Global reservoir storage variations in the 21st century

Reservoirs are critically important for water management under increasing water demands and a changing climate. However, information about reservoir storage variations is very limited at the global scale. To fill in this data gap, a global monthly storage dataset was generated using multi-source satellite observations for 7245 reservoirs (6653 km³ total storage capacity) from 1999 to 2018. It was found that global total reservoir storage has increased at a rate of 27.44 ± 0.96 km³/yr, with 75% of the growth found in Asia (20.53 ± 0.73 km³/yr). Such changes are primarily attributed to the many newly constructed reservoirs, which have impounded significantly more water In contrast, a significant decrease of the normalized storage—the ratio of the actual storage over the storage capacity—suggests that global reservoirs are experiencing water shortages. Although the global runoff values are much higher during the last three years (2016-2018) than before, the corresponding normalized storage values only increased moderately —which indicates that global reservoirs are suffering from increasing water stress. In particular, Asian reservoirs are more sensitive to runoff, and they experience low normalized storage values but large intra-annual variations. This suggests that they are under greater pressure.