Yesterday the team at the UC Center for Hydrologic Modeling released a report on the California drought. The report describes the birds-eye view of statewide water resources that we see from the NASA GRACE satellite mission.
We’ve been working since the mid-1990’s, well before the mission was launched in 2002, to develop and test methods to help monitor groundwater depletion from space. We’ve applied them around the world — in California, across the U. S., in the Middle East, East Africa, in the Amazon River basin and in India.
Our endgame is simple. We want to use GRACE and other satellites, combined with invaluable measurements on the ground, to help quantify how regional and global freshwater availability is changing.
The good news is that the methods work great. The GRACE mission functions like a giant ‘scale in the sky,’ weighing how various regions around the world are gaining and losing water each month. We can see the ups and downs of ‘total’ water storage – all of the snow, surface water, soil moisture and groundwater – like never before.
The bad news is that we are running out of groundwater.
In particular, this is happening in the places that we need it most — the dry parts of the planet where we love to live, precisely because it does not rain. Out of necessity, our reliance on groundwater in these parts of the world is much greater than elsewhere.
Our team and several others around the globe are showing that most of major aquifers in world’s arid and semi-arid regions are being depleted at a rapid pace, and one that is most likely unsustainable in the long term. Groundwater is a finite resource after all.
What has GRACE shown us about California?
Our earlier study showed that between October, 2003 and March, 2010, the Sacramento and San Joaquin River basins lost about 30 cubic kilometers of fresh water, nearly the equivalent of the full volume of Lake Mead. Of this, we determined that about two-thirds was due to groundwater depletion in the Central Valley.
During the drought of 2006-2010, state and federal surface water allocations were drastically reduced, forcing farmers to tap groundwater reserves far more heavily than in ‘normal,’ wetter years. The resulting volume of depleted groundwater was so great that it was registered by a satellite ‘scale’ that orbits about 400 km above Earth’s surface.
Our new report is an update to this previous work, and it points to one critical question for California.
One of the key numbers to emerge from the report is that the combined Sacramento and San Joaquin River basins have already lost 10 cubic kilometers of fresh water each year in 2012 and 2013.
To put that number in perspective, it is roughly the amount of water used by the entire population of California, for household, municipal and industrial use (that is, for nearly everything else besides agriculture and environment). It is also the steepest decline in total water availability that our team has witnessed in the 12 years that we have been monitoring California water resources with the GRACE mission. More
