Groundwater discharge into the Aral Sea after 1960

The dramatic shrinkage of the Aral Sea that has occurred after 1960 has affected also groundwater resources in the region, and this effect needs to be clarified and quantified because groundwater is essential for meeting freshwater demands in the area. We determine upper and lower limits for the groundwater discharge into the Aral Sea after 1960, by use of water balance expressions, treating the groundwater as a fitting parameter and considering the uncertainty of the dominant evaporation term in the Aral Sea water balance equation. We also independently analyze, from a pure groundwater hydraulic perspective, the relative effects of the on-going sea surface lowering since 1960 on the hydraulic gradient and thereby also the groundwater discharge into different regions of the Aral Sea. These independent analyses yield consistent results in terms of the total groundwater discharge into the Aral Sea being equal or greater than in 1960, with some relevant scenario results yielding increased groundwater discharge up to about 200% of the 1960 value. In terms of regional groundwater discharge distribution, the present (2002) discharge into the southeast part of Large Aral is not greater than it was 1960; analyses of about 3000 different and relevant parameter combinations show that this prediction is robust with respect to uncertainty in parameter values. The groundwater discharge into the northwest part of Large Aral and into the Small Aral, however, should have increased due to the on-going sea level lowering. Furthermore, for an unchanged absolute groundwater discharge, its relative importance for the Aral Sea(s) has increased dramatically, from being about 12% of the total river discharge in 1960 to about 100% of total river discharge presently, and constitutes now a critical factor for the fate of the present lake system.