Aral Sea

The Aral Sea has been drying up since the 1960s as a result of the large amounts of water diverted by cotton farmers from the two rivers flowing into it, the Syr Darya and the Amu Darya. Indeed, the shoreline has receded by more than 120 kilometers in places and the Aral Sea has since split into two basins, the Large Aral and the Small Aral, each supplied by one of the rivers.

The drastic drop in the Aral Sea level continues. Because of an intensive irrigation in the upstream basins, this lake has lost much of its water volume and area since 1960 (approximately 70 000 km2 in the 1960s and 20000 km2 in the early 2000s).
In 1989, the Aral Sea divided into two basins : the Large Aral Sea and the Small Aral Sea. The Large Aral should soon be itself divided. Already very salty, (80g/l, almost the salinity of the Dead Sea), this basin sees its ecosystem falling and almost disappearing, except for the rare species that can survive in an environment too salty.
If things seem desperate for Large Aral (at least as long as irrigation lasts), the Small Aral is likely to be stabilized, thanks to the reconstruction of the dam, which had failed in 1999 (just after the Image of the Month, July 1999 : Aral Sea could be rising from the dust ?).

Aral Sea remote sensing in 1973 (on the left, image Landsat, Credits Nasa) in 2007 (on the middle, image Modis, Credits Nasa) and in July 2009 (on the right, Credits Esa). 

This is not the first time the Aral Sea is drying up. Already at the beginning of our era, and especially during the Middle Ages (probably as a result of irrigation), the Aral Sea has been drained. The ecological condition and especially health condition are nonetheless worrying in the region, with respiratory diseases caused by sand, salts and pesticides left on the shores of the drained sea, and that the winds carry very far.

Since 1992, the observations began by Topex/Poseidon (and Jason-1 since 2001) allow accurate measurements of the rate of decline in the Aral Sea level. For the Large Aral, the average loss rate is 50 cm per year since 1992. If the water level continues to decline at this rate, the eastern shallow part of the Large Aral will be quickly drained.

Time series of Large Aral Sea level (left) and Small Aral Sea level (right) from altimetric data. The lower accuracy of altimetry measurements on Small Aral Sea is due to the disposal of ground tracks satellites and its geometrical configuration-it is more jagged-. In this context, the footprint of the radar targets heterogeneous surfaces (land and water) and the return signal is noisy. Credits Legos.

For the Small Aral, whose the level is 3 m to 7 m above the Large Aral, the behavior is different. Periods of declining level follow periods of rising level. These fluctuations correspond to the building attempts of a dam between the two seas, in order to retain the waters of the Syr Darya in the northern basin and try to save the Small Aral Sea at the expense of the Large Aral. One of the dam built between the two seas made the Small Aral level rise by 3 m, and its area increased from 4000 to 6000 km2. But in April 1999, the water pressure broke the new dam, causing the significantly low level recorded this year. The authorities in Kazakhstan, with the assistance of international programs, plans to continue this work.

Further information:

  • Altimetry applications in videos: Aral Sea