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.