Impacts of Changes in Natural Factors and Human Activities on Surface Water Variations in the Aral Sea Basin

Abstract

Surface water in the Aral Sea Basin has undergone rapid changes since the 1960s, leading to severe environmental issues that have attracted global attention. This study quantified surface water variations in the Aral Sea Basin from 1986 to 2021 based on all available Landsat images integrated in the Google Earth Engine platform, and further analysed the impacts of changes in natural factors and human activities on surface water variations in the upstream, midstream, and downstream of the basin. The results indicate that the total surface water area in the basin decreased significantly from 56 058.79 km² to 26 292.35 km² during 1986–2021, showing a net loss of 29 766.44 km² at a rate of 845.36 km²/a. The surface water area in the upstream and midstream exhibited modest increases at the rates of 69.92 km²/a and 39.80 km²/a respectively, while that in the downstream suffered a drastic reduction at a rate of 955.08 km²/a. The Aral Sea experienced the most drastic shrinkage in space, shrinking from 68 478 km² in 1960 to 9397.31 km² in 2021 at a decreasing rate of 999.17 km²/a, accompanied by water level and volume decline rates of 0.37 m/a and 17.18 km³/a, respectively. Natural factors, particularly glacier melting induced by climate warming, primarily drive surface water variations in the upstream mountains. In contrast, human activities, especially damming and irrigation, dominate surface water variations in the mid-downstream areas. Although the increased reservoir storage has slightly boosted surface water in the midstream, the strong diversion of runoff has caused severe surface water depletion in the downstream, constituting the predominant driver of surface water deficits across the entire basin.