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Last Updated: Wednesday, 30 July, 2003, 11:47 GMT 12:47 UK
Satellite shows dramatic Aral loss
By Ivan Noble
BBC News Online science staff

These two images from space show how unsustainable water use in Central Asia has caused a dramatic retreat in the Aral Sea.

Fishing town Muynak is now 150 km from water, Esa
The fishing town Muynak is now 150 km from water
In the 18 years which separate the images, the sea has virtually split in two and a great white expanse of salty desert has claimed the seabed revealed by the contracting waters.

The most recent image was taken this month by the European Space Agency's Medium Resolution Imaging Spectrometer (Meris) on board Envisat, the world's most powerful environmental monitoring satellite.

The older image is from 1985 and was taken by the US space agency Nasa's space shuttle crew.

Thirsty cotton

The Aral Sea lies on the border between the former Soviet republics of Uzbekistan and Kazakhstan, but the waters which feed it rise thousands of kilometres away in the Pamir Mountains.

The European Space Agency's Envisat imaged the sea in July 2003

The great Amu Darya and Syr Darya rivers were known in history as the Oxus and Jaxartes. They flow through much of Central Asia before they reach the Aral.

Along the way much of their water is taken for the irrigation of thirsty cotton crops.

Large scale irrigation began in the 1960s and has led to the Aral losing half its area and three-quarters of its volume.

Former fishing villages are now dozens of kilometres away from the shoreline.

A Nasa space shuttle took this image of the Aral Sea in 1985

Sands laden with salt and pesticide residues are whipped up into storms by a climate no longer subject to the sea's moderating influence.

The independent states of Central Asia are now joined in an association to manage the waters that feed the Aral but in practice there is little agreement among them on how best to share the resource.

The cotton irrigation systems are old and leaky, so much of the water is wasted.

Watching the seas

The Meris instrument's primary mission aboard Envisat is to monitor sea colour.

"It essentially sees the world the way we see it, though it can also see into the infrared," explained Peter North, lecturer in geography at the University of Swansea, UK, and member of the Meris validation team.

"What it's good at is spotting changes over time," he told BBC News Online.

Meris can observe how plankton spread through the Earth's oceans, providing a valuable insight into the way the seas act as a counterweight to global warming by storing carbon dioxide.

Meris' field of view means that it can provide an almost daily view of any given point on Earth.

Its host satellite, Envisat, was launched on an Ariane 5 in 2002. The satellite is the biggest and most expensive Earth-observation spacecraft ever built by Europe.

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