Over the past 50 years, the Aral Sea has lost 90 per cent of its water – mostly due to removal for irrigation for cotton growing. Using data from NASA’s GRACE satellites, Kirk Zmijewski and Richard Becker mapped monthly changes in mass within the lake’s 1.5-million-square- kilometre catchment between 2003 and 2012. These changes are directly related to changes in water volume, both on and below the land surface.
The results, obtained by a new study by scientists from the University of Toledo in Ohio, and published in Earth Interactions, indicated that over the study period, the catchment area lost an average of 12–14 cubic kilometres per year. However, this was only about half the rate at which the Aral Sea itself lost water during that period. ‘That means that roughly half the water lost from the Aral Sea has entirely left the watershed, by evaporation or agricultural uses, but half is upstream within the watershed,’ said Becker.
A closer examination of the data indicated that the central part of the catchment, where almost all of the region’s farming takes place, actually increased in mass during the last four years of the study. The researchers suggest that this increase was due to a combination of improvements in water conservation and water seeping out of unlined ditches into aquifers.
This story was published in the April 2014 edition of Geographical Magazine