Evolution of sea level of the big Aral Sea from satellite altimetry and its implications for water balance

The Aral Sea was one of the biggest lakes in the world before it started to shrink in the 1960s due to water withdrawal for land irrigation. Sea level decreases led to the separation of the Aral Sea into two basins-the Small Aral in the north and the Big Aral in the south. For several decades there were no continuous observations of Aral Sea level, and the few data that exist are fragmentary or unavailable. We present observations of the Big Aral Sea level estimated from the TOPEX/Poseidon (TIP) altimetry with high temporal resolution over the last decade (1993-2004). Since sea volume is one of the key parameters for the studies of water balance, we use the TIP-derived time series of sea level and a dedicated digital bathymetry model (DBM) to reconstruct temporal changes in the Aral Sea surface and volume. We introduce variations of the sea volume as the new constraint for the water budget of the Big Aral Sea. This is an important step toward estimating detailed seasonal and interannual changes of the water budget. We assess various existing components of the water budget of the Aral Sea and discuss the quality of the existing data and their applicability for establishing detailed water balance. In particular, large uncertainties in estimating the evaporation and underground water supply are addressed. Desiccation of the Aral Sea resulted in dramatic changes in the salinity regime and, consequently, affected its aquatic ecosystems. We also discuss changes in the aquatic fauna and their possible evolution under continuing desiccation of the Big Aral Sea. Combining satellite altimetry with other parameters of the water budget offers a promising potential for assessing temporal changes in the water budget of and or semi-ard regions, even those with a poor ground monitoring network.