NASA’s GRACE satellites have produced a spectacular database that can be used to look beneath the Earth’s surface. Launched in 2002, these satellites measure Earth’s gravity field at high precision, allowing small changes in where mass is distributed in the Earth’s crust to be discovered.
|NASA's GRACE Satellite|
One of the big ways this happens is through groundwater pumping. When groundwater is pumped to the surface and used, it either evaporates or runs off towards the ocean, removing mass from an area. GRACE therefore gives scientists the ability to monitor how groundwater has been used over the last decade.
A key area for groundwater usage is in the Western U.S. That area has, on average, had its driest 10 years out of the last century, leading to huge drawdowns in water in Lake Mead and Lake Powell, the reservoirs on the Colorado River.
But that isn’t the only water source being used up. Using data from GRACE, scientists led by Dr. Stephanie Castle at UC Irvine were able to calculate how much water has been extracted from the ground in the area over the past 10 years.
Their result is staggering. Since 2004, the groundwater depletion in the Colorado River basin is the equivalent of twice the volume of Lake Mead.
Let’s say that again. Groundwater is a finite resource and in the past decade alone, areas like Arizona, Colorado, California, New Mexico, and Nevada have pumped out and used 2 Lake Meads worth of water from the ground.
This dataset doesn’t tell how much water is there in the ground to be used, but that volume is staggering. There has been a lot of focus, from us included, on the management of water levels in Lake Mead and its potential impacts on the area. To think that groundwater pumping in the region is using up two of those every 10 years means the region is relying far more on a finite resource than almost anyone would have guessed. At those usage rates, if groundwater supplies began to dry up, replacing that water would use up the entire Lake Mead reservoir in 5 years.
Image credit: US Department of Agriculture