A scientific analysis of the severe floods in central England last July has found that they were exceptional events that cannot be linked to climate change.
The scale of last year's flooding had prompted experts to suggest they were due to climate change and a harbinger of similar summer-time flooding to come.
However, in a report published today by the Centre for Ecology and Hydrology in Wallingford, researchers analysed flooding trends across England for the last four decades and found there appears to be a trend for less summer flooding, but more rainfall in winter. Last July's floods were highly unusual, the researchers said.
"The rainfall ... was remarkable," said Terry Marsh, of the centre. "[It] fuelled speculation that flood risk is increasing due to global warming. Due to the inherent variability of the UK climate, any extreme hydrological event cannot readily be linked directly to climate change."
The researchers said a historical perspective showed how extraordinary last summer's floods were. They hit Gloucestershire, Oxfordshire, and towns along the rivers Severn and Avon particularly hard.
Between May and July last year, average rainfall for England and Wales was 415mm - by far the highest ever recorded in data that goes back to 1766. In a league table of the 15 wettest years only one other (1924) occurred in the 20th century. In the three summer months in 1924, 308 mm of rainfall fell - 107 mm less than the equivalent months last summer, the equivalent of seven weeks of average rainfall.
The detailed data on river flows for the last four decades reinforces the theory that last year's flooding was exceptional. In an analysis in the International Journal of Climatology, Marsh, and his colleague Jamie Hannaford, show that river flows have increased, but these increases are mostly confined to the north and west. "This trend is driven by an increase in, generally, winter high flows," said Hannaford. So the 2007 summer floods occurred in the wrong season and the wrong place to be part of that trend. "The summer 2007 floods don't really fit into these patterns."
The increase in winter flooding would fit with predictions from some climate modellers for wetter winters and drier summers. However, Hannaford said it was impossible to say definitively that the apparent trends in the data are down to global warming. The British climate is simply too variable from year to year to be sure. "We have only 40 years of data which generally is too short to determine whether or not these trends are caused by any underlying climatic mechanism."
Even if climate change increases rainfall, it might lower the risk of flooding at some times of year, for example, by leading to less snow melt in spring and higher temperatures which dry soils earlier.
Marsh said climate change could even provide "a silver lining" in that drier summers could limit the winter flood period because the soil would absorb more water.
In "Guardian"
http://www.guardian.co.uk/environment/2008/mar/11/flooding.scienceofclimatechange
The scale of last year's flooding had prompted experts to suggest they were due to climate change and a harbinger of similar summer-time flooding to come.
However, in a report published today by the Centre for Ecology and Hydrology in Wallingford, researchers analysed flooding trends across England for the last four decades and found there appears to be a trend for less summer flooding, but more rainfall in winter. Last July's floods were highly unusual, the researchers said.
"The rainfall ... was remarkable," said Terry Marsh, of the centre. "[It] fuelled speculation that flood risk is increasing due to global warming. Due to the inherent variability of the UK climate, any extreme hydrological event cannot readily be linked directly to climate change."
The researchers said a historical perspective showed how extraordinary last summer's floods were. They hit Gloucestershire, Oxfordshire, and towns along the rivers Severn and Avon particularly hard.
Between May and July last year, average rainfall for England and Wales was 415mm - by far the highest ever recorded in data that goes back to 1766. In a league table of the 15 wettest years only one other (1924) occurred in the 20th century. In the three summer months in 1924, 308 mm of rainfall fell - 107 mm less than the equivalent months last summer, the equivalent of seven weeks of average rainfall.
The detailed data on river flows for the last four decades reinforces the theory that last year's flooding was exceptional. In an analysis in the International Journal of Climatology, Marsh, and his colleague Jamie Hannaford, show that river flows have increased, but these increases are mostly confined to the north and west. "This trend is driven by an increase in, generally, winter high flows," said Hannaford. So the 2007 summer floods occurred in the wrong season and the wrong place to be part of that trend. "The summer 2007 floods don't really fit into these patterns."
The increase in winter flooding would fit with predictions from some climate modellers for wetter winters and drier summers. However, Hannaford said it was impossible to say definitively that the apparent trends in the data are down to global warming. The British climate is simply too variable from year to year to be sure. "We have only 40 years of data which generally is too short to determine whether or not these trends are caused by any underlying climatic mechanism."
Even if climate change increases rainfall, it might lower the risk of flooding at some times of year, for example, by leading to less snow melt in spring and higher temperatures which dry soils earlier.
Marsh said climate change could even provide "a silver lining" in that drier summers could limit the winter flood period because the soil would absorb more water.
In "Guardian"
http://www.guardian.co.uk/environment/2008/mar/11/flooding.scienceofclimatechange