Water Storage Monitoring in the Aral Sea and its Endorheic Basin from Multisatellite Data and a Hydrological Model

Evaporation from the hypersaline Aral Sea in Central Asia

The Aral Sea, once the world's fourth largest lake, has shrunk by 91 % in area and 95 % in volume since 1960s. The shrinkage has resulted in a notable increase in water salinity, which may affect the surface evaporation. Despite previous studies, the hydrological consequences of salinity in the Aral Sea have often been overlooked. In this study, we investigated the impact of water surface salinity on evaporation by employing a water activity-based Penman salinity equation, and we explored its effects on the water balance of the Aral Sea. We established an empirical relationship between the water activity and water salinity. The results indicated that the evaporation rates were overestimated when salinity effects were excluded from evaporation estimations in Aral Sea, especially for the hypersaline South Aral Sea. During the period from 2000 to 2020, the evaporation of a 16 km3 water volume could have been overestimated if the salinity effects were ignored. When calculated from updated evaporation and the lake water balance, the inflow from the middle reaches to the Aral Sea showed significant deviations from the existing data sources. We emphasize that, the observed runoff at stations is higher than our estimated inflow.

Impacts of Human Activities on the Variations in Terrestrial Water Storage of the Aral Sea Basin

Assessing the impacts of human activities on the variations in terrestrial water storage (TWS) is essential for water resource management, particularly in regions like the Aral Sea Basin which suffers from severe water scarcity. In this study, the variations in TWS anomalies (TWSA) of the Aral Sea Basin during the period of April 2002 to June 2017 were analyzed using Gravity Recovery and Climate Experiment (GRACE) data and the Global Land Data Assimilation System (GLDAS) Noah model outputs. The impacts of human activities on TWS variations were further quantified through the variations in TWS components and the comparison of TWS obtained from GRACE and GLDAS. The results indicate that TWSA of the entire Aral Sea Basin derived from GRACE experienced a significant decreasing trend of 4.12 ± 1.79 mm/year (7.07 ± 3.07 km3/year) from 2002 to 2017. Trends in individual TWS components indicate that the reduction in TWS of the Aral Sea Basin was primarily attributed to surface water loss, followed by groundwater depletion, which account for ~53.16% and 11.65 ± 45.39 to 42.48 ± 54.61% of the total loss of TWS, respectively. Precipitation (P) and evapotranspiration (ET) both exhibited increasing trends, indicating that ET played a dominant role in TWS depletion from the perspective of water balance. The variations in ET and TWS induced by human activities contributed ~45.54% and ~75.24% to those in total ET and TWS of the Aral Sea Basin, respectively.