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Friday, 17 March, 2000, 01:02 GMT
Winters really are getting wetter
rainbow and traffic
The pattern: Wetter winters and drier summers
By environment correspondent Alex Kirby

British winters are turning wetter, according to UK climate scientists - because we are getting more days of downpours which dump huge quantities of rain in a short time.

We're now living in a semi-artificial climate system. There is very likely a human influence behind this trend

Dr Mike Hulme
The scientists, from the University of East Anglia and the Hadley Centre for Climate Prediction and Research, have published their findings in the International Journal of Climatology.

Their work, which was supported by the UK Government's Department of the Environment, Transport and the Regions, shows that the heaviest daily rainfalls now contribute about twice as much to total winter rainfall as they did in the early 1960s.

Decades of change

In summer months, they say, an opposite trend has been identified, with days of heavy rain making a decreasing contribution to total rainfall.

The research results are based on more than 100 weather stations with records stretching back to 1961, supported by longer records from a smaller number of stations.

people with umbrellas
Rain . . . and the forecast is for more
One of the scientists involved, Dr Tim Osborn, said: "If you are interested in heavy rainfall, it is the total rain that falls in a day or a few days that is important, and you have to start analysing daily weather records.

"We used daily rainfall totals and found that important changes have occurred over the last few decades in the occurrence of the heaviest rainfalls."

The authors say the trends in rainfall intensity "show some agreement with climate model predictions of human-induced climate change, though natural climate variability cannot be ruled out at this stage".

Climatologists have known for some time that total winter rainfall in the UK is increasing, and researchers in the US and Australia have made similar findings there.

Increasing confidence

Another of the scientists involved in the UK research, Dr Mike Hulme, told BBC News Online: "What we're now finding is that there are more days with the heaviest amounts of rain.

flooded street with boat
More flooding is likely
"The interesting point of this research is that it provides us with one further piece of evidence in the global jigsaw that points towards climate change being caused in part by human pollution.

"Bit by bit, it's building up our confidence. The findings do point to a trend which seems not to be related to natural climate variability.

"There's a natural phenomenon, the North Atlantic Oscillation (NAO), which controls a lot of our winter weather. But this rainfall increase doesn't work in parallel with the NAO.

"The NAO is not the primary cause of the increase. There's something else going on.

"We're now living in a semi-artificial climate system, not an entirely natural one. There is very likely a human influence behind this trend."

Going to waste

Dr Merylyn MacKenzie-Hedger, of the UK Climate Impacts Programme, part of the Environmental Change Institute at the University of Oxford, said the winter rainfall increases had several implications in other areas as well.

"Heavy rainfall events can cause rapid run-off and place extreme pressure on drainage systems. Blockages can rapidly cause local flooding.

"Not all the rain may be captured in water storage systems, and so it may not be available to meet increased water demand during summer droughts."

However, the emphasis on human-induced change by these climatologists will be questioned by other scientists who believe that the influence of pollution has been overstated.

These researchers believe that current computer models are still not powerful enough to simulate accurately the complex processes at work in the atmosphere.

They also question the notion that the Earth is undergoing a period of rapid warming. Although surface data do show an increase in temperatures in the last two decades, these sceptics of global warming point to the data produced by satellite and balloon studies of atmospheric temperatures which show little or no warming.

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See also:

18 Nov 99 | Sci/Tech
Climate change warning
04 Nov 99 | Sci/Tech
Europe's climate forecast is hot
10 Mar 00 | Sci/Tech
Air pollution stops rain
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