Identifying drivers of storage dynamics of lakes and reservoirs in the arid Central Asia

Abstract Knowing the storage variations in lakes and reservoirs are essential for water resources and environmental management, especially in the regions facing water scarcity. However, the quantification of the storage changes is limited by sparse in-situ observations and spatial coverage of space (air)-borne altimetric sensors that have been used conventionally in storage retrieval. This hampers the attribution analysis of lake storage changes. Here, we combined long-term optical remote sensing and multi-source terrain elevation data to derive the monthly storage time series from 1990 to 2020 for 8544 lakes and reservoirs in Central Asia, where water scarcity has been bottle-necking local socioeconomic sustainability. The regional total storage has been decreasing with a rate of −4.78 ± 0.88 km 3 yr −1 mainly owing to the desiccation of the Aral Sea. For other lakes, 26% of them show decreasing while 22% show increasing trends. At a watershed-scale, the long-term changes in small to medium-sized (<5000 km 2 ) lakes are primarily caused by the changes in surface runoff, jointly affected by precipitation and temperature changes. We also found that 29% lakes in Central Asia experienced frequent seasonal dry out in the past decades. Such seasonal dry out is mainly caused by fast evaporation losses during the summer months. For the majority (63 ± 8%) of these lakes, their evaporation water losses are larger than the seasonal storage drawdown. Our analysis highlights the co-regulation of surface runoff and lake evaporation in the storage losses in arid and semi-arid regions.