On the Desiccation of the South Aral Sea Observed from Spaceborne Missions

Abstract

The South Aral Sea has been massively affected by the implementation of a mega-irrigation project in the region, but ground-based observations have monitored the Sea poorly. This study is a comprehensive analysis of the mass balance of the South Aral Sea and its basin, using multiple instruments from ground and space. We estimate lake volume, evaporation from the lake, and the Amu Darya streamflow into the lake using strengths offered by various remote-sensing data. We also diagnose the attribution behind the shrinking of the lake and its possible future fate. Terrestrial water storage (TWS) variations observed by the Gravity Recovery and Climate Experiment (GRACE) mission from the Aral Sea region can approximate water level of the East Aral Sea with good accuracy (1.8% normalized root mean square error (RMSE), and 0.9 correlation) against altimetry observations. Evaporation from the lake is back-calculated by integrating altimetry-based lake volume, in situ streamflow, and Global Precipitation Climatology Project (GPCP) precipitation. Different evapotranspiration (ET) products (Global Land Data Assimilation System (GLDAS), the Water Gap Hydrological Model (WGHM)), and Moderate-Resolution Imaging Spectroradiometer (MODIS) Global Evapotranspiration Project (MOD16) significantly underestimate the evaporation from the lake. However, another MODIS based Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) ET estimate shows remarkably high consistency (0.76 correlation) with our estimate (based on the water-budget equation). Further, streamflow is approximated by integrating lake volume variation, PT-JPL ET, and GPCP datasets. In another approach, the deseasonalized GRACE signal from the Amu Darya basin was also found to approximate streamflow and predict extreme flow into the lake by one or two months. They can be used for water resource management in the Amu Darya delta. The spatiotemporal pattern in the Amu Darya basin shows that terrestrial water storage (TWS) in the central region (predominantly in the primary irrigation belt other than delta) has increased. This increase can be attributed to enhanced infiltration, as ET and vegetation index (i.e., normalized difference vegetation index (NDVI)) from the area has decreased. The additional infiltration might be an indication of worsening of the canal structures and leakage in the area. The study shows how altimetry, optical images, gravimetric and other ancillary observations can collectively help to study the desiccating Aral Sea and its basin. A similar method can be used to explore other desiccating lakes.

Water Balance Analysis Based on a Quantitative Evapotranspiration Inversion in the Nukus Irrigation Area, Lower Amu River Basin

“…Several studies have examined the water balance elements in the irrigation areas of the Aral Sea Basin but have mostly focused on single elements such as evapotranspiration (ET) or runoff. For example, Singh et al [13] used Gravity Recovery and Climate Experiment (GRACE) and MODIS Global Evapotranspiration Project (MOD16) data with a coarse resolution to analyze changes in water mass and ET in the lower Amu Darya River irrigation area. Nezlin et al [11] and Asarin et al [4] analyzed runoff from the Amu Darya River into the Aral Sea over decades.…”

METRIC and WaPOR Estimates of Evapotranspiration over the Lake Urmia Basin: Comparative Analysis and Composite Assessment

“…This heightens the need for more accurate measurements of regional water and energy cycle components for planning, prediction, and mitigation of negative social and environmental aspect of such changes. ET has remained one of the mostly poor measured component of water and energy cycle in most regions of the world, a good example of which is Lake Urmia and Aral Sea [35]. It is hoped that the new generation of instruments (e.g., ECOSTRESS [36], among others) can provide more reliable estimate of ET regionally and globally.…”

Historical Change and Ecological Risk of Potentially Toxic Elements in the Lake Sediments from North Aral Sea, Central Asia

“…Research examining the environmental evolution of lake sediments in the Aral Sea has mainly been focused on the systematic study of changes in the historic climate, vegetation, and other environmental components over long-term scales since the Quaternary [16][17][18][19]. In view of research findings, more remote sensing techniques were used to assess the impact of human activities on the Aral Sea and its watersheds, to explore the causes of lake shrinkage and to predict the lake's future destiny [20][21][22]. The current environmental status of water, soil and sediment within the Aral Sea basin was determined [23].…”