London, October 8 (ANI): Giant ribbons of moist air flowing north from the tropics, each of which carry 1,000 times more water than the Thames, are behind the recent floods and wet summers in Britain, scientists believe.
The 'atmospheric rivers', which bring the equivalent of the Amazon's content in rain, are thought to have caused the worst 10 winter floods to have hit the UK since 1970.
Now scientists believe that they may also be linked to heavy rain in the summer, suggesting they pose an all-year threat to the country's flood defences.
Measuring up to 300 miles wide and extending up to 2,000 miles from the tropics to northern Europe, these rivers can bring torrential rainfall that lasts days.
According to researchers, there are only four or five parts of the world where the ribbons form and one of them is located above Britain.
The UK is particularly vulnerable because of its mountainous west coast, which causes the moisture-laden air to rise and cool, creating rain clouds.
A study by meterologists at Reading University found that atmospheric rivers caused winter floods, including those which devastated Cumbria in November 2009 and Cornwall in November 2010.
But the phenomenon has also been linked to the heavy downpours that hit Britain in June, and scientists believe the ribbons may be to blame for flooding which struck large parts of the country in the summer of 2007.
For years, the cause of Britain's wet summers has been identified as the jet stream, a fast-flowing band of air more than 30,000ft up which brings Atlantic depressions over the country when it moves south.
While the jet stream is almost certainly a factor, scientists now believe the atmospheric rivers also contribute to the heavy rainfall.
The Reading University team looked into the subject at the request of the Natural Environment Research Council, which has set aside 15 million pounds to pay for studies into Britain's changing weather patterns.
Led by atmospheric scientist David Lavers, the team's work involved flying research aircraft into storms and using satellites to follow the movement of masses of moist air.
The scientists found that much of the rain falling in Britain comes from water evaporated from the warm Atlantic waters west of Portugal and north Africa.
Between eight and 10 times a year, Atlantic depressions generate a narrow band of wind which carries the water to Britain.
Having found the atmospheric rivers, which had been invisible to most scientific instruments, researchers are expected to look into how they could be affected by climate change.
There are fears that rising temperatures will lead to more flooding as warm air can carry more moisture.
"Damage from flooding in the winter and fall seasons has been widespread in the United Kingdom (UK) and Western Europe over recent decades," the Daily Mail quoted the study's abstract as reading.
"Here we show that winter flood events in the UK are connected to Atmospheric Rivers (ARs), narrow ribbons along which a large flux of moisture is transported from the subtropics to the mid-latitudes.
"Combining river flow records with rainfall measurements, satellite data and model simulations, we demonstrate that ARs occur simultaneously with the 10 largest winter flood events since 1970 in a range of British river basins, suggesting that ARs are persistently critical in explaining extreme winter flooding in the UK.
"Understanding the physical processes that determine the persistence of AR events will be of importance in assessing the risk of future flooding over north-western Europe and other mid-latitude regions," it added. (ANI)