NASA Finds New Way to Monitor Underground Water Loss
hubie writes:
The Central Valley of California makes up only 1% of U.S. farmland, but produces 40% of the nation's produce despite only receiving 5 to 10 inches (12 to 25 centimeters) of rainfall a year. That kind of productivity is due to massive pumping of groundwater for irrigation. After decades of pumping, parts of California are literally sinking and water is getting harder to get at (wells in the Tulare Basin have to be drilled a kilometer deep).
Groundwater in this region comes from two sources that are separated by a dense layer of clay. The water on top of the clay resides in loose soil and this water gets replenished with rainfall and snowmelt runoff. The water below the clay is the aquifer and this is not replenished. A major problem is that nobody knows where the pumped water is being pulled from, nor how much of it remains.
A research team from NASA's Jet Propulsion Laboratory and the U.S. Department of Energy's Lawrence Berkeley Laboratory came up with a new method to monitor changes between the two water sources.
They attacked the problem by combining data on water loss from U.S.-European Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On satellites with data on ground-level changes from a[sic] ESA (European Space Agency) Sentinel-1 satellite. Ground-level changes in this region are often related to water loss because when ground is drained of water, it eventually slumps together and sinks into the spaces where water used to be - a process called subsidence.
[...] The researchers created a simple numerical model of these two layers of soils in the Tulare Basin. By removing the long-term subsidence trend from the ground-level-change data, they produced a dataset of only the month-to-month variations. Their model revealed that on this time scale, virtually all of the ground-level change can be explained by changes in aquifers, not in the water table.
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