Animation showing Terrestrial Water Storage Anomaly (TWSA) data from March 2015 to March 2016. Shades of orange indicate areas with less ground water than normal and shades of blue are areas with more ground water than normal, which correlates to droughts and floods in these various regions.
A pair of experimental twin satellites called the Gravity Recovery And Climate Experiment, or "GRACE", were launched in March 2002. Since then they have been collecting gravity measurements which scientists use to derive Terrestrial Water Storage Anomalies (TWSA). TWSA can then be used as an indicator for drought and flood conditions across the globe. For more information on the GRACE mission please visit http://www.nasa.gov/mission_pages/Grace/
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 22.214.171.124.0