Long-term, non-anthropogenic groundwater storage changes simulated by three global-scale hydrological models

Area of Science:

• Hydrology
• Climate Science
• Environmental Science

Background:

• Groundwater storage is a critical component of the global water cycle.
• Quantifying natural groundwater variability is essential for distinguishing anthropogenic impacts.

Purpose of the Study:

• To investigate the long-term, natural variability of global groundwater storage.
• To understand the influence of climate patterns on groundwater dynamics.
• To establish a baseline for assessing human-induced changes in groundwater.

Main Methods:

• Utilized three global-scale hydrological models forced with over 50 years of meteorological data.
• Validated model outputs using in situ groundwater observations and satellite-derived terrestrial water storage (GRACE).
• Employed empirical orthogonal function analysis to identify climate influences, such as ENSO.

Main Results:

• Models demonstrated reasonable representation of inter-annual water storage variability (correlation > 0.5).
• The El Niño Southern Oscillation (ENSO) significantly influences global groundwater storage.
• Global natural groundwater storage exhibited a decreasing trend over the last 5-7 decades, with rates varying from 0.01 to 2.18 mm/year.

Conclusions:

• Natural, non-anthropogenic variability in groundwater storage is substantial.
• Low-frequency (inter-decadal) variability complicates trend identification.
• Accurate assessment of human impacts on groundwater requires a thorough understanding of its natural variability.