When it comes to water scarcity, the loss of groundwater is like the silent killer: It isn't as easy to measure or monitor as, say, a shrinking reservoir. We've known that many aquifers are overtaxed, but a new report shows we're draining major aquifers faster than they're being replenished. Not just in California — this is happening everywhere.
A new study from the University of California, Irvine, looked at 37 major aquifers in the world using data from NASA and other indicators. Each aquifer was assigned a Total Groundwater Stress (TGS) ratio measuring total storage as compared to depletion rate to assign timelines. One third of the aquifers — which provide food and water to two billion people — are being depleted at accelerated rates. At least eight of those are categorised as "overstressed," meaning they are losing water at the fastest rate.
One part of the study estimated that the Northwest Sahara Aquifer System — a massive groundwater source which covers most of northern Africa — could be depleted up to 90 per cent of its total storage in 50 years.
In many cases, agricultural practices are to blame, as aquifers are being drained to feed growing populations; about 20 per cent of all food is grown with groundwater. Now compound that with the lack of precipitation in many areas which doesn't percolate back into the aquifer fast enough to replace the water that's is being extracted. Industries like oil production have also been blamed as they pull out groundwater as part of extraction process. And it's not just the fact that there's less water to use. Losing groundwater is bad for other reasons: It kills trees, makes the ground sink, and can eventually cause the aquifer itself to collapse.
I've reported before on NASA's Gravity Recovery and Climate Experiment (GRACE) satellite, which is able to measure groundwater by looking at regional gravitational attraction. But as the study mentions, this data is not precise — scientists still need to compare it with on-the-ground well data. The problem in a place like California, for example, is that farmers aren't yet required to report on how much groundwater they're taking out of the aquifer every year. And after a series of dry years, they might not know how bad it is until it's too late.