Saturday, November 10, 2012

Receding Aral Sea sees some recovery



This image, taken on August 26, 2010, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, demonstrates the close connection between the Aral Sea and the Amu Darya River. It is the most recent image in a ten-year sequence published on the Earth Observatory’s World of Change: Shrinking Aral Sea. Photo Credit: NASA/Jesse Allen


The size of the Aral Sea has long hinged on the Amu Darya, which flows from the high Pamir Mountains in central Asia, across the desert, and into the southern sea. While two rivers empty into the lake—the Amu Darya and the Syr Darya—the Amu Darya is the largest and most fickle source of water. At times in ancient history, the river has bent its course to empty into the Caspian Sea, and the abandoned Aral Sea shrank. The Aral Sea has been at its largest when the Amu Darya feeds it.

Modern trends are no exception: when water began to be diverted from the Amu Darya for vast agricultural projects starting in 1960, the Aral Sea began to shrink.

Between 2000 and 2009, the Aral Sea steadily shrank. In 2006, severe drought settled in over Amu Darya Basin. Very little water reached the Aral Sea in 2007, and nothing flowed from the Amu Darya to the Aral Sea in 2008 and 2009. Without water from the Amu Darya, the southern Aral Sea rapidly dwindled, the eastern lobe all but disappearing in 2009.

In 2010, however, the drought broke. Snow in the Pamir Mountains was normal, and enough water flowed into the Amu Darya that the river reached the Aral Sea. The muddy pulse of water settled in a shallow layer over the bed of the eastern lobe of the South Aral Sea, making it look much larger than it had in 2009.

Before 1960, the Aral Sea was the fourth largest lake in the world. However, much of the Amu Darya and Syr Darya have been diverted for agriculture, limiting the flow of water into the sea. Since 1960, the Aral Sea has lost 88 percent of its surface area and 92 percent of its water volume.

Water withdrawal and availability in Aral Sea basin

Millions of years ago, the northwestern part of Uzbekistan and western Kazakhstan were covered by a massive inland sea. When the waters receded, they left a remnant sea known as the Aral.

The Aral as an inland salt-water sea has no outlet being fed by the Amu Darya and Syr Darya Rivers. The fresh water from these two rivers once held the Aral’s water and salt levels in balance. However after the 50ies and 60ies when a series of major irrigation schemes were undertaken on the two rivers by Soviet Engineers the water started to recede.

The schemes were based on constructing a series of dams on both two rivers to create reservoirs from which eventially 40.000 km of canals would be dug to divert water to field crops. Afterwards however there was little or no water left in the riverbeds to flow to the Aral Sea. Consequently the water level in the last 50 years in the Aral has dropped by approximately 23 metres and the volume has been reduced by nearly 90%.

Whilst triggering what is considered one of the 20th Centuries greatest ecological disasters; these schemes are however unlikly to be removed as they are the main source of income and food for millions of people in the region.

 
Photo: Around the remaining sea is a vast salt plain now known as the Aralkum Desert, a result of the sea's evaporation. The desert is a roughly 15,444-square-mile (40,000-square-kilometer) zone of dry, white salt and mineral terrain. Each year sandstorms pick up at least 150,000 tons of salt and sand from Aralkum and transport them across hundreds of miles, causing severe health problems for the local population and altering the region's climate.

Reference: Micklin, P. (2010, September 16). The past, present, and future Aral Sea. Lakes & Reservoirs: Research & Management, 15 (3), 193-213. Sources: http://thewatchers.adorraeli.com/2011/07/26/receding-aral-sea-sees-some-recovery/ http://earthobservatory.nasa.gov/IOTD/view.php?id=46685

ED: Sadly this was short lived read National Geographic article from October 2014 - "Aral Sea's Eastern Basin Is Dry for First Time in 600 Years" go to http://news.nationalgeographic.com.au/news/2014/10/141001-aral-sea-shrinking-drought-water-environment/