Global freshwater storage and flows are constantly changing with oscillations and persistent trends driven by the combined influence of human activity, climate change, and natural variability on sub-seasonal to multi-decadal timescales.
Human dominance over the water cycle is increasingly apparent and the continued development of global hydrological models enables better representations of human and climate change impacts on water resources. However, the science of understanding the reciprocal impacts of freshwater storage and stress on humans and ecosystems remains in its infancy at the global scale.
Freshwater stress is represented by the state of demand-driven water scarcity and is defined as the ratio of freshwater withdrawal to streamflow. Trends in freshwater storage, however, represent the evolution of total storage, defined as the vertical sum of groundwater, soil moisture, surface water and snow water equivalent storages.
The study found that 201 (42%) of the 478 currently stressed basins are simultaneously losing freshwater storage. These basins are located in south and southwestern USA, northeastern Brazil, central Argentina, Algeria, and are concentrated throughout the Middle East, the Caucasus, northern India, and northern China. Mostly, these regions are agriculturally significant and heavily irrigated. In contrast, 98 (21%) of the currently stressed basins are gaining freshwater storage. Although previous work has shown that the world’s dry regions are becoming drier while the wet regions are becoming wetter, this work reveals that the stressed regions of the world are becoming drier while the non-stressed regions of the world have no clear overall trend in freshwater storage.