How measuring tiny shifts in gravity reveals our planet's disappearing water
In short: We cannot see groundwater from the surface, but we can feel its weight from orbit. By tracking subtle fluctuations in Earth's gravitational pull, a specialized pair of satellites is mapping the invisible movement of ice, snow, and vital underground reservoirs across the globe.
Since its launch in 2002, NASA’s Gravity Recovery and Climate Experiment (GRACE) has provided a unique window into the Earth's water cycle. The mission operates by observing changes in the planet's gravity field. Because water has mass, any significant movement or depletion of water—such as melting glaciers or receding aquifers—alters the local gravitational pull. By monitoring these minute gravitational shifts, scientists can estimate how much water is being stored or lost in specific regions.
This technique is particularly vital for monitoring resources that are otherwise impossible to track globally. For example, the mission has documented the depletion of ice and snow mass in the Himalayas and the draining of groundwater reservoirs in Australia. In California, the data reveals a staggering trend in the Central Valley aquifer. Over a ten-year period, the loss in this region was estimated to be approximately 1.5 times the total capacity of Lake Mead, with roughly 30 cubic kilometers of that loss attributed specifically to groundwater.
To maintain this critical longitudinal study, the mission transitioned to the GRACE Follow-On (GRACE-FO) mission, which launched in May 2018. This continuation allows water managers and scientists to analyze long-term trends in resource consumption. By combining gravity data with estimates of surface soil moisture and snow levels, researchers can calculate precise changes in groundwater volume, providing essential intelligence for managing the world's most precious, yet hidden, liquid assets.
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Sources
- Summary by Intellect · source: Science Bulletins: GRACE—Tracking Water from Space
- Also: GRACE: Tracking water from space
- Also: Tracking Groundwater Changes Around the World Using Satellite Gravity | NASA Earthdata
- Also: Tracking Water from Space – GRACE-FO
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