Present-Day Water Balance of the Aral Sea Seen from Satellite

The Aral Sea shrank drastically over the past 50 years, largely due to water withdrawal from Amu Darya and Syr Darya rivers for land irrigation. This has led to the separation of Aral Sea into two (in 1986–1987) and then four (in approximately 2010) water bodies. Lakes and enclosed inland seas are integrators of environmental and climate changes occurring at regional to global scale and present a high variety of behaviors on a variety of time scales (from seasonal to decadal) depending on many factors, natural and anthropogenic. In addition, their crucial importance as water stocks has increased the necessity of monitoring all of their morphodynamics characteristics, such as water level, surface (water contour) and volume. The satellite altimetry and satellite high resolution optical imagery together are now widely used for the calculation of lakes and reservoirs water storage changes worldwide. Based on these different techniques we can determine the water extent within the Aral Sea basin since 1993, as well as volume variations, which is key parameter in the understanding of hydrological regime at time scales ranging from months to decades in this largely ungauged basin. Remote sensing techniques coupled with complementary in situ data have allowed precisely quantifying the water balance of the Aral Sea since 1993 and to understand the recent desiccation of this inland sea. Moreover, unprecedented information can be obtained by coupling models and surface observations with data from space, which offers global geographical coverage, good spatial-temporal sampling, continuous monitoring over time, and the capability of estimating water mass change.