Groundwater provides 25 to 40 percent of all drinking water worldwide, and is the primary source of freshwater in many arid countries, according to the National Groundwater Association. About 60 percent of all withdrawn groundwater goes to crop irrigation. In the United States, the number is closer to 70 percent. In much of the world, however, underground reservoirs or aquifers are poorly managed and rapidly depleted due to a lack of water-level data. Developing useful groundwater models, availability predictions and water budgets is very challenging.
...Until now, the only way a water manager could gather data about the state of water tables in a watershed was to drill monitoring wells. The process is time and resource intensive, especially for confined aquifers, which are deep reservoirs separated from the ground surface by multiple layers of impermeable clay. Even with monitoring wells, good data is not guaranteed. Much of the data available from monitoring wells across the American West is old and of varying quality and scientific usefulness. Compounding the problem, not all well data is openly shared.
...The basic concept: Satellites that use electromagnetic waves to monitor changes in the elevation of Earth's surface to within a millimeter could be mined for clues about groundwater. The technology, Interferometric Synthetic Aperture Radar (InSAR), had previously been used primarily to collect data on volcanoes, earthquakes and landslides.
With funding from NASA, the researchers used InSAR to make measurements at 15 locations in Colorado's San Luis Valley, an important agricultural region and flyway for migrating birds. Based on observed changes in Earth's surface, the scientists compiled water-level measurements for confined aquifers at three of the sampling locations that matched the data from nearby monitoring wells....
An irrigation system near Monterey, California, shot by Brendel, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license