So THAT'S why we've been getting so much rain! Scientists find 'atmospheric rivers' in the sky which hit Britain with 1,000 times more water than the Thames
- Giant ribbons of moist air flowing north from the tropics bring heavy rain
- Some 'rivers' carry as much water as the Amazon
- Ribbons blamed for worst 10 winter floods to hit Britain since 1970
- Researchers say they are also linked to the country's recent wet summers
Giant ribbons of moist air flowing north from the tropics - each carrying 1,000 times more water than the Thames - are to blame for Britain's recent floods and wet summers, 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 they may also be linked to heavy rain in the summer, suggesting they pose an all-year threat to the country's flood defences.
Why does it always rain on us? This graphic shows how huge 'atmospheric rivers' in the sky are causing floods in Britain. Water from warm Atlantic waters west of Portugal and north Africa evaporates and the moist air is carried north by depressions. The air cools as it rises above Britain's mountainous west coast, producing heavy cloud and then downpours
Deluge: An aerial view of Tewkesbury, Gloucestershire, in the summer of 2007. Scientists believe giant ribbons of moist air flowing from the Atlantic are causing flooding in Britain all year round
Submerged: Scientists believe the 2007 flooding in Tewkesbury may have been caused by ribbons of moist air each carrying 1,000 times more water than the River Thames
Measuring up to 300 miles wide and
extending up to 2,000 miles from the tropics to northern Europe, they
can bring torrential rainfall that lasts days.
Researchers say there are only four or five parts of the world where the ribbons form - and one of them is located above Britain.
UK is particularly vulnerable because of its mountainous west coast,
which causes the moisture-laden air to rise and cool, creating rain
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.
Recurring problem: Tewkesbury was hit by flooding again in May this year. Scientists believe the heavy rainfall was caused by moist air flowing north from the tropics
Water, water everywhere: Researchers have found that atmospheric rivers are to blame for the worst 10 floods to hit Britain since 1970, including those which affected Cockermouth in Cumbria in November 2009
Inundated: The River Derwent burst its banks and flooded properties in Cockermouth, Cumbria, in 2009
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 £15million 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.
Dangerous: A car struggles to make its way through water in St Blazey, Cornwall, in November 2010, one of the 10 worst winter floods to hit Britain since 1970
Help: A girl gets a piggyback during floods in the village of Lostwithiel, near St Austell, Cornwall, in 2010
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.
Downpours: A Lostwithiel resident's home is protected by sandbags in November 2010 (left) and floodwater surrounds local shops (right) in the centre of Mytholmroyd near Huddersfield, West Yorkshire, in June 2012
The study's abstract reads: 'Damage from flooding in the winter and fall seasons has been widespread in the United Kingdom (UK) and Western Europe over recent decades.
'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.'
No entry: Floodwater swells the River Ouse as it flows through York in September this year, almost covering road signs
Giant: The strongest ribbons of moist air carry more water than the Amazon, the world's longest river, scientists believe
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