Weighing the water: how a pair of satellites tracks the Earth's changing gravity field
Background
Terrestrial water storage is the total water held on and under the land, including surface water, soil moisture, groundwater, snow and ice.
The Gravity Recovery and Climate Experiment, known as GRACE, and its successor GRACE Follow-On measure it indirectly, by detecting changes in the Earth's gravity field as water moves.
Because water has mass, a region that gains or loses water changes the pull it exerts on a passing satellite.
The record built from these missions runs from April 2002 to November 2025.
A study published in the Proceedings of the National Academy of Sciences used that record to separate human-driven changes from climate-driven ones.
It found that in four continental regions a human-related variable explained the trend better than any climate variable, and that retreating Himalayan glaciers accounted for 15 per cent of the decline in northern India.
In plain words
Terrestrial water storage Terrestrial water storage — All water held on and under the land surface, from soil moisture to groundwater, snow and ice.
Gravimetry Satellite gravimetry — Measuring mass changes on the Earth from the gravity they exert on a spacecraft.