Long‐term hydrological changes of the Aral Sea observed by satellites

The Aral Sea has been shrinking since the former Soviet Union constructed irrigation projects to divert water from its main rivers in the 1960s. The diminishing of the Aral Sea is “one of the worst environmental disasters in the world” (from United Nations Secretary-General Ban Ki-moon). In this study, 33 years of satellite observations from Advanced Very High Resolution Radiometer (AVHRR) and 21 years of satellite altimetry sea level data from TOPEX/Poseidon, Jason-1, and Jason-2 are used to quantify the long-term hydrological changes in the Aral Sea. A simple algorithm with AVHRR channels 1 and 2 albedo is developed to identify and discriminate the water pixels from land and cloud. Thus, monthly water coverage in the region can be reliably generated. The water coverage maps since 1981 show constant decline of the Aral Sea. The coverage dropped from ∼4.7–4.8 × 104 km2 in 1981 to about ¼ of this value in the recent years. In fact, drastic hydrological change was observed in the main Aral Sea during the 2000s. In the South Aral Sea, sea level shows a steady decrease from 35 m above sea level to <26 m since 1993. Total loss of water storage since 1993 is estimated to be ∼2.0 × 102 km3 for the South Aral Sea with a rate of ∼16−20 km3/yr before 2002, and a smaller value after 2002. In 1990, the North Aral Sea was observed to separate from the main Aral Sea. Water coverage, sea level, and total water storage were kept relatively stable for the period between 1993 and 2013 in the North Aral Sea. A water level increase and coverage expansion occurred during the 2005−2006 period when a dam was built in 2005 between the North Aral Sea and the South-East Aral Sea.

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