Aral Sea

Credit: Jesse Allen, Earth Observatory, Posted on: Wednesday, 1 October 2008, 07:27 CDT Download full size image

A Soviet-era plan to turn the arid plains of Kazakhstan, Uzbekistan, and Turkmenistan into fertile cropland resulted in the near-total diversion of the water that once fed the Aral Sea. Prior to the scheme, two rivers—the Amudar’ya in the south and the Syrdar’ya in the north—flowed out of distant mountains and pooled in a desert basin in what is now southern Kazakhstan and northern Uzbekistan. The irrigation project began in the mid-1900s, and by 1960, the sea had already begun to dry out.

This natural-color satellite image shows the Aral Sea on August 16, 2008. The colored contour lines show the approximate shorelines of the sea since 2000. The image is from the MODIS on NASA’s Aqua satellite. The contour lines are based on MODIS data from both the Aqua and Terra satellites. The image documents the progress of a conservation plan to stabilize the North Aral Sea, and the continued decline of the South Aral Sea. Deeper, clearer waters are darker blue; shallower, murkier waters are greenish.

A dam separates the northern and southern parts of the sea, allowing the flow of the Syrdar’y to recharge the North Aral Sea. Meanwhile, the South Aral Sea continues to dry out. The lake has split into eastern and western lobes, with the eastern lobe drying more rapidly. The lakebed is lined with pale, salty sediment, which is kicked up during dust storms. The lakebed sediments also contain agricultural chemical residues and other pollutants, which have contributed to widespread public health problems.

The transformation of the lake into dry land changed the regional climate. Previously, the large lake helped to stabilize the area’s continental climate. Continental climates exhibit large seasonal extremes in temperature. Compared to locations at the same latitude, places with continental climates have hotter summers and colder winters; they are also drier. As the Aral Sea has disappeared, summers have become even hotter, winters have become colder and longer, and the dry climate has become drier.

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