Needed: 11 Trillion Gallons to Replenish California Drought   
       
   Dec. 16, 2014: It will take about 11 trillion gallons of water (42 cubic   
   kilometers) -- around 1.5 times the maximum volume of the largest U.S.   
   reservoir -- to recover from California's continuing drought, according to a   
   new analysis of NASA satellite data.   
       
   The finding was part of a sobering update on the state's drought made possible   
   by space and airborne measurements and presented by NASA scientists Dec. 16 at   
   the American Geophysical Union meeting in San Francisco. Such data are giving   
   scientists an unprecedented ability to identify key features of droughts, data   
   that can be used to inform water management decisions.   
       
   A team of scientists led by Jay Famiglietti of NASA's Jet Propulsion   
   Laboratory in Pasadena, California used data from NASA's Gravity Recovery and   
   Climate Experiment (GRACE) satellites to develop the first-ever calculation of   
   this kind -- the volume of water required to end an episode of drought.   
       
   http://www.nasa.gov/mission_pages/Grace/index.html   
       
   NASA satellite data reveal the severity of California's drought on water   
   resources across the state. This map shows the trend in water storage between   
   September 2011 and September 2014. Image Credit: NASA JPL   
       
   Earlier this year, at the peak of California's current three-year drought, the   
   team found that water storage in the state's Sacramento and San Joaquin river   
   basins was 11 trillion gallons below normal seasonal levels. Data collected   
   since the launch of GRACE in 2002 shows this deficit has increased steadily.   
       
   "Spaceborne and airborne measurements of Earth's changing shape, surface   
   height and gravity field now allow us to measure and analyze key features of   
   droughts better than ever before, including determining precisely when they   
   begin and end and what their magnitude is at any moment in time," Famiglietti   
   said. "That's an incredible advance and something that would be impossible   
   using only ground-based observations."   
       
   GRACE data reveal that, since 2011, the Sacramento and San Joaquin river   
   basins decreased in volume by four trillion gallons of water each year (15   
   cubic kilometers). That's more water than California's 38 million residents   
   use each year for domestic and municipal purposes. About two-thirds of the   
   loss is due to depletion of groundwater beneath California's Central Valley.   
       
   In related results, early 2014 data from NASA's Airborne Snow Observatory   
   indicate that snowpack in California's Sierra Nevada range was only half of   
   previous estimates.   
       
   The observatory is providing the first-ever high-resolution observations of   
   snow water volume in the Tuolumne River, Merced, Kings and Lakes basins of the   
   Sierra Nevada and Uncompahgre watershed in the Upper Colorado River Basin.   
       
   To develop these calculations, the observatory measures how much water is in   
   the snowpack and how much sunlight the snow absorbs, which influences how fast   
   the snow melts. These data enable accurate estimates of how much water will   
   flow out of a basin when the snow melts, which helps guide decision about   
   reservoir filling and water allocation.   
       
   "The 2014 snowpack was one of the three lowest on record and the worst since   
   1977, when California's population was half what it is now," said Airborne   
   Snow Observatory principal investigator Tom Painter of JPL. "Besides resulting   
   in less snow water, the dramatic reduction in snow extent contributes to   
   warming our climate by allowing the ground to absorb more sunlight. This   
   reduces soil moisture, which makes it harder to get water from the snow into   
   reservoirs once it does start snowing again."   
       
   New drought maps show groundwater levels across the U.S. Southwest are in the   
   lowest two to 10 percent since 1949. The maps, developed at NASA's Goddard   
   Space Flight Center in Greenbelt, Maryland, combine GRACE data with other   
   satellite observations.   
       
   "Integrating GRACE data with other satellite measurements provides a more   
   holistic view of the impact of drought on water availability, including on   
   groundwater resources, which are typically ignored in standard drought   
   indices," said Matt Rodell, chief of the Hydrological Sciences Laboratory at   
   Goddard.   
       
   The scientists cautioned that while the recent California storms have been   
   helpful in replenishing water resources, they aren't nearly enough to end the   
   multi-year drought.   
       
   "It takes years to get into a drought of this severity, and it will likely   
   take many more big storms, and years, to crawl out of it," said Famiglietti.   
       
       
   Credits and more information:   
   Production editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   NASA monitors Earth's vital signs from land, air and space with a fleet of   
   satellites and ambitious airborne and ground-based observation campaigns. The   
   agency develops new ways to observe and study Earth's interconnected natural   
   systems with long-term data records and computer analysis tools to better see   
   how our planet is changing. The agency shares this unique knowledge with the   
   global community and works with institutions in the United States and around   
   the world that contribute to understanding and protecting our home planet.   
       
   For more information on GRACE, visit http://www.nasa.gov/grace and   
   http://www.csr.utexas.edu/grace   
       
   For more on the Airborne Snow Observatory, visit: http://aso.jpl.nasa.gov/   
       
   For more information about NASA's Earth science activities, visit:   
   http://www.nasa.gov/earthrightnow   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.99   
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