The recent evolution of the Aral Sea level and water properties: analysis of satellite, gauge and hydrometeorological data

The recent drop of sea level in the Aral Sea of about 0.6 m year−1 during the last 40 years represents one of the most dramatic example globally about the possible consequences of man-induced environmental changes. This extremely strong signal, as well as the constantly changing hydrological and meteorological fluxes in this area are missing from the seaborne observations in the 1990s because the observational network developed by the Former Soviet Union has almost not been operating during one decade in the new independent states. Fortunately, the Aral Sea level has been regularly monitored from space, in particular by satellite altimetry. In this study, we present observations of the Aral Sea level and analyze the observed trends and shorter term variability based on TOPEX/Poseidon altimeter data. This data set (available since early 1993) is complemented by hydrometeorological data and gauge data (since 1950) allowing to quantify the evolving water balance of the Aral Sea. It is shown that even though the river runoff almost ceased recently, the rapid drawing of the Aral Sea is substantially reduced by the compensating discharge of ground water. The analysis of the available data makes it possible to address the changing salt balance and to identify the major control on this balance exerted by ground water discharge. The major event of ground water discharge is identified in the period 1993–1994 and resulted in a substantial increase of the salt content. The rapid drop of salt content thereafter could indicate an increase of salt precipitation.