while heavy summer rains may become more frequent, summers are likely to be drier overall, especially in the south of Britain.
As the CEH report notes, warmer, drier summers should result in ground able to absorb more water when storms come.
Higher temperatures are also likely to reduce snowmelt in spring, which can cause sharp floods.