We have developed wetness/drought indicator maps for shallow groundwater and surface and root zone soil moisture.  The maps integrate data from multiple ground and space based observing systems, including NASA's Gravity Recovery and Climate Experiment (GRACE) satellite mission.  The GRACE satellite pair detects small changes in the Earth's gravity field caused by the redistribution of water on and beneath the land surface.  The data are integrated within a sophisticated numerical model of land surface hydrological and energetic processes.  Using a long-term meteorological dataset, we have generated a continuous record of soil moisture and groundwater that stretches back to 1948.  The maps are meant to depict wetness conditions and drought associated with climatic variability, as opposed to depletion of aquifers due to groundwater withdrawals that exceed recharge.  They are updated weekly, incorporated into the U.S. Drought Monitor, and distributed through the National Drought Mitigation Center's data portal.

http://drought.unl.edu/MonitoringTools/NASAGRACEDataAssimilation.aspx