History and Analysis of Water Loss in the Aral Sea
By Justin Abel, Daniel O'Crowley, and Logan Sleezer
ES 771: Remote Sensing
Once the world’s fourth largest lake, the Aral Sea supported thriving fishing and fur harvesting industries. Over 40,000 metric tons of fish were harvested in 1960, providing 40,000 jobs and accounting for 1/6 of the Soviet Union’s fish catch (Howard, 2014). Beginning in the 1960’s, the rivers that once fed the Aral Sea were diverted in order to grow melons, rice, wheat, and most importantly cotton. Twenty-thousand miles of canals and more than 80 reservoirs were constructed to irrigate the arid region (Wines, 2002). Since implementation of the diversion program, the lake has dwindled to 10% of its original size (Micklin and Aladin, 2008).
The Aral Sea is encompassed by the Kara-Kum and Kyzyl-Kum deserts. Prior to diversion, the Syr Darya and Amu Darya flowed into the brackish, endorheic (closed-basin) lake. Though the lake basin lies on the border of Kazakhstan and Uzebekistan, the catchment area includes the following countries: Afghanistan, Iran, Kyrgyzstan, Tajikstan, and Turkmenistan. Both rivers are fed primarily by snow and glacier melt from the mountains of Afghanistan, Tajikstan, and Kyrgyzstan. The Aral Sea basin’s (region) desert lowland climate is characterized by cold winters and hot summers. Annual average rainfall in the region ranges from less than 100 millimeters (mm) per year to around 200 mm per year. Potential evapotranspiration (PET) ranges from 1000 mm to over 2250 mm. During modern times and prior to diversion, the balance between inflow from the rivers and loss due to surface evaporation had remained relatively stable. Between 1911 (when measurements began) and 1960 the lake’s water level held around 53 meters (m) above sea level (asl), with annual fluctuations of around 1 m (Micklin, et al., 2014).
Consequences of Diversion:
As a result of the diversion program, 10 million acres of land were converted to agriculture (Wines, 2002). During the Soviet era, Uzbekistan produced nearly 2/3 of the world’s cotton (Rumer, 1989). Though the diversion program was successful at bringing widespread agriculture to the desert, it had many negative environmental impacts on the region.
Much of the diverted water was lost before it could be used for irrigation. Eighteen percent of the water diverted from the Amu Darya was lost, 75-99% of which was attributed to infiltration from unlined canals (Saiko, 2001). Salinity in the lake rose from 10 grams per liter (g/l) to over 100 g/l. As a result, biodiversity of the lake was drastically reduced. The fish population was decimated and the number of fish species dropped from 32 to 6. By the mid 1980’s the fishing industry was essentially gone.
Abandoned fishing vessel stranded on the dry basin of the Aral Sea (Wikimedia Commons, 2003).
As the water receded, sediments containing toxic agricultural chemicals deposited over decades were exposed. Dust storms now carry salt and chemical laden sediments as far as 500 kilometers. Breathing and ingestion of the dust has resulted in high levels of respiratory illness, throat and esophageal cancer, and digestive disorders in the local population. Liver and kidney ailments, as well as eye problems are also common. The loss of fish from the local diet has resulted in increased malnutrition and anemia. Deposition of the salt-laden dust retards the growth of crops and natural vegetation (Micklin and Aladin, 2008).
Massive dust storm, originating from the Aral Sea, blows west across the Kakhstan-Uzbekistan northwestern border (NASA, 2008).
To track changes in water level in the Aral Sea, satellite imagery was acquired covering the Aral Sea and the surrounding area from the United States Geological Survey (USGS) Global Visualization Viewer website (http://glovis.usgs.gov/). Specifically, multiband imagery from the Landsat series of satellites was obtained for the years of 1987, 2001, and 2016 (Landsat 5, Landsat 7, and Landsat 8 respectively). Significant effort was made to select multiband image sets with minimal cloud-cover and from the same approximate time of year (August-September) to limit influence of seasonal variation. 144 images were used for analysis including data from 6 bands (1, 2, 3, 4, 5, and 7) from 8 different aerial viewpoints encompassing the Aral Sea for each of the 3 years.
Image sets for each year were first imported into ArcMap 10.4 software to stitch together images from the 8 aerial viewpoints using the 'Mosaic' tool. Mosaics were made for each of the 6 bands for each year excluding zero values to eliminate black collars from each of the images used in the mosaics. Once all mosaics were complete, each one was exported as a .tiff image file. Each of these images was then imported into Idrisi Selva software using the 'Tiff to Idrisi' conversion tool. The 'composite' tool in Idrisi was then used to create false-color composite images for each year using the mosaic images representing band 1, band 5, and band 7 (assigned as blue, green, and red respectively). Cluster analysis, using all 6 mosaicked band images per year, was also performed within Idrisi to isolate water areas. Cluster images for each of the 3 years were then reclassified to contain only two classes representing 'water' and 'other'. The reclassified clusters were used to approximate water area for each year in Idrisi as a means of comparison between years. Finally, Microsoft Excel software was used to graph water surface area over time and the best fit line of this data was used to infer average Aral Sea loss in water surface area per year from 1987 to 2016.
Time Series showing change in water surface area from Landsat imagery (left column) and derived cluster analysis in Idrisi (right column).
Graphical representation of derived surface water area measurements from cluster analysis.
Results and Discussion:
The analyses indicate an average Aral Sea surface water loss of approximately 1150 square kilometers per year from 1987 to 2016, resulting in an overall surface water loss of 33263 square kilometers. Unfortunately, cluster analysis classified cloud-covered areas as water in most cases and this error in analysis may have led a slight overestimation in water area for each year. Shi et al. (2014) used data from the Advanced Very High Resolution Radiometer (AVHRR) in a similar study to derive average yearly Aral Sea water surface area loss from 1981 to 2014 as approximately 1000 to 1200 square kilometers per year. The similarity of the surface water area loss we reported with the estimation of Shi et al. (2014) gives confidence that cloud cover did not greatly affect our results and that our results are an accurate representation of Aral Sea water surface area loss from 1987 to 2016.
Future of the Aral Sea:
Today the lake is separated into the Northern Aral Sea and the Southern Aral Sea. The Southern Aral Sea can be further divided into the eastern and western lobes. Returning the Aral Sea to its original extent is unlikely due to the region's dependence on irrigated agriculture. In fact, most of the countries in the region actually intend to increase irrigation in order to support growing populations.
In 2005, Kazakhstan completed construction of Dike Kokaral. The dam was constructed to block outflow from the Northern Aral Sea. As a result, the Northern Aral Sea has risen, salinity has dropped, and the fisheries have improved. As the salinity continues to settle many more indigenous fish species are expected to return (Micklin and Abedin, 2008).
Rehabilitation of the Southern Aral Sea will be much more difficult. Plans have been proposed to increase inflow from the Amu Darya by reducing water losses to leaky canals and planting less water-intensive crops. However, implementation of this plan would be quite costly and could have a negative economic impact on the region (Micklin and Abedin, 2008).
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