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การหดตัวของทะเลอารัล

ประวัติ

ภาพถ่ายทะเลอารัลทางอากาศ เดือนสิงหาคม 1985

ภาพถ่ายทะเลอารัลทางอากาศ เดือนตุลาคม 2008

ในปี 1918 รัฐบาลโซเวียตมีโครงการเปลี่ยนเส้นทางของแม่น้ำสองสายซึ่งหล่อเลี้ยงทะเลอารัล ได้แก่แม่น้ำอามุ ดาเรีย ทางตอนใต้ และแม่น้ำเซียร์ ดาเรีย ทางตะวันออกเฉียงเหนือ เพื่อสร้างการชลประทานให้พื้นที่ทะเลทรายในการปลูกข้าว เมลอน ธัญพืช และฝ้าย ซึ่งเป็นส่วนหนึ่งของแผนการของโซเวียตเพื่อส่งเสริมให้ฝ้าย หรือทองคำสีขาว กลายเป็นสินค้าส่งออกหลัก โครงการนี้ทำให้ประเทศอุซเบกิสถานกลายเป็นผู้ส่งออกฝ้ายที่ใหญ่ที่สุดประเทศหนึ่งของโลก

การก่อสร้างคลองชลประทานเริ่มขึ้นในช่วงทศวรรษที่ 1940 แต่คลองหลายสายถูกสร้างไม่ดี ทำให้สูญเสียน้ำจากการรั่วและระเหย มีการสูญเสียน้ำประมาณร้อยละ 30 ถึง 75 จากคลองคาราคัมซึ่งเป็นคลองที่ใหญ่ที่สุดในเอเชียกลาง ก่อนถึงปี 1960 น้ำประมาณ 20 ถึง 60 ลูกบาศก์กิโลเมตรไหลไปยังพื้นดินแทนที่จะไหลลงทะเล น้ำที่ไหลลงสู่ทะเลส่วนใหญ่ถูกเปลี่ยนเส้นทาง จนทำให้ทะเลอารัลเริ่มหดตัวในช่วงทศวรรษที่ 1960 ระหว่างปี 1961 ถึง 1970 ระดับน้ำทะเลลดลงเฉลี่ยปีละ 20 เซนติเมตร ในทศวรรษที่ 1970 ระดับเฉลี่ยเพิ่มขึ้นเป็น 50 ถึง 60 เซนติเมตรต่อปี และในทศวรรษที่ 1980 น้ำในทะเลยิ่งลดลงเร็วขึ้น ที่อัตราเฉลี่ย 80 ถึง 90 เซนติเมตรต่อปี การใช้น้ำเพื่อการชลประทานก็เพิ่มขึ้นต่อเนื่องเช่นกัน ปริมาณน้ำที่ถูกนำไปใช้จากแม่น้ำเพิ่มขึ้นเป็นสองเท่าระหว่างปี 1960 และ 2000 ในขณะที่ปริมาณการผลิตฝ้ายก็เพิ่มขึ้นเกือบสองเท่าในช่วงเวลาเดียวกัน อุตสาหกรรมประมงในทะเลอารัลต้องสูญหายไป ทั้งที่ในยุครุ่งเรืองเคยมีการจ้างงานกว่า 40,000 คน และจับปลาได้ถึงหนึ่งในหกของปลาทั้งหมดของสหภาพโซเวียต เช่นเดียวกับการจับหนูมัสแครตบริเวณปากแม่น้ำอามุ ดาเรียและเซียร์ ดาเรีย ซึ่งเคยผลิตขนได้ถึง 500,000 ตัวต่อปี

การหดตัวของทะเลอารัลไม่ได้อยู่นอกเหนือความคาดหมายของโซเวียต ในปี 1964 อเล็กซานดร์ อซาริน แห่งสถาบันไฮโดรโปรเจกต์ ชี้ให้เห็นว่าทะเลสาบนี้ต้องถูกทำลายลงโดยอธิบายว่า "มันเป็นส่วนหนึ่งของแผนห้าปีซึ่งอนุมัติโดยรัฐบาลแห่งสหภาพโซเวียต และโปลิตบูโร ไม่มีใครในตำแหน่งต่ำกว่ากล้าขัดแย้งแผนเหล่านี้แม้แต่คำเดียว ถึงแม้ว่ามันจะเกี่ยวข้องกับชะตาของทะเลอารัลก็ตาม"

The reaction to the predictions varied. Some Soviet experts apparently considered the Aral to be "nature's error", and a Soviet engineer said in 1968 that "it is obvious to everyone that the evaporation of the Aral Sea is inevitable." On the other hand, starting in the 1960s, a large scale project was proposed to redirect part of the flow of the rivers of the Ob basin to Central Asia over a gigantic canal system. Refilling of the Aral Sea was considered as one of the project's main goals. However, due to its staggering costs and the negative public opinion in Russia proper, the federal authorities abandoned the project by 1986.

Current situation

Vozrozhdeniya Island seen
by SPOT satelliteแม่แบบ:Clarify me

Comparison of the North Aral Sea before (below) and after (above) the construction of Dike Kokaral completed in 2005

Abandoned ship near Aral, Kazakhstan

Abandoned ship near Aral, Kazakhstan

A former harbor in the city of Aral, Kazakhstan

From 1960 to 1998, the sea's surface area shrank by approximately 60%, and its volume by 80%. In 1960, the Aral Sea was the world's fourth-largest lake, with an area of approximately 68,000 km² and a volume of 1100 km³; by 1998, it had dropped to 28,687 km², and eighth-largest. The amount of water it has lost is the equivalent of completely draining Lakes Erie and Ontario. Over the same time period its salinity has increased from about 10 g/L to about 45 g/L. As of 2004, the Aral Sea's surface area was only 17,160 km², 25% of its original size. By 2007 the sea's area had shrunk to 10% of its original size, and the salinity of the remains of the southern part of the sea (the Large Aral) had increased to levels in excess of 100 g/L. By comparison, the salinity of ordinary seawater is typically around 35 g/L; the Dead Sea's salinity varies between 300 and 350 g/L.

Even the recently-discovered inflow of water discharge from underground into the Aral Sea will not in itself be able to stop the desiccation. This inflow of about 4 cubic kilometers per year is larger than previously estimated. This groundwater originates in the Pamirs and Tian Shan mountains and seeks its way through geological layers to a fracture zone at the bottom of the Aral Sea.

In 1987, the continuing shrinkage split the lake into two separate bodies of water, the North Aral Sea (the Lesser Sea, or Small Aral Sea) and the South Aral Sea (the Greater Sea, or Large Aral Sea); an artificial channel was dug to connect them, but that connection was gone by 1999 as the two seas continued to shrink. In 2003, the South Aral further divided into eastern and western basins; the loss of the North Aral has since been partially reversed (see below). Shrinkage of the lake also created the Aralkum, a desert on the former lakebed.

Work is being done to restore in part the North Aral Sea. Irrigation works on the Syr Darya have been repaired and improved to increase its water flow, and in October 2003, the Kazakh government announced a plan to build Dike Kokaral, a concrete dam separating the two halves of the Aral Sea. Work on this dam was completed in August 2005; since then the water level of the North Aral has risen, and its salinity has decreased. As of 2006, some recovery of sea level has been recorded, sooner than expected. "The dam has caused the small Aral's sea level to rise swiftly to 38 m (125 ft), from a low of less than 30 m (98 ft), with 42 m (138 ft) considered the level of viability." Economically significant stocks of fish have returned, and observers who had written off the North Aral Sea as an environmental disaster were surprised by unexpected reports that in 2006 its returning waters were already partly reviving the fishing industry and producing catches for export as far as Ukraine. The restoration reportedly gave rise to long absent rain clouds and possible microclimate changes, bringing tentative hope to an agricultural sector swallowed by a regional dustbowl, and some expansion of the shrunken sea. "The sea, which had receded almost 100 km south of the port-city of Aral, is now a mere 25 km away." There are plans to build a new canal to reconnect Aralsk with the sea. Construction is scheduled to begin in 2009, by which time it is hoped the distance to be covered will be only 6 km. A new dam is to be built based on a World Bank loan to Kazakhstan, with the start of construction also slated for 2009 to further expand the shrunken Northern Aral eventually to the withered former port of Aralsk.

The South Aral Sea, which lies in poorer Uzbekistan, was largely abandoned to its fate. Projects in the North Aral at first seemed to bring glimmers of hope to the South as well: "In addition to restoring water levels in the Northern Sea, a sluice in the dike is periodically opened, allowing excess water to flow into the largely dried-up Southern Aral Sea." Discussions had been held on recreating a channel between the somewhat improved North and the desiccated South, along with uncertain wetland restoration plans throughout the region, but political will is lacking. Uzbekistan shows no interest in abandoning the Amu Darya river as an abundant source of cotton irrigation, and instead is moving toward oil exploration in the drying South Aral seabed. Vast salt plains exposed with the shrinking of the Aral have produced dust storms, making regional winters colder and summers hotter. Attempts to mitigate these effects include planting vegetation in the newly exposed seabed. In the Northern Aral, recently higher sea levels have slightly moderated these effects in some areas, and the spring season now sees long-missing rainfall.

As of summer 2003, the South Aral Sea was vanishing faster than predicted. In the deepest parts of the sea, the bottom waters are saltier than the top, and not mixing. Thus, only the top of the sea is heated in the summer, and it evaporates faster than would otherwise be expected. Based on the recent data, the eastern part of the South Aral Sea is expected to be gone within 15 years; the western part could last for another 50-125 years.

The ecosystem of the Aral Sea and the river deltas feeding into it has been nearly destroyed, not least because of the much higher salinity. The receding sea has left huge plains covered with salt and toxic chemicals, which are picked up and carried away by the wind as toxic dust and spread to the surrounding area. The land around the Aral Sea is heavily polluted and the people living in the area are suffering from a lack of fresh water and health problems, including high rates of certain forms of cancer and lung diseases. Crops in the region are destroyed by salt being deposited onto the land. The town of Moynaq in Uzbekistan had a thriving harbor and fishing industry that employed approximately 60,000 people; now the town lies miles from the shore. Fishing boats lie scattered on the dry land that was once covered by water; many have been there for 20 years. The only significant fishing company left in the area has its fish shipped from the Baltic Sea, thousands of kilometres away.

Possible solutions

Many different solutions to the different problems have been suggested over the years, ranging in feasibility and cost, including the following:

• Improving the quality of irrigation canals;
• Installing desalination plants;
• Charging farmers to use the water from the rivers;
• Using alternative cotton species that require less water;
• Using fewer chemicals on the cotton;
• Moving farming away from cotton;
• Installing dams to fill the Aral Sea;
• Redirecting water from the Volga, Ob and Irtysh rivers. This would restore the Aral Sea to its former size in 20–30 years at a cost of US$30–50 billion;
• Pump and dilute sea water into the Aral Sea from the Caspian Sea via pipeline.

In January 1994, the countries of Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan and Kyrgyzstan signed a deal to pledge 1% of their budgets to helping the sea recover.

In March 2000 UNESCO presented their Water-related vision for the Aral Sea basin for the year 2025 at the 2nd World Water Forum in The Hague. This document was criticized for setting unrealistic goals, and also for giving insufficient attention to the interests of the area immediately around the former lakesite, implicitly giving up on the Aral Sea and the people living on the Uzbek side of the lake.[1]

By 2006, the World Bank's restoration projects especially in the North Aral were giving rise to some unexpected, tentative relief in what had been an extremely pessimistic picture.