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Tuesday, July 15

Amazing GRACE and California's groundwater: Water Crisis Gordian Knot, Part 7

A stunning technological achievement but with very bad news to report.  Yet GRACE could give humanity the edge it needs, on the theory that there would have been no chance without governments here and around the world, from the federal to municipal levels, knowing exactly where they stand in terms of their groundwater supplies. 

See the National Geographic website for the many links in the article below, including link to the NASA GRACE Mission website. 

A note regarding the author's mention in passing of Nevada's vast Lake Mead: On July 10 the Associated Press reported that the water level in the lake had dropped to an all-time low; the lake is now at 39 percent of its capacity.  (Its 'sister' reservoir farther up the Colorado River, Lake Powell, is at 52 percent capacity.)  Officials had projected the decline at Lake Mead and don't expect there will be cuts to water deliveries to Nevada and Arizona this year or next, but they give a 50-50 chance there will be cuts in 2016 (depending on drought conditions).  Las Vegas, a city of 2 million residents, is almost completely dependent on Lake Mead for its drinking water.
Epic California Drought and Groundwater: Where Do We Go From Here?

Posted by Jay Famiglietti of University of California, Irvine
in Water Currents via National Geographic Society
February 4, 2014

Yesterday our team at the UC Center for Hydrologic Modeling released a report on the California drought.  The report describes the bird's eye view of statewide water resources that we see from the NASA GRACE satellite mission.

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 the major aquifers in the 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 freshwater, 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 freshwater 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.

A second contribution of the report is that it further exposes the unsustainable pattern of groundwater use in the Central Valley.  While there is some replenishment of groundwater during wet years, groundwater levels decline precipitously during drought, when farmers have no choice but to rely far more heavily on groundwater to meet their irrigation water needs.
[...]
All right. There's much more to the report, and again, numerous links to papers, satellite data, the GRACE mission, etc., but I think the above is enough to convey the picture.  More than 80 percent of California's water use goes to agriculture, and much of that is in the two valleys that make up the Central Valley -- San Joaquin and Sacramento.  Triage efforts will have to focus there first, but this running smack dab into the state's hydropolitics, which is almost cosmic in complexity.  .
              
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